Author Topic: Tektronix 465 Oscilloscope Troubleshooting (Read 20780 times)

DanielSpokane · « **on:** March 31, 2018, 04:35:37 am »

Does anyone have any experience trouble shooting a Tektronix 465 Oscilloscope? I picked one up for a steal at a flea market... it looks pretty clean, but I'm having a couple issues getting it going. The two issues that stand out are: 1) the trace is funky (non linear) w/ no signal (see pictures), and 2) the scope does not seem to recognize a probe/signal when hooked up to either channel (IE signal trace does not change (maybe a little but not much), the appropriate 5 or 50mv light does not come on corresponding to the probe, etc.). IE the signal trace is messed up and the scope is not changing/receiving a signal.

Any ideas?

tggzzz · « **Reply #1 on:** March 31, 2018, 08:33:24 am »

Don't bother thinking of alternatives until you have checked each of the many PSU rails to ensure both the voltage and ripple are within limits.

If not, then don't bother thinking of alternatives until you have rectified (ho ho) that.

Then use standard divide-and-conquer techniques, in combination with all the info in the service manual.

DimitriP · « **Reply #2 on:** March 31, 2018, 10:30:39 am »

Two things.
In your pictures both iinput coupling switches are set to GND. Set the input coupling to either AC or DC and try again.
That's was the good news .

If the trace changes shape as you are moving the vertical position up and down ..the CRT is damaged - probably-most likely

DanielSpokane · « **Reply #3 on:** March 31, 2018, 04:22:56 pm »

Thanks for the suggestions. I changed the coupling and used the probe and get indication that the probes are working. Does seem like maybe a screen or power supply problem.
I took a video of what it's doing including a couple adjustments.

https://www.youtube.com/watch?v=gSGErmCHR4M&feature=youtu.be

What do you think? I'm thinking maybe screen?

bd139 · « **Reply #4 on:** March 31, 2018, 04:34:14 pm »

Check power supply first. There are test points on the main board. They go absolutely mental and nothing works properly if the supply rails are out and this is the number one problem with them. I think 90%+ of the broken scopes I've seen from Tek are power supply issues. It's usually, at this age down to one of three things in priority order: (1) shorted tantalum capacitors, (2) knackered bridge rectifier, (3) knackered filter capacitors.

I've fixed a veritable ton of these now. Couple of reference threads for same line of scopes:

https://www.eevblog.com/forum/repair/tektronix-475-repair-assistance/

https://www.eevblog.com/forum/repair/tektronix-465b-repair-97327/

I'm using a 465 at the moment as well which was repaired.

DanielSpokane · « **Reply #5 on:** March 31, 2018, 08:11:23 pm »

Thanks for the ideas. I feel like I might be in a little over my head on this one... but I'm going to see what i can do.
I pulled the cover and turned it over to the power supply board. i tested the following test points:

TP 1423-- shorted and sparked and a light on the board turned on... and I didn't give me a voltage. Very weird.
TP 1486-- 43.3V
TP 1590-- 9.87V
TP 1594-- 8.79V

Below are a couple pictures from the manual. One is the board i tested and the locations of the above voltages. Following that is the schematic of the power supply. It seems weird that the test points shown on the adjustment layout does not show up on the schematic.

Still puzzling on next step.

DimitriP · « **Reply #6 on:** March 31, 2018, 08:16:09 pm »

Quote

What do you think? I'm thinking maybe screen?

Unfortunately it looks that way.
Here is a link to what's going on: https://entertaininghacks.wordpress.com/2016/03/09/rescuing-a-broken-tektronix-465-crt/

One the bright side, if that's the only thing wrong with it, "all you need" is a replacement CRT.

The way iit behaves, the trace will look it's best at the very top or bottom of the screen, so you should be able to veify the inputs and triggering are working.

bd139 · « **Reply #7 on:** March 31, 2018, 08:26:33 pm »

I doubt it’s that. Symptoms say otherwise.

That wasn’t a very good test run and inconclusive. The TPs you poked were mostly not power supply ones. The light on the board and the spark was you nearly zapping yourself on the HT. don’t poke anything around anywhere in the scope. There’s enough volts to kill you instantly in a few places.

Check the following TPs and let us know the voltages.

TP1568
TP1558
TP1548
TP1536
TP1518

Do these relative to the one marked ground on the middle of the board.

Be careful. This is a dangerous bit of kit. Highest test point voltage there is 110 volts which will wake you up if you’re not careful. Do each one carefully and methodically.

tggzzz · « **Reply #8 on:** March 31, 2018, 08:39:14 pm »

Quote from: DanielSpokane on March 31, 2018, 08:11:23 pm

It seems weird that the test points shown on the adjustment layout does not show up on the schematic.

There are many schematics; you haven't found the right one.

With Tek, Rxxxx is physically and logically close to Cxxxx and TPxxxx etc. That should give you pointers.

DimitriP · « **Reply #9 on:** March 31, 2018, 08:42:35 pm »

Quote

I doubt it’s that. Symptoms say otherwise.

Doubting is free.
Having seen and replaced a crt with a bad mesh in real life ...priceless.

tggzzz · « **Reply #10 on:** March 31, 2018, 08:48:11 pm »

Quote from: DimitriP on March 31, 2018, 08:16:09 pm

Here is a link to what's going on: https://entertaininghacks.wordpress.com/2016/03/09/rescuing-a-broken-tektronix-465-crt/

The OP's scope isn't casting shadows on nearby walls, therefore the grid connection isn't broken.

The strange looping in the traces may be due to a bent mesh (as in those pictures), or even due to some crud on the mesh. In one CRT small loops suddenly appeared on the screen; shaking the CRT moved the crud on the mesh elsewhere in the CRT (for a while, at least).

bd139 · « **Reply #11 on:** March 31, 2018, 08:53:07 pm »

Yes definitely not grid. Those tubes are stupid bright when that goes.

