EEVblog #777 - Keithley 177 Microvolt DMM Repair

[EEVblog]

Come on a ride as Dave repairs an intermittent Keithley 177 Microvolt DMM, garden paths and all.
Service manual & Schematic: http://www.utwente.nl/tnw/slt/doc/apparatuur/multimeters/keithley177.pdf
Datasheet: http://www.datasheets.pl/integrated_circuits/I/ICL/ICL71C03.pdf
555 Timer T-Shirt:
http://teespring.com/555timer-grey3
Negative Feedback T-Shirt in the EU:
https://fabrily.com/negativefeedback

[German_EE]

1) If you look down the back of some of the switches there's a hole, squirt some switch cleaner down there with the meter front panel downwards.

2) Units like this have many switch contacts that are not used so wire a spare set in parallel to the burnt contacts.

Finally..........................

Keep your switch cleaner well away from the ADC circuits, if you contaminate the PCB it causes all sorts of strange readings (been there, done that)

[MBY]

Great video! I'm proud to be the one who fixed the schematics from my bad copy. Very glad to see that someone else had a use for it. It actually took many, many hours to draw those lines!

I had the exactly same problem, bad switches, and yes, the ohms and voltage switches were the worst. But, you actually can apply some contact spray on the ends (opposing ends from the front) and you also can take the switches apart without desoldering. They are a mess though. The pins, as you said, go across and the wipers contacts the pins directly. If you remove the front, then the metal bar in the front of the switches, the bar holding the wipers can be removed. The wipers are just loose metal tongues and will fall off when the wiper holding bar is removed. It's not trivial to put it all together again, but this is what I was forced to do to fix those intermittent problems.

After the fix, the instrument worked again for many years, until this very summer (northern hemisphere) , when the instrument suddenly fell out of calibration, showing about 20% to high values on all voltage ranges. This is outside the possible calibration ranges of the trimpots. I suspect it may be due to the summer here in Sweden, which has been unusual wet with RHs approaching 80%, so I will wait to the autumn and try to recalibrate it.

The unpopulated socket was correctly identified in the video as a plug-in socket for a serial- or HPIB-interface, not for an IC. I actually made my own interface for it to my own specification and has therefore invested a lot in the instrument, why I also will go the extra mile to recalibrate it once more (even if it takes replacement of components).

I believe I have discussed the RS232 interface in another thread (the thread where I posted the schematics).

Again, great video! Great recognition factor! Edit: And yes, all the same confusion. I also looked at the chopper circuits, discovered the two chip chipset, and also desoldered and checked all the pots. And, after the fix, made some modifications with my interface board. Negative input and system ground is the same potential, so it was possible to have a relay with a resistor to +5V and voliá - free diode measurement range! (Control from RS232, not from front panel.)

[TheRevva]

If you're quick, there's a 179 (TRMS) going REAL cheap on ebay right now...  US$15 is the current bid with < 2hrs remaining!
I was tempted to bid myself, but I want at least 5 1/2 digits (OK, I actually WANT 8 1/2 digits, but can only afford 5 1/2... LOL)

[EEVblog]

Great video! I'm proud to be the one who fixed the schematics from my bad copy. Very glad to see that someone else had a use for it. It actually took many, many hours to draw those lines!

Thanks for that, proved useful!

[Fungus]

Short a test point with a multimeter on the amps range? ...because it's fused?

Be sure to use a Fluke with those $12 fuses in it.

[tombi]

Probably too late now but when it randomly came good during testing, could it have been when you touched one of the terminals with your hand (and grounded the charge build up)?

[Fungus]

2) Units like this have many switch contacts that are not used so wire a spare set in parallel to the burnt contacts.

The manufacturers don't already do that to increase reliability? 

[EEVblog]

Probably too late now but when it randomly came good during testing, could it have been when you touched one of the terminals with your hand (and grounded the charge build up)?

Nope, it often just came good (or went bad) without getting close to it.

[Fungus]

What about the exploded resistor? Didn't that break anything?

[EEVblog]

Short a test point with a multimeter on the amps range? ...because it's fused?
Be sure to use a Fluke with those $12 fuses in it.

If shorting a test point blows a 10A fuse, then might just be thankful you used a fused meter and safe probes to do that instead of just using a bit of wire 

[EEVblog]

What about the exploded resistor? Didn't that break anything?

Yes, it seems it took out the diode bridge.

[Fungus]

What about the exploded resistor? Didn't that break anything?

Yes, it seems it took out the diode bridge.

But doesn't it need a new resistor?

[elex_enthusiast]

It's quite nice to have such a meter on my bench but unfortunately I'm too far away from AUS (I'm from Philippines) and a good friend of mine ( who happens to be an Australian and a member here) just sent a box yesterday containing an analog scope and some other stuff that he donated to me. Well I guess someone out there deserves that meter.

[retrolefty]

I suspect that good troubleshooting procedures and making a video simultaneously is an impossible task. As a 'professional troubleshooter' to component level for most of my working career (now retired), I was yelling at you almost non-stop watching this video.

 So many fail walks into the tall weeds, jumping to false conclusions, improper symptom recognition. However I couldn't stop watching the whole thing.     It was like reliving past battles.

 I think good troubleshooting skills is as much an art as learned skill. I feel you proceeded much too quickly and didn't think carefully enough about each analysis, decision, and path you made as you walked down the problem. That's probably because you also have to keep feeding audio talking points while trying to troubleshooting at the same time. Most brains are too small to pull that off successfully. 

 To be useful as a teaching moment, such a video troubleshooting task should be 'scripted' where you previously did the complete troubleshooting process and then create and follow a show and tell script to share your decision steps that lead to solving the problem.

 All that said, intermittent problems are the worst case symptoms to have to deal with. 

 

   

[AF6LJ]

I have always hated those slide switches, even though by design they are self cleaning.
My experience working on now older Motorola two way radio gear that used those switches. (Micor systems 90 Syntor and Syntor X radio gear.) Their self cleaning feature becomes less effective as the switches are used.
You actually can get contact cleaner/lube in to the sealed ones since the ends are open..
I have to confess I was the one who started screaming "clean the switches" at 10:00 into the video.
Sorry....

[eV1Te]

Nice job with the troubleshooting Dave and David, I was the one who sent you the DMM almost a year ago. I am also glad to hear that you decided to give it away to someone who needs it more!

I want to explain the lack of finesse on the diode bridge repair by saying that single diodes was the only thing available in the drawers in the lab at the time and the only available soldering iron was a large-tipped mains powered one! Maybe Dave has a rectifying bridge in a SIL package on hand which he can replace the diodes with at the same time as he replaces the blown resistor before giving it away? 

I can also clarify that 30 kV was never connected to the DMM, we only had a low power 30 kV arc/discharge through the air a few meters away from the DMM. But the electromagnetic radiation from this arc probably caused some component to latch-up which shorten the supply rail which in turn burned the diode bridge (my theory). I believe that the burned resistor close to the output has been like that for a much longer time and is not related to any faults you saw now.

I am equally surprised as you were regarding that the solution was only to clean the contacts. Because the meter worked fine just a day or two before the diode bridge broke and I would never have guessed that the contacts could become bad from that. After all maybe there was an ESD inside the DMMs contacts even though the DMM did not have any leads attached to it but was connected to mains at the time of the 30 kV arcing event which took place in the same room.

/Richard

[eV1Te]

double post....

[FireBird]

Could it be that the ADC checks should have been done with TP1 and TP2 still shorted?

[retrolefty]

Could it be that the ADC checks should have been done with TP1 and TP2 still shorted?

 Yes, but he did flash a message box stating that (after the fact) even before the long trip into the weeds.

[AF6LJ]

Nice job with the troubleshooting Dave and David, I was the one who sent you the DMM almost a year ago. I am also glad to hear that you decided to give it away to someone who needs it more!

I want to explain the lack of finesse on the diode bridge repair by saying that single diodes was the only thing available in the drawers in the lab at the time and the only available soldering iron was a large-tipped mains powered one! Maybe Dave has a rectifying bridge in a SIL package on hand which he can replace the diodes with at the same time as he replaces the blown resistor before giving it away? 

I can also clarify that 30 kV was never connected to the DMM, we only had a low power 30 kV arc/discharge through the air a few meters away from the DMM. But the electromagnetic radiation from this arc probably caused some component to latch-up which shorten the supply rail which in turn burned the diode bridge (my theory). I believe that the burned resistor close to the output has been like that for a much longer time and is not related to any faults you saw now.

I am equally surprised as you were regarding that the solution was only to clean the contacts. Because the meter worked fine just a day or two before the diode bridge broke and I would never have guessed that the contacts could become bad from that. After all maybe there was an ESD inside the DMMs contacts even though the DMM did not have any leads attached to it but was connected to mains at the time of the 30 kV arcing event which took place in the same room.