I’ve seen these patterns when the front end FET gate resistor broke off a 475 before as well. It was so high impedance it went mental.

DanielSpokane · « **Reply #12 on:** March 31, 2018, 08:53:30 pm »

I was careful and took readings on the following test points:

TP1568 -- 8.09V
TP1548 -- 12.87V
TP1536 -- 55.9V
TP1558 -- 5.08V
TP1518 -- 110.07V

Thoughts?

bd139 · « **Reply #13 on:** March 31, 2018, 08:56:56 pm »

TP1548 is low. This should be around 15V. Check capacitor C1549. Should be a big blue tantalum one towards the middle of the unit.

Unplug the unit, give it a couple of minutes and measure the resistance across it. If it’s less than about 50 ohms, snip one lead of that capacitor off at the base of the capacitor and power it up again and see what happens. Measure the voltage at TP1548 again. If it is 15v and the scope works then desolder it and stuff a 100uF 25V electrolytic or better in there. If it isn’t, post back

DimitriP · « **Reply #14 on:** March 31, 2018, 09:05:30 pm »

Quote from: bd139 on March 31, 2018, 08:53:07 pm

Yes definitely not grid. Those tubes are stupid bright when that goes.

I’ve seen these patterns when the front end FET gate resistor broke off a 475 before as well. It was so high impedance it went mental.

I'll just wait..the bad mesh not going anywhere ....

bd139 · « **Reply #15 on:** March 31, 2018, 09:08:38 pm »

That’s completely different to the OP’s traces. And yes that’s a knackered tube.

DanielSpokane · « **Reply #16 on:** March 31, 2018, 09:13:02 pm »

The resistances across C1549 is 174ohms.

bd139 · « **Reply #17 on:** March 31, 2018, 09:14:09 pm »

Was it a blue tant (square one)?

DanielSpokane · « **Reply #18 on:** March 31, 2018, 09:18:45 pm »

Not sure how to identify a blue tant. See picture. It is the yellow/purple one located next to the test points.

DanielSpokane · « **Reply #19 on:** March 31, 2018, 09:43:05 pm »

At 174ohms that is not terribly far from 50ohms. Should I clip and measure?

bd139 · « **Reply #20 on:** March 31, 2018, 09:46:39 pm »

Sorry for delay was checking service manual. That is probably first step yes. It's the striped one in the middle. You can also desolder one leg as an alternative or if you don't have a replacement part handy.

You might have to do a few of these before you find it.

Yours is later than mine is and has the newer capacitors in it (also unreliable!). That cap is almost universally the first cap that goes wonky. There's another one under the HT shield but your CRT is displaying a trace so that's fine at the moment.

When you replace it later, remove the screw or it'll sink all the heat into the chassis and it'll be impossible to clean up the holes.

DanielSpokane · « **Reply #21 on:** March 31, 2018, 09:57:54 pm »

I desoldered one leg of the cap and turned on the scope and tested TP1548 and it is still 12.8V. I tried to measure capacitance across the capacitor and can't seem to get a reading. I measured resistance across it and it changes, etc. typical of a capacitor.

Appreciate the help!

bd139 · « **Reply #22 on:** March 31, 2018, 10:07:00 pm »

Gah this one is going to be difficult then.

Next step is a visual inspection of all capacitors on all the boards. Look for cracked or burned tantalum capacitors that look the same as that one. They may be present on any of the four boards in the scope. The timebase one is difficult to see but there's one on that you can observe if you look top down. I use a plastic ruler and move it across in inch steps then scan from left and right to find them all and inspect.

If you can't find anything obvious then the next steps are:

1. Check for an AC voltage on the TPs listed before. You can probably get away with a DMM on AC volts for this but another oscilloscope is better. This will identify any problems in the left half of the power supply (rectifiers, smoothing caps, voltage regulators). If that looks ok, i.e no AC voltage registered, proceed to...
2. Finding all tantalum capacitors on the 15V rail and testing them.

I have had to do a wholesale replacement process on the entire scope before. Takes a while but is worth it.

Once this is reading 15V, diagnostics may proceed. The problem as always with these is that everything depends on this being spot on.

DanielSpokane · « **Reply #23 on:** March 31, 2018, 10:35:15 pm »

I looked at all the tant caps and the only one that looked like it had a small hairline crack is C1113 on the timing circuit board (see picture). No burnt looking caps that I could see.

Also, I checked for AC on the test points. Found the following:

TP1568 -- DC 8.09V -- AC 115mV
TP1548 -- DC 12.87V -- 3.03V
TP1536 -- DC 55.9V -- 0.77V
TP1558 -- DC 5.08V -- 184mV
TP1518 -- DC 110.07V -- 0.72V

bd139 · « **Reply #24 on:** March 31, 2018, 11:30:25 pm »

Ok desolder one leg of that. That’s a blue tant of doom. Crack is suspicious and that board has 15v rail.

It’s 00:30 here so going to bed now. Will check back in morning.

tautech · « **Reply #25 on:** March 31, 2018, 11:34:32 pm »

Quote from: DanielSpokane on March 31, 2018, 10:35:15 pm

I looked at all the tant caps and the only one that looked like it had a small hairline crack is C1113 on the timing circuit board (see picture). No burnt looking caps that I could see.

Also, I checked for AC on the test points. Found the following:

TP1568 -- DC 8.09V -- AC 115mV
TP1548 -- DC 12.87V -- 3.03V
TP1536 -- DC 55.9V -- 0.77V
TP1558 -- DC 5.08V -- 184mV
TP1518 -- DC 110.07V -- 0.72V

The 15, 12 and 5V rails all have excessive ripple IMO.
Check the service manual for the listed max ripple limits.