/Richard

There may have been some other reason the diodes blew, as for that resistor over in the right rear corner.... who knows... The switch issue is common among test equipment that is old enough to vote and certainly among gear that is old enough to have grandchildren, such as my Tek 466 storage scope. The primary culprit is oxidation, even in a Class 100 clean room (back when I spent some time working in one) oxidation was an issue.
I have a friend who owns several Keithley meters including a 177 from that time period and once and a while he just has to exercise the switches to clean the oxidation out. Those are good meters, going to have to add one to my bench

[FireBird]

but he did flash a message box stating that

Ok, that was a YouTube note and not in the downloaded video I've watched.

[Vgkid]

Good job Dave/David. I'm an avid hater of those ganged type switches.

[craigh]

Thanks for doing the video Dave.  I too was screaming at the monitor - clean the switches!

I purchased one of these 177s last year from eBay.  Seller claimed it worked OK, but when I got it, it was doing the same as yours.  The first thing I did was sprayed some contact cleaner into the switches and worked them.  Problem solved!  I now have a nice bench meter.

Early in my electronics career (early 1980s) I was troubleshooting and repairing many different types of equipment, similar vintage to the 177.  Often I solved some of the faults by cleaning all pots and switches with contact cleaner.  That's why I went first for the cleaner while fixing my 177.

Keep trying with the troubleshooting videos .

Craig.

[EEVblog]

but he did flash a message box stating that

Ok, that was a YouTube note and not in the downloaded video I've watched.

I cannot add text overlays to videos I have already uploaded to youtube, only youtube text annotations.
If you are watching a downloaded version of any video will miss those.
I often add annotations like that.

[EEVblog]

So many fail walks into the tall weeds, jumping to false conclusions, improper symptom recognition. However I couldn't stop watching the whole thing.     It was like reliving past battles.

To be fair, with my short playing with instrument before the video and also during the non-video breaks, there was no indication to me that the switches had a problem. It might look that way in the video perhaps, but it wasn't evident to me at the time, because yes, I am trying to shoot videos watching through the camcorder LCD screen.

I think good troubleshooting skills is as much an art as learned skill. I feel you proceeded much too quickly and didn't think carefully enough about each analysis, decision, and path you made as you walked down the problem.

Why?
I did a visual as you are supposed to.
Nothing mechanical was evident to me at the time (the switches only played ball later)
I had reason to suspect there was a component failure due to overload.
I had a simple and quick troubleshooting procedure so I started to follow it (that without the camera would have taken mere minutes)
A totally valid repair procedure.

Sure I could have sat there with the schematic for 30 minutes thinking why i would charge up and down etc and do the things it was, and I might have suspected the switched and then methodically started to play with then to reproduce the fault.
But meh, it went down how it went down. If I did this 10 times I would likely have gone down 10 different ways.

To be useful as a teaching moment, such a video troubleshooting task should be 'scripted' where you previously did the complete troubleshooting process and then create and follow a show and tell script to share your decision steps that lead to solving the problem.

I don't do scripts.
And I think it was a very useful video and did follow a reasonably correct procedure. I video were I just intuitively came to the conclusion that it was the switches from the get-go would have been the most boring video ever. I'm glad it didn't go down that way.
Sure in the end it turned out the problem could have been found earlier, but meh, the luck of the game.
I could have edited out all the dead ends, and made myself look like a repair genius, but that would not have made for an honest nor interesting video. I think there is great value in showing what happened warts and all.
If I had done what you suggested for this repair, it would be a 5 minute video with no electronics troubleshooting at all.
The warts and all real-time approach I take also gives views the time and ability to think about it and spot the fault themselves before I find it. There is huge value in that, and I think makes for a much more interesting video than a scripted route-step tutorial.

[Lightages]

I agree Dave. This video showed how to troubleshoot, and what can lead you down the garden path. No complaints from me! 

[SilverSolder]

A stab at a Golden List of Troubleshooting Intermittent Faults:

1. Thou shalt carefully inspect the boards and components looking for burned or damaged components, cracks in the PCB, bulging/leaking capacitors, etc., and repair as necessary.

2. Thou shalt measure / verify supply voltages and repair as necessary.

3. Thou shalt clean any switches, relays, pots, and connectors in the signal path with high quality cleaning fluids.  (This fixes 90% of older equipment problems in my experience)

4. Still problems? Thou shalt wriggle power resistors and any other PCB mounted component that gets hot, looking for open/bad, cracked, or intermittent solder joints (especially for lead free boards).

5. Still problems? Thou shalt use freeze spray, hot air gun etc. to thermally massage suspect components to see if that provokes a fault.

6. Still problems? - Now it's time to get creative and start a "divide and conquer" process of elimination, try to divide the circuit in half, inject signals if necessary, and verify each half at a time (binary search strategy).

[AF6LJ]

I agree Dave. This video showed how to troubleshoot, and what can lead you down the garden path. No complaints from me! 

While I agree mostly I think what was left out was the experience of a more adapt technician.
Note to Dave;
Don't get mad at me for saying this but it is true; Engineers make poor technicians, a tech is much better at troubleshooting. That is what we do from a repair standpoint we have component history and history that goes with various pieces of gear we have worked on. We know the points of failure and can set the analysis aside and get eh job done. The tests Dave-2 did should have been done in the first ten minutes, sorry but when you work as a tech for a living your job depends on finding the obvious. Dirty switches are obvious.
You do what you do wall as an engineer, there are damned few engineers who are also good techs, they are the one in twenty...

[AF6LJ]

A stab at a Golden List of Troubleshooting Intermittent Faults:

1. Thou shalt carefully inspect the boards and components looking for burned or damaged components, cracks in the PCB, bulging/leaking capacitors, etc., and repair as necessary.

2. Thou shalt measure / verify supply voltages and repair as necessary.

3. Thou shalt clean any switches, relays, pots, and connectors in the signal path with high quality cleaning fluids.  (This fixes 90% of older equipment problems in my experience)

4. Still problems? Thou shalt wriggle power resistors and any other PCB mounted component that gets hot, looking for open/bad, cracked, or intermittent solder joints (especially for lead free boards).

5. Still problems? Thou shalt use freeze spray, hot air gun etc. to thermally massage suspect components to see if that provokes a fault.

6. Still problems? - Now it's time to get creative and start a "divide and conquer" process of elimination, try to divide the circuit in half, inject signals if necessary, and verify each half at a time (binary search strategy).

That is actually good advice and will get the problem solved 95% of the time.

[dentaku]

I suspect that good troubleshooting procedures and making a video simultaneously is an impossible task. As a 'professional troubleshooter' to component level for most of my working career (now retired), I was yelling at you almost non-stop watching this video.

 So many fail walks into the tall weeds, jumping to false conclusions, improper symptom recognition. However I couldn't stop watching the whole thing.     It was like reliving past battles.

 I think good troubleshooting skills is as much an art as learned skill. I feel you proceeded much too quickly and didn't think carefully enough about each analysis, decision, and path you made as you walked down the problem. That's probably because you also have to keep feeding audio talking points while trying to troubleshooting at the same time. Most brains are too small to pull that off successfully. 

 To be useful as a teaching moment, such a video troubleshooting task should be 'scripted' where you previously did the complete troubleshooting process and then create and follow a show and tell script to share your decision steps that lead to solving the problem.

 All that said, intermittent problems are the worst case symptoms to have to deal with. 

 

Shahriar has had a good stretch of interesting repair videos lately. He lives a place where it's easier to find good equipment to fix than Australia too.
https://www.youtube.com/channel/UCKxRARSpahF1Mt-2vbPug-g

[AF6LJ]

Note to Dave;
Don't get mad at me for saying this but it is true; Engineers make poor technicians, a tech is much better at troubleshooting.

Could it be said that engineers know how things work and technicians know how things fail?

I was thinking clean the switches. But rather than feeling righteous I admit it was because I don't know enough about ADC integrators to be misled.

I do like to see old test equipment rescued. I hope Dave makes more repair videos.

Something like that, some technicians know how things work, some engineers know how things fail.
Just like some engineers do make good technicians and some technicians know engineering.
When I use to work for Loral Data Systems we had a few engineers who were really great technicians. One of them designed the first PLL synthesized L band transmitter (200 channels 1.43GHZ to 1.54GHZ). Electronics was his hobby and I might add his first name was Dave.

So it depends; every once and a while you come across a truly great engineer, very seldom do you find a really great engineer who is also a really good technician. They are out there....

[poot36]

How about fixing the Tektronix scopes that you got in a previous mailbag?

[EEVblog]

While I agree mostly I think what was left out was the experience of a more adapt technician.

Sure, and those who repair vintage gear like this all time would instantly know with maybe 90% certainly the switches would come first.
As retrolefty said, try doing this as a video blog and shooting and talking at the same time trying to get useful content in the bag, it's a completely different game.
The only thing I did "wrong" here is not detect the bad switches earlier.
Should I have suspected the bad switches from the get-go? In a bit of kit this vintage, perhaps, and I did think of it as I was playing. But as the person who sent it in said, it worked fine just days before the event that killed it. And when I first played with it there seemed to be no correlation between the switches and what was happening. But I eventually came to that conclusion.