Something's still pulling the 15V rail down and when that happens and the rail is under stress, ripple measurement rises. Get the 15V rail roughly to spec first before looking at anything else.....other stuff can wait.

DanielSpokane · « **Reply #26 on:** April 01, 2018, 02:41:47 am »

Late night for you bd139

Thanks for the help! Thanks everyone else too!

I pulled one leg of C1113 and tested the 15V TP and it reads 12.7V. Hnmm... any ideas on a next step?

Also, I have a couple caps from a parts radio. They are 100uf 50V. See attached pictures. You think I should replace either C1549 or C1113 with these?... both still have one leg of the orignial cap pulled. I can put back the leg or use these.

DanielSpokane · « **Reply #27 on:** April 01, 2018, 03:23:17 am »

tautech, following are the typical ripple specs. Yes, mine appears to be out of spec. Hopefully if I can get the 15V power supply in spec that will help.

From Table 6-4--Typical Ripple
+55V @ TP 1536 = 4 mV
+15V @ TP 1548 = 2 mV
+5V @ TP 1558 = 2 mV
-8V @ TP 1568 = 2mV
+110V @ TP1518 = 20mV

tautech · « **Reply #28 on:** April 01, 2018, 03:34:28 am »

Quote from: DanielSpokane on April 01, 2018, 03:23:17 am

tautech, following are the typical ripple specs. Yes, mine appears to be out of spec. Hopefully if I can get the 15V power supply in spec that will help.

From Table 6-4--Typical Ripple
+55V @ TP 1536 = 4 mV
+15V @ TP 1548 = 2 mV
+5V @ TP 1558 = 2 mV
-8V @ TP 1568 = 2mV
+110V @ TP1518 = 20mV

Dan, also understand that the rails can be referenced a just one of the rails therefore adjustments can be interlinked.
But for now just get the ones that are way off somewhere near where they should be to see if normal operations return.

Listen to what bd139 says about these, he knows his stuff.

bd139 · « **Reply #29 on:** April 01, 2018, 07:28:40 am »

Those replacement caps are fine. I wouldn’t put the old ones back in because they are guaranteed to fail in the future. Best to find the actual dead one first. Next step is to either trace all the caps on the 15v rail with the schematics. This is a long job unfortunately. Print out all the schematics and circle them all. They are usually labelled up next to the 15v supply. Then go round and check them all.

As tautech says, all bets are off until that rail is sorted.

Ripple isn’t terribly important to start with. The scope will work with high ripple just the triggering will be dicky and the traces will have a lot of noise on them.

Edit: just a point before I forget. Probably worth looking at the ripple before the regulator as well now. The 15v rail will drop out if it’s not seeing enough volts in as well. If half the bridge rectifier is fluffed or the filter cap is dying it will result in poor regulation.

Do you have another scope?

DanielSpokane · « **Reply #30 on:** April 01, 2018, 08:15:02 am »

Sounds good. I'm going to head to bed now (it's 1AM here) but will do this tomorrow. I will print off copies and make sure to check all capacitors touching the 15V rail. I assume I just lift one leg and test to see if the 15V rail goes from 12.7V to 15V?... if not, then I go to the next one?

Yes I do have another oscope. I have a Siglent SDS 1102X.

Thanks again

tggzzz · « **Reply #31 on:** April 01, 2018, 08:32:31 am »

If the input to a regulator is OK but the output is too low, then there is probably excessive current being drawn somewhere.

A IR camera (or even thermometer) might conceivably help indicate hotspots.

Excess current will cause larger voltage drops along PSU rails. Careful measurement of differential voltages along a PSU track can sometimes help indicate where the current is going. Use a DVM on mV range.

Read the manual to see which PSU rails depend on the regulated 50V rail. Some of them are simply a fixed proportion of that voltage, so if the 50V is X% low then such rails will also be X% low.

bd139 · « **Reply #32 on:** April 01, 2018, 08:34:30 am »

Cool. That’s all you have to do yes.

Worth popping a scope on the collector of Q1544 first and seeing what the lowest voltage is before you do this. If this is close to or lower than 15V it will cause regulation loss. At that point C1542 or CR1541 are suspect. Sometimes on these, the capacitor goes high ESR and blows one or more diodes in the bridge rectifier after which it limps.

If you can, also post a picture of the waveform at TP1548 (15v out). This should result in some clues.

There is a possibility that the 55V rail, from which everything is referenced from is misbehaving.

tautech · « **Reply #33 on:** April 01, 2018, 09:07:48 am »

Quote from: DanielSpokane on April 01, 2018, 08:15:02 am

Yes I do have another oscope. I have a Siglent SDS 1102X.

Simple to take screenshots with but you'll have to compress them or change then to another format so that they're smaller than the 1MB/file forum limit.

DanielSpokane · « **Reply #34 on:** April 01, 2018, 03:14:36 pm »

Good morning (at least here anyway) and happy Easter

Below is TP 1548 from the scope.

At Q1544 there are 3 leads. Should I scope each of them?

tautech · « **Reply #35 on:** April 01, 2018, 03:28:40 pm »

Quote from: DanielSpokane on April 01, 2018, 03:14:36 pm

Good morning (at least here anyway) and happy Easter

Below is TP 1548 from the scope.

At Q1544 there are 3 leads. Should I scope each of them?

With 6V+ ripple I'd be looking hard at C1552.

Also:

Quote from: DanielSpokane on March 31, 2018, 10:35:15 pm

Also, I checked for AC on the test points. Found the following:

TP1568 -- DC 8.09V -- AC 115mV
TP1548 -- DC 12.87V -- 3.03V
TP1536 -- DC 55.9V -- 0.77V
TP1558 -- DC 5.08V -- 184mV
TP1518 -- DC 110.07V -- 0.72V

The DC value is close enough to agree but the AC not.

tggzzz · « **Reply #36 on:** April 01, 2018, 04:09:52 pm »

Quote from: DanielSpokane on April 01, 2018, 03:14:36 pm

Below is TP 1548 from the scope.

At Q1544 there are 3 leads. Should I scope each of them?

120Hz => the bridge rectifier diode CR1541 is OK.

I'll bet the flat top is somewhere near 15V, indicating the 15V regulator is working OK. The action of the regulator is to try to keep the voltage at TP1548 the same as the "reference" at the junction of R1543/R1544. It not be 15V if either the input voltage (C1542) drops too low or the reference falls. The reference voltage is simply a fraction of the 55V rail (TP1536).

So, if TP1536 looks OK, then look at the reference voltage, then look at the +ve of C1542 which is the "input" to the 15V regulator.

Quick dirty test to see if C1542 is kaput: temporarily solder a "similar" capacitor across C1542 and see if it makes a difference to the waveforms. "Similar" means adequate voltage, and capacitance not much greater (to avoid excessive inrush current) and not too much smaller. If value is 10% of C1542, then very crudely expect a 10% improvement in ripple.

Caution: the C1542 terminals are close together and could be shorted easily. Keep your scope probe's ground lead well away from that area, since if it touched a non-zero voltage there could be sparks followed by sighs.

DanielSpokane · « **Reply #37 on:** April 01, 2018, 06:51:47 pm »

Looking at C1552 and C1542 they are both larger power capacitors mounted to the reverse side of the board. Are you thinking I should solder a capacitor to the bottom side (the visible side) of C1552 and hook my scope up to TP1548 and see if there is any improvement to the ripple? I assume the capacitor should be electrolytic with voltage rating exceeding say 25Volts or so? Any suggestion on the uF rating for this test cap?

tggzzz · « **Reply #38 on:** April 01, 2018, 07:10:26 pm »

Quote from: DanielSpokane on April 01, 2018, 06:51:47 pm

Looking at C1552 and C1542 they are both larger power capacitors mounted to the reverse side of the board. Are you thinking I should solder a capacitor to the bottom side (the visible side) of C1552 and hook my scope up to TP1548 and see if there is any improvement to the ripple? I assume the capacitor should be electrolytic with voltage rating exceeding say 25Volts or so? Any suggestion on the uF rating for this test cap?

It is a temporary connection to see if the existing capacitor is duff, so make connections any place convenient. Yes, that is probably directly across the end of the terminals that are visible without removing the PCB - and you probably won't be able to put the case on at the same time! (Since you are a beginner, I won't suggest you simply hold a capacitor and touch the leads to the live circuit!)

What's the voltage rating of the existing capacitor? Any parallel capacitor should have the same or higher voltage rating.

Have a look in the manual at the tolerance of the capacitance value: that will give a hint a wide range is acceptable. For the test (cf normal operation) the capacitance is uncritical. The larger the capacitor the easier to see the effect of having a good capacitor. Even if the capacitor is only 10% of the nominal value, you should see some difference; how much difference will depend on how bad the existing capacitor is. But don't use a much higher capacitor value, since the inrush current might be too high. So, start with whatever caps you have to hand, say 10% to 100% of the nominal value.

If you identify problem capacitor(s), you will have to replace them with appropriate alternatives. Removing those caps is a pain, and you'll probably need "adaptors" to match the footprint, but that is a problem for later.

DanielSpokane · « **Reply #39 on:** April 01, 2018, 09:20:58 pm »

According to the manual C1552 is rated at 5000uF at 25V. I looked through my stash and the best I have are the following:

1. 100uF at 50V
2. Sprague powerlytic 36D8084--17000 at 25VDC

Seems like one is too small the other too big?

Also, see picture below. I shined a light behind the board to see where the caps are in relation to the solder points. Looks like there are 3 solder points per cap.

JDubU · « **Reply #40 on:** April 01, 2018, 09:36:56 pm »

Here's Jim Williams fixing a Tek 465 (spoiler alert: shorted tantalum cap).

tautech · « **Reply #41 on:** April 01, 2018, 09:41:22 pm »

Quote from: DanielSpokane on April 01, 2018, 09:20:58 pm

Seems like one is too small the other too big?

Yep but you could try 2x 100's paralleled and tacked on the correct pads......just be sure you get the polarity and position right ! (extender leads permitted)

Then without any other changes look for an improvement in the ugly sawtooth waveform and grab us a screenshot.
Take your time.....and no mistakes !

tggzzz · « **Reply #42 on:** April 01, 2018, 09:47:29 pm »

Quote from: DanielSpokane on April 01, 2018, 09:20:58 pm

According to the manual C1552 is rated at 5000uF at 25V. I looked through my stash and the best I have are the following:

1. 100uF at 50V
2. Sprague powerlytic 36D8084--17000 at 25VDC

Seems like one is too small the other too big?

Also, see picture below. I shined a light behind the board to see where the caps are in relation to the solder points. Looks like there are 3 solder points per cap.

What is the sprague's capacitance?

The existing cap has several can connections plus one other. Look at the schematic and trace out the PCB connections.

Use what you have available.

DanielSpokane · « **Reply #43 on:** April 01, 2018, 10:01:27 pm »

The Sprague's capacitance is 17000... I believe. It is big... about half the size of a soda can. The other option is to do as suggested and pair a few spares in parallel and see how much I can add up. ... or order something.

DanielSpokane · « **Reply #44 on:** April 01, 2018, 10:50:50 pm »

Think there is any harm in doing the 17,000uF test cap?

tautech · « **Reply #45 on:** April 01, 2018, 10:56:41 pm »

Quote from: DanielSpokane on April 01, 2018, 10:50:50 pm

Think there is any harm in doing the 17,000uF test cap?