Don't get mad at me for saying this but it is true; Engineers make poor technicians, a tech is much better at troubleshooting.

I started out as a repair tech, thank you very much 

That is what we do from a repair standpoint we have component history and history that goes with various pieces of gear we have worked on. We know the points of failure and can set the analysis aside and get eh job done. The tests Dave-2 did should have been done in the first ten minutes, sorry but when you work as a tech for a living your job depends on finding the obvious. Dirty switches are obvious.

I did do those tests! as part of an initial touchy feely before the video, and there was nothing obvious. And several things lead me away from suspecting the switches as well. I can hear people saying "yeah, yeah, excuses excuses" but hey, that's the way it went down. Meh.
I would have been mightily embarrassed if I had never suspected the switches and David2 came along and found it in 15 minutes. But I had already suspected the switches twice by that point, and was literally the next thing I was going to attack in-depth, it's all it could be by that point.
Also, as I've said, the tests I did, whilst 30 minutes of video and commentary, probably amount to 5 minutes actual work before I came to the conclusion that the switches were at fault. So this thing, in the real world would have been fixed in maybe 10 minutes.

[EEVblog]

So it depends; every once and a while you come across a truly great engineer, very seldom do you find a really great engineer who is also a really good technician. They are out there....

It depends on what you do every day.
A good TV repair tech will fix a TV faster than anyone, engineer or tech.
A good system production tech will likely fix system production issues 10 times faster than that top TV repair tech.
A good RF design engineer who troubleshoots RF prototype circuits all day long will likely repair an RF amp quicker than any tech ever could.
It's horses for courses.

I used to be a repair tech on Z80 based CCTV gear, and I was the best one they ever had. At point I would have wagered I could repair that gear quicker and more efficiently than anyone else on the planet.
Would I be able to do that now 25 years later? Not a chance, I'd bumble around like anyone else would.

[EEVblog]

Shahriar has had a good stretch of interesting repair videos lately. He lives a place where it's easier to find good equipment to fix than Australia too.

Yes, gear is not easy or cheap to get in Oz. Majority of US sellers won't even ship outside the US or Canada.
BTW, I just scored a Fluke bench meter. Sold as not working, but I suspect it will be fully working...

[tech5940]

So happy to see a new repair video, thanks Dave!


Sent from my iPad using Tapatalk

[EEVblog]

How about fixing the Tektronix scopes that you got in a previous mailbag?

Those scopes are notoriously horrible to fix. Uses a ton of custom parts. My spidy sense tells me it would just end up like the DSA repair.

[beaker353]

Over the past decade as a industrial equipment bench tech I would say about 95% of my repairs come down to either the power supply or something electro-mechanical. I always throughly check both before pushing into component level tests.

-EM


Sent from my iPhone using Tapatalk

[dentaku]

Shahriar has had a good stretch of interesting repair videos lately. He lives a place where it's easier to find good equipment to fix than Australia too.

Yes, gear is not easy or cheap to get in Oz. Majority of US sellers won't even ship outside the US or Canada.
BTW, I just scored a Fluke bench meter. Sold as not working, but I suspect it will be fully working...

Shahriar also has the advantage of working at Bell Labs so his dumpster has way higher end stuff in it too, but good Ebay finds are definitely much easier to get in New Jersey.

[EEVblog]

Over the past decade as a industrial equipment bench tech I would say about 95% of my repairs come down to either the power supply or something electro-mechanical. I always throughly check both before pushing into component level tests.

In my repair days, almost all the repairs were component level failures.

[AF6LJ]

So it depends; every once and a while you come across a truly great engineer, very seldom do you find a really great engineer who is also a really good technician. They are out there....

It depends on what you do every day.
A good TV repair tech will fix a TV faster than anyone, engineer or tech.
A good system production tech will likely fix system production issues 10 times faster than that top TV repair tech.
A good RF design engineer who troubleshoots RF prototype circuits all day long will likely repair an RF amp quicker than any tech ever could.
It's horses for courses.

I used to be a repair tech on Z80 based CCTV gear, and I was the best one they ever had. At point I would have wagered I could repair that gear quicker and more efficiently than anyone else on the planet.
Would I be able to do that now 25 years later? Not a chance, I'd bumble around like anyone else would.

I'll bet you could once you been on the bicycle you never forget how to ride it.
I bought an S-Band transmitter off E-Bay a couple of years back, happened to be one I and an assembler built when I worked at Loral Corp. I wanted a piece of my past and a paperweight. As soon as I opened it up that experience all came flooding back. I have no doubt I could build / align those transmitters twenty nine years later.
I think you might be surprised as to how much you retain, it just takes a little stimulus to get it back out and into your hands.

[AF6LJ]

Shahriar has had a good stretch of interesting repair videos lately. He lives a place where it's easier to find good equipment to fix than Australia too.

Yes, gear is not easy or cheap to get in Oz. Majority of US sellers won't even ship outside the US or Canada.
BTW, I just scored a Fluke bench meter. Sold as not working, but I suspect it will be fully working...

Good deal, on the Fluke.
The US market for used (affordable) gear is starting to dry up

[EEVblog]

I'll bet you could once you been on the bicycle you never forget how to ride it.

Yeah, but I don't think I'd be as good as I was back then. I know a lot more now, and sometimes that can be a hindrance
i.e. a lot more complex stuff stuff that could cause various faults jumps into my head instantly more now than it did back then. There is definitely something in the "engineers can overthink things" line.

There is also a fair bit of psychology involved too. In the case the of the Keithley here, and most of my video repairs, I go into it secretly hoping it's going to be some elusive electronics fault that I can track down like an episode of Columbo. And that probably subconsciously influences how I do things.

[c4757p]

Over the past decade as a industrial equipment bench tech I would say about 95% of my repairs come down to either the power supply or something electro-mechanical. I always throughly check both before pushing into component level tests.

In my repair days, almost all the repairs were component level failures.

Interesting, what sort of things were you repairing? Electromechanical problems are by far the ones I see the most as well.

[krivx]

Over the past decade as a industrial equipment bench tech I would say about 95% of my repairs come down to either the power supply or something electro-mechanical. I always throughly check both before pushing into component level tests.

In my repair days, almost all the repairs were component level failures.

Interesting, what sort of things were you repairing? Electromechanical problems are by far the ones I see the most as well.

I feel like the amount of human handling is going to influence things - think of broken switches in things that get touched often versus dried capacitors in things that don't. I would guess that CCTV systems are mostly set-and-forget, so mechanical failure doesn't happen (assuming stationary cameras...)

[SeanB]

Bad connections are common, along with failed power supplies. Funny enough the most reliable connectors are the F connectors, they only give grief after a few years. A shot od spray lube on the end and reconnect and it works again for a decade. Worst is those phono/RCA connectors, they do horrid things.

Then you get the painters who paint everything, including the camera lenses.......

[retrolefty]

I'll bet you could once you been on the bicycle you never forget how to ride it.

Yeah, but I don't think I'd be as good as I was back then. I know a lot more now, and sometimes that can be a hindrance
i.e. a lot more complex stuff stuff that could cause various faults jumps into my head instantly more now than it did back then. There is definitely something in the "engineers can overthink things" line.

There is also a fair bit of psychology involved too. In the case the of the Keithley here, and most of my video repairs, I go into it secretly hoping it's going to be some elusive electronics fault that I can track down like an episode of Columbo. And that probably subconsciously influences how I do things.

 But grasshopper, Colombo episodes were all scripted, and you don't do scripted. 

[AF6LJ]

I'll bet you could once you been on the bicycle you never forget how to ride it.

Yeah, but I don't think I'd be as good as I was back then. I know a lot more now, and sometimes that can be a hindrance
i.e. a lot more complex stuff stuff that could cause various faults jumps into my head instantly more now than it did back then. There is definitely something in the "engineers can overthink things" line.

Technicians fall into that trap also, it has happened to me a few times and I have seen it often happen to others, especially being an RF tech for nearly all my career.

There is also a fair bit of psychology involved too. In the case the of the Keithley here, and most of my video repairs, I go into it secretly hoping it's going to be some elusive electronics fault that I can track down like an episode of Columbo. And that probably subconsciously influences how I do things.

Here is a good one for you that had three senior techs baffled (yes I was one of the three).
When I worked at Loral Corp I was building 1.5 GHZ FM exciters, they would drive a ten watt three transistor PA(aligning testing and some assembly but the majority was left to the assemblers...)
We had the second transmitter of 175 kicked back for failing vibration testing. The transmitter signal would start breaking up on the spectrum analyzer and it would do it at a nice linear rate. as you brought up the random vibe level the carrier would become more broken up in proportion to the amount of Gs the transmitter was subject to.