I wouldn't for only one reason:
Inrush current could damage the bridge rectifier diodes. Their design is such that they only expect to charge 5kuF in however many mains cycles it might take.....times that by 3 and you put some serious load on those diodes......maybe more than they can manage.
Is it worth the risk ? IMHO NO !

bd139 · « **Reply #46 on:** April 01, 2018, 10:59:07 pm »

Those bridge rectifiers are pretty fragile. I've had a couple of dead ones. They're also difficult to get out.

I wouldn't risk it. I have a couple of 2200uF 35v ones floating around I use for these sorts of things.

DanielSpokane · « **Reply #47 on:** April 02, 2018, 12:05:05 am »

Ok, sounds good, I'll hold off on the 17K

I'll parallel up a few caps and connect to C1552 and will post a picture when I'm done. Any other suggestions?

bd139 on Q1544... which leg is the collector? I'll put a scope on that too. Sorry I'm not totally familiar with all the terminology. Learning as I go

tggzzz · « **Reply #48 on:** April 02, 2018, 12:12:38 am »

Quote from: DanielSpokane on April 02, 2018, 12:05:05 am

bd139 on Q1544... which leg is the collector? I'll put a scope on that too. Sorry I'm not totally familiar with all the terminology. Learning as I go

Don't: you could easily short pins together or pull pins from the socket. Put the probe on something connected to the collector.

tautech · « **Reply #49 on:** April 02, 2018, 12:18:02 am »

Quote from: DanielSpokane on April 02, 2018, 12:05:05 am

I'll parallel up a few caps and connect to C1552 and will post a picture when I'm done. Any other suggestions?

None, just one definitive step at a time at this stage while you become more familiar with the scope and its workings.

DanielSpokane · « **Reply #50 on:** April 02, 2018, 02:38:15 am »

Ok I'm looking over the schematic and I'm thinking I want to add the capacitors in parallel to C1542 not C1552. Right? C1542 looks like it is in power supply for the 15V rail. For some reason I was thinking C1552... but that is on the 5V PS. Correct?

Also, after I connect this... I assume I'm still taking the scope reading at TP 1548 and compairing to the funny looking output I posted earlier to see if the ripple dispoates which maybe points to C1542 as as the cuplrit (in part at least)?

tautech · « **Reply #51 on:** April 02, 2018, 03:07:54 am »

Quote from: DanielSpokane on April 02, 2018, 02:38:15 am

Ok I'm looking over the schematic and I'm thinking I want to add the capacitors in parallel to C1542 not C1552. Right? C1542 looks like it is in power supply for the 15V rail. For some reason I was thinking C1552... but that is on the 5V PS. Correct?

Also, after I connect this... I assume I'm still taking the scope reading at TP 1548 and compairing to the funny looking output I posted earlier to see if the ripple dispoates which maybe points to C1542 as as the cuplrit (in part at least)?

You're onto it.

Now a few clues about that screenshot.
Frequency = 2x mains
From Trigger level box; trig level plus ~2 div = ~15V where the flat top was and where the regulator was holding it to 15V. The sawtooth was typical 'pre' regulation and the degree of ripple tells us the main filter cap is not doing its job.

The blue trace is what it should look like after the cap and the min amplitude = Vreg + 0.7 to allow for the diode drop in the pass transistor.

DanielSpokane · « **Reply #52 on:** April 02, 2018, 04:03:49 am »

Wow, that graph is very helpful. Thank you!

I paralleled 600uF to C1542 (using (3) 200uF caps I found stashed away). I fired up the scope and the voltage at TP 1548 now reads 15.4V. I posted the scope output and a picture of the test setup (for fun). It looks like DC voltage is right and the rectified power looks correct (best i can tell).

I also took a video of the scope screen while this is occurring. The trace is now linear and looks very nice (I did a little adjusting after the video and it looks even better). A video of it is at:

Looks like I need to replace C1542... and then recheck everything? Any suggestions on replacement technique and cap to use?

tautech · « **Reply #53 on:** April 02, 2018, 05:18:32 am »

Great !

Now we back up some and recheck all the other rails for accuracy and ripple and decide how many other main smoothing caps need attention. All rails must meet the Tek spec for ripple. Levels we can adjust later.

The manual BOM will have the specs for each cap and when making a selection for this older gear be sure not to pick anything with too low ESR.....it only adds to the diode surge current at power ON.
Chris (bd139) will know where he gets them from but you're on the other side of the pond so I guess your best bet is Digikey or maybe check Tedds:
https://www.tedss.com/

You'll probably need to pull C1542 to measure the pinout and mounting lug layout but these 'cans' can be difficult to get so you might have to 'shoehorn' a radial in there instead.
Again, bd139 will know as he's done plenty of these over the years.

So recheck the others, build a list and park it until you get replacement/s sorted.

DanielSpokane · « **Reply #54 on:** April 02, 2018, 05:52:23 am »

Awesome! I will wait and see what bd139 has to say regarding suggested cap.

I checked voltages again w/ the 600uF in parallel with C1542:

TP1568 -- DC 8.11V -- AC 1.4mV
TP1548 -- DC 15.28V -- AC 1.2mV
TP1536 -- DC 56.0V -- AC 1.5mV
TP1558 -- DC 5.09V -- AC 1.5mV
TP1518 -- DC 110.07V -- AC 2.5mV

All appear to be within spec.

bd139 · « **Reply #55 on:** April 02, 2018, 07:57:52 am »

Looking good.

Two options for replacing that cap. One nice and one not so nice.

First step is to get the thing out which is a nightmare. I use desolder braid and a 50W Weller and it’s hard work.

There are three terminals and two are shorted. They need to be shorted on the scope as well as I think if I remember correctly it bridges two parts of the circuit. New capacitors are tiny compared to the originals so your options are usually getting one in as best as possible via lead bending and then jumping the other two pins on the bottom of the board.

The last one I replaced however i made a carrier board. I took a piece of scrap FR4 PCB offcut, cut it into a circle with aviation shears, marked the original pins on, gouged out a channel to separate negative and positive, drilled holes for the new cap and old pins and the used snipped off 2W resistor leads to jump this board. Didn’t take any photos however

As for the cap, I tend to use Vishay, rubycon or Epcos ones for this job but to be honest any brand cap will do. Forget looking for an original can - they’re stupid expensive ($50+ each!). Make sure it’s 105oC rated, voltage is higher than the peak voltage and that’s about it. If you’re feeling sneaky, measure the lead pitch of two of the holes on the board and order one that fits. Don’t get low ESR ones.

To quote Wes Hayward, it doesn’t need to look good to work good.

tautech · « **Reply #56 on:** April 02, 2018, 08:00:13 am »

A few possible options I found while having a look around but most seem to be low ESR

http://nz.element14.com/vishay/mal205016472e3/cap-alu-elec-4700uf-25v-solder/dp/1166572
https://nz.rs-online.com/web/p/aluminium-capacitors/4340699/
https://www.tedss.com/2020038380
https://www.digikey.co.nz/product-detail/en/vishay-bc-components/MAL205156472E3/4778PHBK-ND/5632831

bd139 · « **Reply #57 on:** April 02, 2018, 08:08:36 am »

That last one is interesting the MAL205156472E3. Worth checking the pin pitch on the data sheet.

Still 4x the price of the ones I use though

tautech · « **Reply #58 on:** April 02, 2018, 08:14:24 am »

Quote from: bd139 on April 02, 2018, 08:08:36 am

That last one is interesting the MAL205156472E3. Worth checking the pin pitch on the data sheet.

Still 4x the price of the ones I use though

http://www.vishay.com/docs/28346/051053pe.pdf

Remember your Pound is ~1/2 our NZD

bd139 · « **Reply #59 on:** April 02, 2018, 08:20:22 am »

Yeah true. The one is pick is about £2 including delivery from RS though

tautech · « **Reply #60 on:** April 02, 2018, 08:28:45 am »

Quote from: bd139 on April 02, 2018, 08:20:22 am

Yeah true. The one is pick is about £2 including delivery from RS though

Here's a cheaper selection but few of which I'd consider worthy of putting in a Tek PSU.

https://nz.rs-online.com/web/c/passive-components/capacitors/aluminium-capacitors/?applied-dimensions=4294826632,4294518902,4292338771,4294885341&pn=1

Addicted2AnalogTek · « **Reply #61 on:** April 02, 2018, 08:29:31 am »

You could go fancy with it and order some cap adapter boards (courtesy of Dave K). I ordered some just to have, and recently replaced a couple of caps in my 465B using them. "CAPBOARD_S_v2.zip" are the files for the caps with 3 ground pins (the ones you would use) , and the "L" is for the larger caps that have 4 ground pins.

https://www.eevblog.com/forum/repair/making-dave_k's-capacitor-adapters-at-osh-park/

I went a bit overkill on the caps and used these:

https://www.mouser.com/ProductDetail/EPCOS-TDK/B41252B7568M000?qs=sGAEpiMZZMtZ1n0r9vR22flQyDdOCPao7Ig0dxc2YlI%3d

bd139 · « **Reply #62 on:** April 02, 2018, 08:40:49 am »

Those are really neat but I couldn’t be bothered with that hence why I snipped my own out of FR4 stock

... I might be tempted if I ever get my hands on a high end 7000 series.

Good choice on capacitor. Epcos ones are really nice.

Addicted2AnalogTek · « **Reply #63 on:** April 02, 2018, 09:03:52 am »

I can see why you wouldn't bother to go that route on a 400 series... one small board costs a little over 2 USD shipped from OSHPARK, and you have to buy at least 3. Next, wait about two weeks. I bought the recommended pins from Mouser at $0.24 each (x4 necessary for each board) IIRC. Then you still need to pay for the capacitor and shipping. It just doesn't make sense unless you're placing large orders and don't mind buying boards for possible future use, not to mention waiting weeks for the boards.

Buying all of that to restore a high end 7xx4 scope... yes, definitely! I wish I would have grabbed that 7844 option 4/78.... oh well.

bd139 · « **Reply #64 on:** April 02, 2018, 09:26:57 am »

OSHpark always takes over a month for me. I’ve moved to JLCPCB. You can get ten 4x4” boards for $15 shipped! Reckon your could get 4 per board so 40 for $15

DanielSpokane · « **Reply #65 on:** April 02, 2018, 03:44:59 pm »

Thanks for all the help everyone. I'm at work now, but tonight I will pull the capacitor and will review dimensions. I like the idea of making a carrier board. I will give that some thought tonight as well. Regarding the cap size... looks like several of the caps suggested are 4700uF. Since the original is 5000uF... I assume that is close enough? Also, what value would you consider low ESR?

Regarding the cap adapters... what file format are those files in? I have AutoCAD but it doesn't look like a typical AutoCAD format.

Another idea I was thinking about is connecting wire leads to each of the 3 cap pins (using a crimp or friction type connection) and then working the wires through the holes pulling tight and clipping. Easier said than done?

Thanks again!

DanielSpokane · « **Reply #66 on:** April 02, 2018, 04:30:27 pm »

Quote from: Addicted2AnalogTek on April 02, 2018, 08:29:31 am

I went a bit overkill on the caps and used these:

https://www.mouser.com/ProductDetail/EPCOS-TDK/B41252B7568M000?qs=sGAEpiMZZMtZ1n0r9vR22flQyDdOCPao7Ig0dxc2YlI%3d

Do you know off hand if the diam. is ok for this cap? I haven't pulled mine yet and am at work so can't measure right now. But... I'm order some mouser parts and was thinking about including this.

bd139 · « **Reply #67 on:** April 02, 2018, 05:29:09 pm »

4700 is probably ok. The capacitor usually specifies a tolerance. If it’s -20 to +80% on the service manual, make sure the new capacitor matches or exceeds that and it will be ok.