So the transmitter gets kicked back to QA, the top assembly tech ruled out the PA and the voltage regulator and kicked the exciter back to me. I ran the exciter did some "thumping on the Loop can, Miser board, VCO and Crystal oscillator modules. The loop was broken and I came to the conclusion that the VCO (for whatever reason) was sensitive to mechanical shock. The VCO is potted by the way. So back to the tech who aligned it, it goes..
Four days later he sends it back with a half dozen pages of work done and it is suppose to be good... I preform the same test and say it is still bad... Well I can't just send it back and I am busy turning out those other 174 exciters so reworking the VCO myself is out of the question...The third trip around my Boss's boss gets involved.
He says "Well Sue maybe it is the loop" I say "No sir I married the VCO with another exciter and the VCO is bad...
So now this exciter becomes a political football...
We set it aside and as we approach the end of the contract the exciter takes a trip to engineering. One morning an Engineer (who just happened to be named Dave (not the first Dave but another one) comes back with my exciter minus the VCO. He says this is good we are holding the VCO...
By this time that VCO had all the active and passive parts in the VCO cavity replaced still didn't work. There was an isolator a 100pf feedthrough cap, a 100pf feedthrough and a CK05 type ceramic cap soldered to the outside. of the VCO cavity. This almost stumped the Engineering department until the last remaining parts were tested with a newly purchased vibration probe. Turns out that CK05 ceramic cap had become piezoelectric, and was modulating the VCO supply voltage.

That is the kind of problem I know you would love to solve.

[poot36]

Those scopes are notoriously horrible to fix. Uses a ton of custom parts. My spidy sense tells me it would just end up like the DSA repair.

But even if it does it would be a great teaching tool and if it doesn't then you get a working high end (for the time) scope.

[boffin]

There is also a fair bit of psychology involved too. In the case the of the Keithley here, and most of my video repairs, I go into it secretly hoping it's going to be some elusive electronics fault that I can track down like an episode of Columbo. And that probably subconsciously influences how I do things.

Just one more thing 

While the rails gave +/- 15, how stable was it?  I would have been inclined to pop a scope on the power supplies to see if they had 2-3v of ripple.  If the bridge got ker-powed, I would look next door at the supply caps.

[John Coloccia]

Spraying cleaner on switches 2 minutes into the video would have been a pretty boring video. I kind of enjoyed seeing the troubleshooting if for nothing else than it's interesting to see the thought that went into writing the manual.  Trouble shooting manuals today are written for idiots servicing disposable items:

Problem: No Sound
1) check if the device is plugged in
2) check that the speakers are plugged in

If you still have no sound, throw it out.

Problem: No video
1) check that the device is plugged in
2) check that the monitor is plugged in

If you still have no video, throw it out.

It's nice to see some old school, nuts and bolts, grown up engineering!

[DanielS]

As an owner of a ~30 years old amplifier (the first stereo my parents bought when I was a kid that my mother gave to my grandmother and then inherited back after my grandmother passed), I am quite well acquainted with the effects of crusty old switches since I periodically have to cycle though most of the amplifier's switches when it starts popping or dropping out. As soon as I noticed that values tended to "come good" after switching ranges when Dave started playing with it, I suspected the switches.

I really should remember to try contact cleaner next time I open it for a tune-up, that could spare me a few minutes of frustration every couple of days. Now that I have a scope, I really should poke around and see if I can fix the gain mismatch between channels too.

[EEVblog]

As soon as I noticed that values tended to "come good" after switching ranges when Dave started playing with it, I suspected the switches.

It just as often didn't come good or go bad when the switches were changed. And often it would just come good all on it's own without touching anything. It seemed possessed!

[vlad777]

You can spray all the switches from the back side (plunger is visible).
Is it just me, or the two switches in question have wires on them that also should be sprayed.

Edit:
That plug is not "funny". It is a European 220V plug.

[EEVblog]

That plug is not "funny". It is a European 220V plug.

Yeah, like I said, funny.

[vlad777]

What IS funny is that unit has 220V plug and set for 110V ?

[phamuc]

Hey Dave,

You may want to check to bottom side of the PCB.
The gang of switches may have hairline solder cracks around some of the pins. Especially after years of use, and two Australians banging on the thing 
Maybe reheat the connections to be safe.


 I also didn't see you check the bottom of the PCB for blown lands, the thing did get a 30KV pulse that blew a resistor.

-Paul

[AF6LJ]

As an owner of a ~30 years old amplifier (the first stereo my parents bought when I was a kid that my mother gave to my grandmother and then inherited back after my grandmother passed), I am quite well acquainted with the effects of crusty old switches since I periodically have to cycle though most of the amplifier's switches when it starts popping or dropping out. As soon as I noticed that values tended to "come good" after switching ranges when Dave started playing with it, I suspected the switches.

I really should remember to try contact cleaner next time I open it for a tune-up, that could spare me a few minutes of frustration every couple of days. Now that I have a scope, I really should poke around and see if I can fix the gain mismatch between channels too.

The old gear is fun, I have plenty of it myself.
Just a word of caution regarding contact cleaner and switches. (post are a different story)
The insulating material on some switches will soak up the contact cleaner, that material will swell up and cause the rivits holding the contacts to become loose. This will make for a bigger, and more persistent problem. As a general rule switch contacts are self cleaning, especially rotary switches. A little (very little) lube on the shaft and detent will go a long way to keep those switches in working order.

[AF6LJ]

What IS funny is that unit has 220V plug and set for 110V ?

I think that would qualify as Scary.....
not funny.

[eV1Te]

What IS funny is that unit has 220V plug and set for 110V ?

I didn't think of that during the video, but I can assure you that the DMM was set for 230 V before I sent it. It must have flipped during shipping or when unpacking... A reminder that one should always check such switches before plugging in a device 

[MBY]

Hey Dave,

You may want to check to bottom side of the PCB.
The gang of switches may have hairline solder cracks around some of the pins. Especially after years of use, and two Australians banging on the thing 
Maybe reheat the connections to be safe.


 I also didn't see you check the bottom of the PCB for blown lands, the thing did get a 30KV pulse that blew a resistor.

-Paul

Yes, it surprised me too that Dave didn't check the bottom side of the PCB. The PCB is two sided and some soldering joints on my unit around the switches indeed needed a reflow.

And I can attest that I did go through the same path as Dave despite of suspecting the switches in the first place. No amount of cleaning, rubbing and switching did help at first and the problem were popping in and out of existence even if I wasn't anywhere near the unit. So I checked the rails, reference, chopper, divider and pots until I completely disassembled the switches for thorough cleaning.

And the switches are still somewhat unreliable. The wipers are okay, I'm sure. The problem is the pins that defies visual inspection (but allows scrubbing, spraying and so on).

As I mentioned in my earlier post, my unit quite recently fell out of calibration after many years of reliable operation. This time I suspect high humidity and I will wait for cooler and dryer weather before I do a recal. It is currently not possible to calibrate as the trimmers doesn't allow the range. Worst case scenario is to replace with new pots. And yes, it's time for another round of contact spray I would think...

[EEVblog]

You may want to check to bottom side of the PCB.

I did that. Wasn't in the video.

[DanielS]

The old gear is fun, I have plenty of it myself.
Just a word of caution regarding contact cleaner and switches. (post are a different story)
The insulating material on some switches will soak up the contact cleaner, that material will swell up and cause the rivits holding the contacts to become loose.

Yeah, there is that possibility too, depending on what sort of material is used for the insulation and the specific nature of the contact cleaner, much like how spraying fine petroleum-based lubricants on rubber is usually a bad idea since the lubricant will often either dissolve the rubber or cause it to dry out.

One of the switches is a fancy four positions linear  selector driven by a flat open-frame mechanical transmission cable which connects to a rotary knob on the front. Instead of bringing weak input signals to the front, they bring the mechanical input all the way to the rear to keep the signal path as short as possible.

[Old Fart Analog Engineer]

Doctors don't do well diagnosing themselves, Lawyers don't do well representing themselves, Architects do poorly at construction and Engineers do not troubleshoot well.  I too, was talking to the screen while going down this bizarre expedition.  When we started measuring film capacitors rated >100 V I started smiling (a wry, condescending smile, I'm afraid). Toward the end of nearly an hour, I was expecting an analysis of the fiber "orientation" of the fiberglass PCB. 

If engineers actually spent several years fixing the the things they design, they might find the weak points affecting durability and long life.  It took over 40 years for people to figure out that if they did not use thick gold for low current switches & contacts, they must use sealed relays or electronic cross-points. 

The problems encountered with old test equipment (& other commercial / medical electronics): 1) CONTACTS (connectors, switches, relays, potentiometers)  2) SOLDER CONNECTIONS  3) LOOSE GROUNDS, i.e  "grounding screws" from terminals or PCB to ground   4) Electrolytic Capacitors: the higher the voltage and larger the capacitance, the more suspect.   This is based on 100s of thousands of repairs.  No troubleshooting manual or schematic is needed for checking these.  Years of experience is.  Common sense of what is the most likely cause also helps.