Size, no idea. The new ones are usually only 18mm which is much smaller than the originals.

Addicted2AnalogTek · « **Reply #68 on:** April 02, 2018, 06:32:51 pm »

@ bd139: Thanks! I may place an order from JCLPCB for some 7K adapters in anticipation of the need to change some caps in my 7854. The ones I got from OSHPARK are A+ quality, so I'd like to compare them, anyway.

@ Daniel: OD of the cap can be no more than 30mm. Even that is a squeeze, so I would go 28mm or less diameter. Obviously, you'll never find longer caps than the OEM, so any length will do.

The manual states 5000uf -0%/+100% 25V (C1552) and 5500uf -10%/+100% 30V (C1542), so I chose 5600uF to replace both the 5000uF and 5500uF, which worked fine for me. I tend to aim for slightly higher voltage rated caps, so I originally chose the following 63V rated, which are 30mm diameter and barely fit:
https://www.mouser.com/ProductDetail/871-B41252A8568M000

The ones I posted ~~above~~ previously seem ideal for replacing either, and are 5600uF 35V and 25.4mm diameter. Just purchase ones that aren't stated in the datasheet to be "low ESR". You also want ones that are designed for SMPS or line filtering, which you'll be able to tell easily by the stated "test frequency" on the datasheet. If you click the link and scroll down, you'll notice that it states "Test Frequency: 120Hz". Another indicator for this is that the datasheet will state under "Applications" that they are for ideal for power supplies.

If you want to be quick about it, you could just solder some insulated wires to the capacitor terminals (with some heat shrink tubing over the exposed conductor), feed those through their respective holes, and then bridge the 3 ground holes together with more wire. The original caps are metal cans, so all three of the grounding holes are connected in the original design. You could just zip-tie the new cap to one of the original ones if you so choose, and it will work fine. Myself, I prefer to have the new cap firmly attached to the main board, though.

MarkL · « **Reply #69 on:** April 02, 2018, 08:07:22 pm »

Quote from: DanielSpokane on April 02, 2018, 03:44:59 pm

...
Regarding the cap adapters... what file format are those files in? I have AutoCAD but it doesn't look like a typical AutoCAD format.
...

If you mean CAPBOARD_L_v2.zip and CAPBOARD_S_v2.zip from the other thread, those are Gerber files plus the TXT file is a drill file, ready for submission to your favorite PCB manufacturer. You can use any Gerber viewer to look at them.

Addicted2AnalogTek · « **Reply #70 on:** April 02, 2018, 08:21:36 pm »

Ah yes, thanks MarkL, I forgot to address that.

I'm familiar with OSHPARK so I'll explain it for that website.

After you download the capboard gerber files, all you need to do is open OSHPARK website, click "browse for files". Next, access the folder you downloaded the files to and select "CAPBOARD_S_v2.zip". That's it! You don't need to worry about the warning it will give for the lack of a bottom silk screen.

It's probably very similar on the other PCB manufacturer's sites.

The mounting pins that I used, as recommended, are "Harwin (p/n H2101-01)", which are available from Mouser. Those fit nicely into the smaller holes on the 465's main board. However, I noticed that in order to have proper clearance between the capacitor leads and the main PCB, I had to solder them to the adapter board without them being fully inserted into the adapter board.

DanielSpokane · « **Reply #71 on:** April 03, 2018, 04:23:36 am »

Thanks for all the explanation. Very helpful. I ordered the EPCOS 5600uF 35V Ecap... actually I ordered 2 just incase the other goes bad at some point... that and I love to stockpile haha

I'm getting ready to take this cap out and the best i can tell there are 4 connection points. See picture below. Looks like 1, 2, and 3 are all grounded and 4 is the +. Does that sound right to you? I assume on the new cap I could jumper the ground legs on the cap... but would need to make sure they aren't bridge some part of the circut. If they are then I need to bridge it on the circuit board or provide a leg to that point. Am I saying that right?

Regarding mounting the new cap... I'm thinking i'm going to try the insulated wire, heat shrink, and zip tie method. If I feel like it isn't sound enough then i will use the adapter board. If I use the adpater board I will buy some of the "Harwin (p/n H2101-01)". I assume those would only be needed if I used the adapter board?

Thanks again.

Addicted2AnalogTek · « **Reply #72 on:** April 03, 2018, 04:34:44 am »

Yes, as per your picture, 1, 2, and 3 are ground, 4 being the positive. When you install, just insert the ground wire from the capacitor into any of 1, 2, or 3. Assuming you choose 1, you'll want to use some wire to connect 1 to 2 and another wire from 2 to 3.

You are correct about the Harwin pins, you don't need those unless you're using an adapter board.

Have you formulated a game plan for removing that cap? Those things are tricky to get out without lifting the pads under the board.

DanielSpokane · « **Reply #73 on:** April 03, 2018, 04:41:57 am »

I was planning on just heating each connection point up and removing solder (using a sucker first and then desolder wick). After I get as much off as I can I was just going to heat and push, heat and push, etc. Think that will work?

When you say "... lifting the pads under the board" what of you mean by that? Do you mean watch out for traces lifting because of heat?... or physically removing the board(s)?

Addicted2AnalogTek · « **Reply #74 on:** April 03, 2018, 05:55:20 am »

What I meant by "lifting the pads under the board" is that when you apply mechanical force on the capacitor pins without them being free from the board, there's a chance the trace around the hole will be separated from the board.