The switches and relays used in this type of equipment can be several different types, but all have some factors common.  Low current contacts (aka "signal" / "dry" / "logic level") have either brass, alloy, silver or gold plating on the contact points.  Most are silver.  If the visible parts of the contact are gray or black, the silver is oxidized. Silver Oxide is an insulator.  Certain contact cleaners will clean these well.  The "grease" you may find is not there primarily as a mechanical lubricant, but to keep oxygen away from the silver.  After cleaning with a spray liquid cleaner, the "grease" is washed away, ensuring future contact problems.  To make a lasting repair, use an electric grade of silicone grease on both the moving and stationary contacts.  If there are still issues, disassemble the contacts, clean them (IPA works) and look at them under well lit magnification.  If it has the silver or gold worn away by mechanical friction from use, your only option is to replace the switch or relay (or even pot).  This is usually impossible.  Another alternative is to add and wire-in relays or semiconductor switches. 

This is the major issue with used test equipment from eBay.  Even if it works flawlessly, or is "not right", "out of calibration", or the dreaded "intermittent", clean all contacts (switches, relays, connectors, pots) first! CAIG makes some great products for this http://store.caig.com/s.nl/sc.2/category.292/.f   http://store.caig.com/s.nl/sc.2/category.188/.f.  Don't use any cleaner which is flammable, because these may harm / swell the plastics holding the contacts.  When buying test equipment without being able to have it inspected by someone who knows what to look for prior to purchase, assume that it will need 'fixin' and that parts may not be available and that whatever you pay for the item and shipping will be lost.

OFAE

[AF6LJ]

The old gear is fun, I have plenty of it myself.
Just a word of caution regarding contact cleaner and switches. (post are a different story)
The insulating material on some switches will soak up the contact cleaner, that material will swell up and cause the rivits holding the contacts to become loose.

Yeah, there is that possibility too, depending on what sort of material is used for the insulation and the specific nature of the contact cleaner, much like how spraying fine petroleum-based lubricants on rubber is usually a bad idea since the lubricant will often either dissolve the rubber or cause it to dry out.

One of the switches is a fancy four positions linear  selector driven by a flat open-frame mechanical transmission cable which connects to a rotary knob on the front. Instead of bringing weak input signals to the front, they bring the mechanical input all the way to the rear to keep the signal path as short as possible.

That is some fine design, and you use to see that or variations of that used in quality stereo / Hifi equipment of a time gone by. Then there is this....
A marginal mechanical design in a piece of amateur radio gear built to a cost.

Underside view of the Galaxy V transceiver. Sorry for the crappy picture.
It is the only one I had and I couldn't find any of the underside on the net.

I might add this must have been made back in the days when Men were Men, because it takes about 5 foot pounds of to9rque to turn the band switch even it is clean, lubed and all the switches and couplings are aligned to limit binding. otherwise the radio is a real POS....

[Tothwolf]

How about fixing the Tektronix scopes that you got in a previous mailbag?

Those scopes are notoriously horrible to fix. Uses a ton of custom parts. My spidy sense tells me it would just end up like the DSA repair.

Nope, sorry Dave. Those Tektronix 24x5 scopes would be far easier to repair than the DSA. I'm active in the tekscopes community and I own one of these scopes. The two most common problem areas are the aluminum electrolytics in the PSU failing due to age and the SMD aluminum electrolytics on some of the later processor boards can leak and do minor board damage. Another somewhat common problem area are the versions of these scopes with use a Dallas battery backed memory module. When those fail, the scope looses its cal data. All of these issues can be overcome without that great of difficulty. While these scopes can have failed hybrid modules, those faults are not very common, and those parts can also be found with some asking around. Restoring one of these scopes is very labor intensive, but well worth it. The only real challenge I saw with your scopes is the missing covers, rear panels, and hardware. All of those parts are out there (I had to replace a number of broken/missing structural/mechanical parts on mine), but I suspect replacing all those missing parts on your scopes would cost somewhere in the neighborhood of $100 USD per scope.

As for the switches in the Keithley 177, those are a problem area in any gear of this vintage. 1980s Fluke and Simpson meters which use these type of push button (slide contact) switches tend to have the same sort of issues. Schadow (ITT) sold millions of these style of switches and they were used everywhere. Even my early 1980s vintage Tektronix 2213 scopes used a single push on/push off Schadow switch for the power button, which after 30+ years, tend to stick, and had to be serviced. What complicated matters with the 2213s, is they trimmed away the top connection pins on the switch and insulated it with a slide-on plastic cover. The cover cannot be removed to allow the switch to be cleaned without first desoldering it from the board, which involves a lot of disassembly.

[dr.diesel]

Speaking of, I need to renew my stock of contact cleaner/lube.  Is there a US version of that EML - Contact Cleaner Lubricant under a different name?  Doesn't appear to be readily available here in the US.

[EEVblog]

Restoring one of these scopes is very labor intensive, but well worth it.

That's why I'm not doing it, I don't have the time. Murphy will ensue that they will have all sorts of issues making any repair repair attempt even longer. It will turn into the DSA repair all over again, I know it.

The only real challenge I saw with your scopes is the missing covers, rear panels, and hardware. All of those parts are out there (I had to replace a number of broken/missing structural/mechanical parts on mine), but I suspect replacing all those missing parts on your scopes would cost somewhere in the neighborhood of $100 USD per scope.

You also have to try and get them in Oz.

[AF6LJ]

How about fixing the Tektronix scopes that you got in a previous mailbag?

Those scopes are notoriously horrible to fix. Uses a ton of custom parts. My spidy sense tells me it would just end up like the DSA repair.

Nope, sorry Dave. Those Tektronix 24x5 scopes would be far easier to repair than the DSA. I'm active in the tekscopes community and I own one of these scopes. The two most common problem areas are the aluminum electrolytics in the PSU failing due to age and the SMD aluminum electrolytics on some of the later processor boards can leak and do minor board damage. Another somewhat common problem area are the versions of these scopes with use a Dallas battery backed memory module. When those fail, the scope looses its cal data. All of these issues can be overcome without that great of difficulty. While these scopes can have failed hybrid modules, those faults are not very common, and those parts can also be found with some asking around. Restoring one of these scopes is very labor intensive, but well worth it. The only real challenge I saw with your scopes is the missing covers, rear panels, and hardware. All of those parts are out there (I had to replace a number of broken/missing structural/mechanical parts on mine), but I suspect replacing all those missing parts on your scopes would cost somewhere in the neighborhood of $100 USD per scope.

I would agree, we might have to talk about my two Tek 475s I plan on making one work... I know about the power supply issues they are legendary in Tek Scopes going way back.

As for the switches in the Keithley 177, those are a problem area in any gear of this vintage. 1980s Fluke and Simpson meters which use these type of push button (slide contact) switches tend to have the same sort of issues. Schadow (ITT) sold millions of these style of switches and they were used everywhere. Even my early 1980s vintage Tektronix 2213 scopes used a single push on/push off Schadow switch for the power button, which after 30+ years, tend to stick, and had to be serviced. What complicated matters with the 2213s, is they trimmed away the top connection pins on the switch and insulated it with a slide-on plastic cover. The cover cannot be removed to allow the switch to be cleaned without first desoldering it from the board, which involves a lot of disassembly.

That switch design is old as dirt. I have seem them in comm gear going back to the late 1960s.
They are reliable to a point, once the plating wears off they are Gonski...

[John Coloccia]

Speaking of, I need to renew my stock of contact cleaner/lube.  Is there a US version of that EML - Contact Cleaner Lubricant under a different name?  Doesn't appear to be readily available here in the US.

It's not the same stuff, but I've has excellent luck with Deoxit. I mainly use it because it doesn't generally damage guitar finishes, but it seems to work pretty well regardless.

[Tothwolf]

Restoring one of these scopes is very labor intensive, but well worth it.

That's why I'm not doing it, I don't have the time. Murphy will ensue that they will have all sorts of issues making any repair repair attempt even longer. It will turn into the DSA repair all over again, I know it.

The only real challenge I saw with your scopes is the missing covers, rear panels, and hardware. All of those parts are out there (I had to replace a number of broken/missing structural/mechanical parts on mine), but I suspect replacing all those missing parts on your scopes would cost somewhere in the neighborhood of $100 USD per scope.

You also have to try and get them in Oz.

I had to import the mechanical parts for my 24x5 from Greece and Israel... 

[Tothwolf]

The switches and relays used in this type of equipment can be several different types, but all have some factors common.  Low current contacts (aka "signal" / "dry" / "logic level") have either brass, alloy, silver or gold plating on the contact points.  Most are silver.  If the visible parts of the contact are gray or black, the silver is oxidized. Silver Oxide is an insulator.  Certain contact cleaners will clean these well.  The "grease" you may find is not there primarily as a mechanical lubricant, but to keep oxygen away from the silver.  After cleaning with a spray liquid cleaner, the "grease" is washed away, ensuring future contact problems.  To make a lasting repair, use an electric grade of silicone grease on both the moving and stationary contacts.  If there are still issues, disassemble the contacts, clean them (IPA works) and look at them under well lit magnification.  If it has the silver or gold worn away by mechanical friction from use, your only option is to replace the switch or relay (or even pot).  This is usually impossible.  Another alternative is to add and wire-in relays or semiconductor switches. 

Don't use any cleaner which is flammable, because these may harm / swell the plastics holding the contacts.

While I agree with a large portion of what you said, there are some things which need to be pointed out.

First, silver oxide is not an insulator. Silver oxide is very conductive and tarnished silver contacts by themselves are usually not a problem. If the tarnish is very "grainy" and the contacts are used in a low voltage circuit without debounce circuitry, usually only then is silver oxide a problem. The best way to clean these sort of contacts is a strip of thin cardboard or thick paper, pulled lightly through a closed set of contacts.

Second, silicone grease should never be used anywhere near electrical switch and relay contacts. Western Electric / Bell System and others all learned this the hard way back in the day with their electromechanical telephone exchange switches. When used in or near switch contacts which interrupt current, any arcing can cause the silicone to break down into silicon-carbide, which is not only electrically insulative, but also extremely hard and abrasive, which is very damaging to contacts. I personally use Sanchem "NO-OX-ID A-Special" grease when I need a grease for switch contacts. [Note however, this is NOT to be confused with "Ideal NOALOX" aluminum wire compound, which is a flammable abrasive paste which is supposed to penetrate aluminum oxide (it actually doesn't work very well since aluminum oxide is harder than the zinc particles that compound contains).]

As for flammable vs plastic-safe contact cleaners, many popular contact cleaners are flammable, and many non-flammable cleaners are not plastic safe.

Isopropyl Alcohol (isopropanol, IPA) for example, is extremely flammable, but plastic safe, and is one of the most common first-choice cleaners people use (not "rubbing alcohol", as this contains oils and a large percentage of water).

Cleaning solvents which should be avoided for electronics work contain such things as Acetone (Benzene), Trichloroethane, Tetrachloroethylene (Perchloroethylene), and similar. Acetone is flammable, Trichloroethane is low-flammability, and Tetrachloroethylene is non-flammable. All will readily dissolve plastics. Chlorinated cleaning solvents will also react with aluminum, and will also leach into and damage aluminum electrolytic capacitors (most capacitor manufacturers today explicitly warn about this in their datasheets).

I've been using CRC QD Contact Cleaner (02130) and CRC QD Electronic Cleaner (05103) to clean electrical contacts, potentiometers, and as a board wash for really stubborn stuff which doesn't completely clean off with Isopropyl Alcohol. Both are plastic-safe and contain Isohexane, Difluoroethane, and n-Hexane. The only difference I can tell between the current formulations of the two is QD Contact Cleaner contains Isopropyl Alcohol while QD Electronic Cleaner contains Ethanol. (Older formulations of QD Electronic Cleaner contained Naphtha and Methanol instead of the Ethanol.)

For switches and potentiometers, I usually follow these up with CRC 2-26 Plastic Safe Multi-Purpose Precision Lubricant (02004) which is basically Mineral Oil and some thickeners. This is pretty much the same stuff which used to be in TV tuner cleaners and contact cleaners which contained a lubricant. An added benefit to a separate lubricant is that it doesn't end up all over a pc board and everywhere else you really don't want it.

[Tothwolf]

Restoring one of these scopes is very labor intensive, but well worth it.

That's why I'm not doing it, I don't have the time. Murphy will ensue that they will have all sorts of issues making any repair repair attempt even longer. It will turn into the DSA repair all over again, I know it.

Well, Murphy or not, if you do eventually tackle these scopes PSU and processor boards, and you do some really careful, methodical step-by-step how-to videos covering the restoration process, I guarantee you that those repair videos will be some of your most popular. There are a ton of 24x5 scopes out there and people are constantly looking for repair information about the really common faults.

If you do decide to tackle them, there is one gotcha to be on the lookout for. The service manual has some component values wrong for some of the aluminum electrolytic capacitors on the PSU board. Many people discovered this the had way with their replacement electrolytics exploding. The Rifa brand class-X and class-Y safety capacitors (translucent yellow plastic) are also a must-replace item. All of this stuff has been well documented in the tekscopes email list archives though.

[marcan]

I think Dave's biggest troubleshooting fail here was not following a divide and conquer approach. If only he'd thrown a multimeter on the ADC input terminal, he could've ruled it out from the very beginning. After the obligatory troubleshooting steps (#0: look for blown stuff, #1: check the rails, #2: wiggle stuff), the right approach is to binary search the signal path until you narrow down the culprit, instead of guessing what the faulty component might be and dive right into troubleshooting it (making mistakes and creating red herrings for yourself along the way) before confirming that it really is borked to begin with.

Personally, though, as soon as I saw the creeping display and the correlation with changing ranges, I was thinking "faulty switches". But that's because I've seen a multimeter with a dodgy range switch do the same exact thing to me, so I'm lucky there (it was a cheapie chinese one, but the same principle applies). Experienced troubleshooters (especially of test equipment) will have the right hunches to save time, and you can't blame Dave for not having that. But knowing how to divide and conquer doesn't require experience, it's the basics, and I really feel that's where he messed up the procedure.

On an unrelated note, I don't think the blown resistor has anything to do with the fault, or anything to do with the blown diode bridge. Even if you short out the output, there's nothing driving it that could cause that resistor to blow. That resistor goes off to ground. We all know how you blow devices through the ground pin: by forgetting about earth reference. That thing was hooked up to a scope or something that is mains earth referenced, and someone tried to measure AC mains with phase on the negative input terminal (or something equally nasty), which is internal ground. Poof goes the resistor. Shouldn't have caused any other damage though, I think.

Then again, we all make dumb mistakes. Just last week I tried using a charger for a specific device. Wouldn't charge. Measured the output. 0V. It's rated for 230V range only but I'm on 100V - I could've sworn it worked on 100V even though it wasn't specced to (it's switchmode and not a chinese cheapie), but just in case I pulled out my step-up transformer. Nothing. Took it apart. Measured the output. 0VDC. Measured the input. 0VAC. Well, I had replaced the AC mains plug on this one, so take that apart, maybe one of the wires was loose. Nope, all solid. Then I turned on the power strip I was running this off of. Cue facepalm.

Well, at least I used this excuse to replace the mains plug again with a different style. Yes, I've lived in countries with 3 different kinds of AC mains plugs now. And sorry to break it to you, world, but European Schuko (the kind with a built-in safety shutter) and its unearthed Europlug variant is the best and most balanced home plug (and if you care about phase/neutral you're designing things wrong), American/Japanese 2-pin unearthed are the best travel plug (just because they're small and you can fit a bunch into a small power strip), the British design is an overengineered workaround for their shitty ring mains circuits and they need to stop pretending like the rest of the world hasn't figured out safety shutters yet, Ireland (where I have lived) is, as usual for Ireland, bass-ackwards in copying the British but then being more European (thus making the British design unnecessary with European wiring standards that don't require it), and I have no idea what you Aussies are up to but I haven't heard of any redeeming qualities for it. There, I said it 

[EEVblog]

Personally, though, as soon as I saw the creeping display and the correlation with changing ranges, I was thinking "faulty switches". But that's because I've seen a multimeter with a dodgy range switch do the same exact thing to me, so I'm lucky there (it was a cheapie chinese one, but the same principle applies). Experienced troubleshooters (especially of test equipment) will have the right hunches to save time, and you can't blame Dave for not having that. But knowing how to divide and conquer doesn't require experience, it's the basics, and I really feel that's where he messed up the procedure.

As I've said before, if I wasn't shooting the video and yapping, I probably wasted 5 real-world minutes worth of troubleshooting before I came to conclusion it was likely the switches. Bugger all really.

[EEVblog]

Well, Murphy or not, if you do eventually tackle these scopes PSU and processor boards, and you do some really careful, methodical step-by-step how-to videos covering the restoration process, I guarantee you that those repair videos will be some of your most popular.

Sorry, but nope, you'd be wrong.

[marcan]

As I've said before, if I wasn't shooting the video and yapping, I probably wasted 5 real-world minutes worth of troubleshooting before I came to conclusion it was likely the switches. Bugger all really.

Just because of the time it takes to shoot the video, or because it would've changed your process?

If it would've changed your process then that makes sense. Why though? Honest question here, does doing it as a video blog change the way you approach the problem? I'm not a video blogger so I wouldn't know, I'm curious.

But if you'd followed the same process then I feel you would've still wasted 15-30 minutes on the ADC; you did go through the trouble of checking datasheets and schematics and a bunch of passives around it after all. Not that it's the end of the world in time wasted anyway, and of course hindsight is 20/20 and the collective mob of the internet is always going to be better at everything than you are, so don't take it too seriously; just trying to offer some input here on what I think is the approach that would've saved some time.

[EEVblog]

Just because of the time it takes to shoot the video, or because it would've changed your process?

Both.

If it would've changed your process then that makes sense. Why though? Honest question here, does doing it as a video blog change the way you approach the problem? I'm not a video blogger so I wouldn't know, I'm curious.

It can, yes, even if just subconciously, as I've explained in previous posts in this thread.

But if you'd followed the same process then I feel you would've still wasted 15-30 minutes on the ADC; you did go through the trouble of checking datasheets and schematics and a bunch of passives around it after all.

I had the datasheets and other stuff printed in anticipation.
Actual testing would have taken maybe 5 minutes if I just followed that procedure.

just trying to offer some input here on what I think is the approach that would've saved some time.

Of course, thanks. And I'm just trying to explain to people why I may have done things the way I did. What makes it into the video is never the whole story.

[Tothwolf]

Well, Murphy or not, if you do eventually tackle these scopes PSU and processor boards, and you do some really careful, methodical step-by-step how-to videos covering the restoration process, I guarantee you that those repair videos will be some of your most popular.

Sorry, but nope, you'd be wrong.

Well, I could be wrong, but unless you give it a shot, we'll never know. 

I really do think there is demand for a series of repair videos for the 24x5 series scopes. Lately there have been pretty much daily discussions about repairing Tektronix 2465 and 2445 scopes on the tekscopes email list, and I'm not aware of anyone previously having done a comprehensive repair video series on them.

To clarify though, I wasn't saying that a 24x5 repair video would be your most popular video ever (the Solar Roadways videos were your most popular, weren't they?) but I do think a series covering the 24x5 scopes could over time become some of your more popular electronics repair videos...

If you are like me, your time is your most valuable commodity, so how about this...if it would help with eventually getting to the point where you could make videos about the 24x5 scopes, I'm willing to put in a few afternoons or whatever to help work up a parts list and source the parts needed for the PSU and processor boards (and if that works out and you get some functioning scopes, then the Tektronix-specific covers and mechanical parts).

I've got somewhere in the neighborhood of 300 to-do electronics repair/restoration projects of my own (those are just the ones I've put into a spreadsheet and filed parts bags for), but if you want to have David get in contact with me and send me some photos of the PSU and processor boards in your particular scopes (I have a 2465B, which will be similar to your scopes, but there were a number of different revisions of the boards), I'm willing to help with parts sourcing.

Anyhow, I think that's all I can really offer on the 24x5 scopes, so if it's still a "no" on the possibility of eventual 24x5 videos, and those two scopes are destined just to be non-functional background decoration forever, then I won't comment on them again.

[EEVblog]

Well, I could be wrong, but unless you give it a shot, we'll never know. 

After having created over 800 videos and spent 6 years watching the stats and reading every comment, I'm pretty confident it won't be worth the time and effort vs return for views. If that's all I was after of course.

I really do think there is demand for a series of repair videos for the 24x5 series scopes.
Lately there have been pretty much daily discussions about repairing Tektronix 2465 and 2445 scopes on the tekscopes email list, and I'm not aware of anyone previously having done a comprehensive repair video series on them.

I'm afraid that list amounts to a hill of beans in the scheme of views.
I have no doubt it would be popular amongst them, but to the general audience a series like that is not going to be hugely popular I'm afraid. Especially given the time and effort investment required, and the risk of it not working out well. I do not like committing myself to a series like that, and it is not my usual workflow nor style to work on videos in the background for months and then produced a polished repair video (that could be reasonably popular, but no more so than other repair videos).

If you are like me, your time is your most valuable commodity, so how about this...if it would help with eventually getting to the point where you could make videos about the 24x5 scopes, I'm willing to put in a few afternoons or whatever to help work up a parts list and source the parts needed for the PSU and processor boards (and if that works out and you get some functioning scopes, then the Tektronix-specific covers and mechanical parts).

Thanks for the offer but I'm afraid I cannot commit the time and effort required for this.
I have countless other videos and things I'd rather do instead of this, and ultimately for every video I do it comes down to motivation to do it, and as such a series like this barely registers on my interest list at present.
There is also so much I'd have to learn about Tek scopes in order to not look like a fool to the Tek repair email list crowd. I can't imagine the furore if I got some obvious things wrong.
And honestly, making a video for that kind of niche Tek fanboy crowd is like making a teardown video on a vintage *insert brand* computer. There are just so many people all too willing to scream that I got this and that wrong, I don't know squat about *insert brand* etc.  As a content producer I would not be honest if I said that kind of stuff doesn't sit in the back of my mind, and plays a part in the motivation required to do a video on something. It's not fear of course, it's one of motiviation.

If I thought the Tek scopes might be fixable fairly easily in a day then I'd of course have a shot at them. But my spidey sense tells me they won't be. And it might be well and good to "have a crack", I'd have to be willing to take the heat for potentially not finishing it, not producing follow-up's in timely enough fashion etc, like has happened with other videos.
Maybe I will, maybe I won't, but at this stage it's a no I'm afraid.

[Old Fart Analog Engineer]

Quote from Tothwolf
First, silver oxide is not an insulator. Silver oxide is very conductive and tarnished silver contacts by themselves are usually not a problem.

You are right, silver oxide is not an insulator, just a lousy conductor, and is the problem.  For those wanting to know how bad a conductor and why (CAUTION, heavy duty reading, links download PDFs): http://www.te.com/documentation/whitepapers/pdf/Ag_use_connectors_503-1016.pdf,  http://www.doiserbia.nb.rs/img/doi/1450-5339/2012/1450-53391200013C.pdf,  https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&cad=rja&uact=8&ved=0CEIQFjADahUKEwiAjPyJuZ3HAhWVNYgKHfRWAR4&url=http%3A%2F%2Fwww.mdpi.com%2F2075-4701%2F2%2F4%2F450%2Fpdf&ei=YwnIVcDOEJXroAT0rYXwAQ&usg=AFQjCNEU7_04rfokdHM8WGsHpIor1bs82w&sig2=IYjsAjjdZWOWEC2RQ4XWSA,

Quote from Tothwolf
Second, silicone grease should never be used anywhere near electrical switch and relay contacts. Western Electric / Bell System and others all learned this the hard way back in the day with their electromechanical telephone exchange switches. When used in or near switch contacts which interrupt current, any arcing can cause the silicone to break down into silicon-carbide,

"Dry" switching as in the Fluke meter, and other similar small small signal, low current or "logic" switching applications, involve perhaps nano Amps and do not "Arc" like 48 - 90+ volt into a nominal 600 Ohm load POTS telephone central office switches.

Quote from Tothwolf
(Older formulations of QD Electronic Cleaner contained Naphtha and Methanol instead of the Ethanol.)

According to CRC's currently posted Safety Data, sheet both are 60-80% Naptha.

The switches in the Fluke are not of the Schadow / Alps type, which have flat contacts.  They have round terminals and a unique moving contact which is much better than the flat Schadow terminals and moving contact.  The round post switches were originally from France and were distributed in the US by Centralab.  I designed audio test equipment in the 70's and used them extensively, but paid extra for the gold plating. Never had any issues (though after > decade of heavy use, the Gold eventually wore off).  If this type of switch has flat terminals, it will eventually fail.   In the 70's, Alps (Schadow's licensee) improved the moving contact's shape (added 3 contact dimples) and stiffened the springs because these were used by Pioneer and Harmon-Kardon Stereos and were noisily failing within two years in customers stereo receivers.  Pioneer even had a spare parts kit of the plungers with new contacts, all pre-greased with silicone grease as a repair part. 

I can't recall the French company's name and Google can't find it either.  If anyone knows, please tell me.  Thanks

OFAE

[ferdinandkeil]

I have a Keithley 177 that I got on eBay for next to nothing - of course it was acting up and I didn't come around to fixing it. So finally, after seeing this video I started working on it again, and what do you know, some contact cleaner later and now it's working on most ranges. So thanks a bunch 

I still have to figure out what's wrong with the 20 to 1000 V ranges. They all use the ÷10 circuit, so that's likely the culprit. I'm still pretty happy anyway as it's working just fine on the other ranges and appears to be still in cal.

Also props to MBY cleaning up the schematic 

[Tothwolf]

After having created over 800 videos and spent 6 years watching the stats and reading every comment, I'm pretty confident it won't be worth the time and effort vs return for views. If that's all I was after of course.

Of course. I'm sure some of it is also the fun that comes from making these videos and then seeing people enjoy them.

I'm afraid that list amounts to a hill of beans in the scheme of views.
I have no doubt it would be popular amongst them, but to the general audience a series like that is not going to be hugely popular I'm afraid. Especially given the time and effort investment required, and the risk of it not working out well. I do not like committing myself to a series like that, and it is not my usual workflow nor style to work on videos in the background for months and then produced a polished repair video (that could be reasonably popular, but no more so than other repair videos).

I agree that it might not be your usual off-the-cuff style, but occasionally mixing things up a little with a different or more complex repair project might work out pretty well too. I think most of your viewers (or at least those of us who have tackled these sort of projects) would understand that a video covering something like this would require some additional pre-planning.

What I was trying to suggest though is rather than going into it only with the expectation of a fully working scope at the end, is to break it down into individual sections, each of which can stand on its own. If at the very end (whenever that is) you wind up with a fully functional scope, all the better, but that doesn't necessarily have to be the end-goal.

For example, the single most common problem with these scopes is their PSU, which can be rebuilt and tested separately from the scope itself, so even if the scope has other problems, you could still tackle the PSU first in a standalone video. One community member has even been assembling dummy loads, and since you have two PSUs to potentially restore, something like that might be a worthwhile investment.

If either scope has the later processor board with the 4 small SMD electrolytics that leak, that could make for a video which covers the removal of those capacitors and repair of the board. If you already have a known working PSU, you might even be able to fold this into a video along with the Dallas NVRAM module issue and potential loss of cal data, if either of the boards have a Dallas module and the internal battery has died.

The same goes for the U800 horizontal amplifier IC (the large DIP package with the metal tab). Certain production versions of those chips suffered early thermal-related failures, but there is a good chance that your scopes do not even have this problem. If they did however, there are repair (155-0241-02 Re-Bake) and replacement options.

Anyhow...I'm probably going into way too much detail here, but you probably get the idea.

Thanks for the offer but I'm afraid I cannot commit the time and effort required for this.
I have countless other videos and things I'd rather do instead of this, and ultimately for every video I do it comes down to motivation to do it, and as such a series like this barely registers on my interest list at present.
There is also so much I'd have to learn about Tek scopes in order to not look like a fool to the Tek repair email list crowd. I can't imagine the furore if I got some obvious things wrong.

Unless you repair a specific widget regularly, it is basically impossible not to make at least one mistake. I think if you were to break the 24x5 scope restoration down into smaller parts though you'd find it really wouldn't be that bad.

And honestly, making a video for that kind of niche Tek fanboy crowd is like making a teardown video on a vintage *insert brand* computer. There are just so many people all too willing to scream that I got this and that wrong, I don't know squat about *insert brand* etc.  As a content producer I would not be honest if I said that kind of stuff doesn't sit in the back of my mind, and plays a part in the motivation required to do a video on something. It's not fear of course, it's one of motiviation.

Pfft...since when do you care what the fanboys think?

In all serious though, I get that. I also think the Tektronix community and other electronic test equipment communities would be very forgiving of any mistakes you might make since you don't service this stuff on a regular basis. No matter what sort of video you make, there are also always going to be a few Youtube trolls who will nitpick and scream.

If I thought the Tek scopes might be fixable fairly easily in a day then I'd of course have a shot at them. But my spidey sense tells me they won't be. And it might be well and good to "have a crack", I'd have to be willing to take the heat for potentially not finishing it, not producing follow-up's in timely enough fashion etc, like has happened with other videos.
Maybe I will, maybe I won't, but at this stage it's a no I'm afraid.

Yeah...they are definitely not a single day project from start to finish, but with enough prep work ahead of time, you might well be able to tackle the PSUs and stabilize/repair the processor boards (if your scopes have the later processor boards with those pesky SMD capacitors) in a single day.

In the end though, if you did restore the PSUs and processor boards and still had major problems with the scopes that just couldn't be overcome at all, you could always sell off both scopes to someone who could put more time into them and then reinvest in a fully restorable 2465B or 2467B...

Anyhow, you've got my email address if you ultimately change your mind. Overall though, I think you really are ahead of most with your two 24x5 scopes. They appeared to have all of their hybrid modules present (most of which are easy to remove since they are just held in with screws and nuts) and they still have all of their knobs (the small knobs almost always break when you try to pull them off, but I've come up with a way to repair them perfectly by solvent welding the plastic fingers back in).

PS, since I have your ear, any plans to have Doug back again anytime soon? I always seem to learn something new from those videos.

[EEVblog]

What I was trying to suggest though is rather than going into it only with the expectation of a fully working scope at the end, is to break it down into individual sections, each of which can stand on its own. If at the very end (whenever that is) you wind up with a fully functional scope, all the better, but that doesn't necessarily have to be the end-goal.

Yes, that's how I'd do it.

Anyhow, you've got my email address if you ultimately change your mind. Overall though, I think you really are ahead of most with your two 24x5 scopes.

One is an original and one is a B model though. I don't know how many parts are common.

PS, since I have your ear, any plans to have Doug back again anytime soon? I always seem to learn something new from those videos.

I've had a plan for a nice video involving Doug for a long time now. He's been very busy though. Will happen eventually.

[richfiles]

Man, that thing reminds me of the old HP 3466A (YES... Hewlett Packard, not Agilent, not Keyblahblah). It started giving me nonsensical readings... 

Wish I could get that puppy fixed, but I haven't had a chance to even consider what might have gone wonky. It's pretty much just like this meter, 4.5 digit, DC volts, AC volts, AC RMS volts, amps, and ohms, in all the same ranges, and even with the same DC only limitation on the low range... Except the HP 3466A is an auto-ranging meter with a battery option. It also has separate banana for amps, with a front accessible fuse.

Maybe I'll shoot some contact lube into the switches again... just incase! 

I imagine if it ain't that, this one will be a roller coaster of excitement. It has +/- 7 volt rails, +8 for battery charging, -2.6, +5, and +6.3, HP part numbers on chips. Fortunately though, the service manual does cross reference some of those to manufacturer part numbers such as CD40xx parts and Mxxxxxx parts. One chip is (I think), rather humorously cross referenced to it's own HP internal part number, and labeled as IC MISC NMOS. **dontbethatonedontbethatonedontbethatone 

I don't really know what to do with it. If I can fix it, I'd love to, cause the crappy DMM on my bench right now is a crummy 3.5 digit job that slides into one of those old Tektronix 500 series power units. The refresh rate on it is so slow, you can see it flicker, and it doesn't even show a proper over range on ohms when open, it just shoots to the max reading... Which is actually some arbitrary number, and not 1.999.

I kinda wanna fix my old Radio Shack meter too... Say what you will about transistor testers. I agree most are a gimmick, but this one had a beautiful one. 3 lead holes. That's it... It told you if you plugged an NPN or PNP, and then told you the order of the leads. Let me tell you, when you have to sub a transistor, that extra verification of lead order and transistor type, without needing to take the time to lookup datasheets... That was nice! I miss that meter, even if it wasn't the best. It had a very nice display too, going up to 3.999 (as opposed to 1.999), True RMS, a 40 step "analog" bar graph, and a few other basic features. Yeah, it's a cheapie, but it did the job for me when I didn't need the HP (remember, integrated rechargeable battery pack, for when it wasn't on the bench).

Now I have neither, and had to settle with an even crappier Rat Shack meter, as a holdover till I can replace ALL of it...

Should I mention the triggering is going on my old Tektronix T935A... 
Why me... 

[richfiles]

I'm actually unfamiliar with these Tek scopes that are being discussed, but considering the string of "busts" and easy repairs on all these recent test equipment repair videos... Heck, I'd watch that. 

[Tothwolf]

One is an original and one is a B model though. I don't know how many parts are common.

They share a lot of common parts. The PSUs might be slightly different revisions but would be interchangeable for testing. The processor board set in the 2465 is different from the processor board used in the 2465A and 2465B. The main board itself is different between each of the models, but many of the hybrid modules on the main board are the same and some could be swapped for testing if you had one that was suspect (the cal data wouldn't be correct of course).

From the mailbag video, it looks like your 2465B is pretty much identical to mine (the only real difference I can see is mine has the GPIB option board fitted). Your 2465B has the same late generation processor board as mine which has those nasty SMD aluminum electrolytics and the Dallas NVRAM module. Hopefully on your board they haven't leaked electrolyte down into that SMD variable resistor and surrounding circuitry. I lucked out in that my scope had been stored upright on end for a decade or more before I got it, and gravity appears to have kept any leaking electrolyte away from those areas of the board.

[Ampere]

As a beginner, it was nice to see someone going through the troubleshooting procedure from start to finish without already knowing what was wrong ahead of time. If you had already known what was wrong, it wouldn't have been as useful because it wouldn't really be troubleshooting video at that point -- just a video of you replacing a or fixing component. I don't think that it was an issue that the fault was actually mechanical. What's important is that you showed how to isolate the problem by showing what was NOT causing the fault.

Please do more repair videos in the future.

[Nerull]

"Meter hit with 30kV, stopped working" "Must be dirty switches!"

I must admit to being a bit skeptical of the psychic ability of many of the repair techs posting here.

[AF6LJ]

"Meter hit with 30kV, stopped working" "Must be dirty switches!"

I must admit to being a bit skeptical of the psychic ability of many of the repair techs posting here.

You can be skeptical as much as you like, many of us have been techs working in both repair and new gear for longer than some here have been alive.

If a piece of gear has a history of some part going bad that is usually the first place you look, especially if you are getting paid to fix said gear in a timely manner.

Also the person who sent Dave the meter didn't say it was hit with 30KV he said it was near a 30KV discharge. Which wouldn't have done anything to the meter in the first place.

As for the bridge and the blown resistor I have to go with the poster who suggested that someone tried to measure mains voltage with the meter and ended up with the negative test lead coming contact with the hot side of the mains.