I've been rather lucky when I've had to swap a cap and haven't had this happen, but I've seen a few posts where others have had that happen.

I don't have a vacuum desolering iron, so I use pretty much the same method you intend to use. I try to get enough solder removed from the large ground pin (pin 2 in your picture) and positive pin to be able to free them entirely from the board. Next, I grab the top of the capacitor, heat the solder on one of the remaining two pins and tilt the capacitor to pull the lead through just a little. Then I heat the other remaining pin and do the same, and switch back and forth until it's completely out. After the cap is out of the way, it's easy cleaning.

If you remove the trigger board, you might be able to get some side cutters in there and cut one of the pins off to make it a lot easier. It's not really necessary to remove the trigger board though. All a matter of preference.

DanielSpokane · « **Reply #75 on:** April 04, 2018, 03:02:23 am »

Got the cap out. Pictures are posted below. Went pretty easy... the only thing is one of the ground traces lifted just as Addicted2AnalogTek warned. You can see it in the last picture (looking down at the bottom next to the other PS filter caps). The trace goes to a ground screw that connects the side and bottom PCBs. I'm thinking I will glue the trace down with super glue (will have to drum up a curved stick or something to apply the glue to the underside of the trace). The only thing is... part of the hole tore off with the capacitor (you can see in the last picture )... thus it seems like there is a chance the ground connection isn't made when I solder the new cap in since I will be soldering from the bottom side opposite of the ripped hole trace. Hmmmm. I can test and make sure there is ground continuity... but worried it might be a weak connection. What do you think? Other than that... went well

Addicted2AnalogTek · « **Reply #76 on:** April 04, 2018, 03:36:56 am »

It looks to me like that ground trace may have burned up prior to your removal of the capacitor. Upon comparison with a spare board, it looks like that trace runs to the cathode of CR1569, the anode of CR1549, and then on to the ground TP/screw hole in front of Q1546. That's also where the notorious little 3uF 150V wet tantalum capacitor ( C1534 ) is grounded, but the ground trace between that area and CR1569 is a lot smaller, so I'd be expecting that to burn first if something in that area had failed. I'd check all of those components just to be safe. Others might have some ideas as to what caused that trace to burn - if that's what happened.

You may have to remove the trigger board for this, but one way to solve that problem is to gently scrape all the crud off of the board with a flat tip screwdriver, clean up with IPA, and then lightly scrape some of the good trace so you can solder some stranded wire down to it. Then just run the wire from the good trace and thru the hole. You could actually just use some used solder-wick instead of wire since it's a short run. Personally, I would feel that to be a more stable solution than trying to repair the damaged trace.

Good job on getting that sucker out, though! It's a monster compared to it's replacement!

DanielSpokane · « **Reply #77 on:** April 04, 2018, 04:02:50 am »

Thanks for the input. Yes I like the idea of running a wire on the trace. Maybe I solder it to the trace and through the hole then bridge the wire back to one of the other ground holes. Then run another wire from the other hole up to the new capacitor (and bridge the grounds on the cap). Seems like that would hold well and then I wouldn't have to worry about connecting the hole with the damaged trace directly to the capacitor. Seems like that might simplify the mechanical dexterity needed to do this.

Replacement capacitor is scheduled to arrive Friday!

DanielSpokane · « **Reply #78 on:** April 04, 2018, 04:03:42 am »

Also, I will check those other parts shortly to see if there is any sign of damage, etc. Thanks for the heads up.

DanielSpokane · « **Reply #79 on:** April 07, 2018, 11:44:44 pm »

Got the new capacitor in. Overall it wasn't too bad. I was able to re-glue the damaged trace; then used wire and solder for belt and suspenders just incase the trace was damaged or not fully intact. The new capacitor had two leads (instead of 4). Installed the 2 leads in existing holes then jumpered the other two open ground locations. Had to drill a couple holes in the ground trace to get everything to set... but worked well. After that... turned it on and works like a charm! Thanks guys! See pictures and video:

A couple things (which can be seen in the video):
1. When I move the trace for either channel up and down the screen there appears to be some visual distortion for a second that goes away. Any idea what is causing that?
2. Also, the intensity of the screen is really really bright. I have it at about 25% and that looks great. When I move it to 100% it gets insanely bright. Not a big deal... I guess I just want to make sure something else isn't out.

Overall a pretty sweet scope for $20 (at a thrift store) plus the price of a capacitor and a little elbow grease. Thanks again for all your help.

tautech · « **Reply #80 on:** April 08, 2018, 12:31:42 am »

Quote from: DanielSpokane on April 07, 2018, 11:44:44 pm

1. When I move the trace for either channel up and down the screen there appears to be some visual distortion for a second that goes away. Any idea what is causing that?
2. Also, the intensity of the screen is really really bright. I have it at about 25% and that looks great. When I move it to 100% it gets insanely bright. Not a big deal... I guess I just want to make sure something else isn't out.

All looks perfectly normal.

WRT CRO Intensity/brightness, you need good brightness when using delayed timebases and that's really the only time. Generally Service manual adjustment specifies that when set to Min the trace should just disappear and an additional bias pot is normally fitted on the PCB to get the brightness range correct.
It's a good idea to get into the habit of using only enough Intensity/brightness to see the trace clearly in order to preserve CRT life.

So now use it for a bit as your main scope, why ?.....well in order to get used to properly driving a scope instead of using Autoset. This is/isn't a dig so much as an experienced recommendation and it will help you later when using your DSO.

DanielSpokane · « **Reply #81 on:** April 08, 2018, 12:36:15 am »

Thanks for the info... and thanks for the recommendations regarding learning to drive a scope. Will do!! Looks like this is my new baby for a while!

Miti · « **Reply #82 on:** April 08, 2018, 12:58:30 am »

If you want my opinion, if this cap was dead, the others are most likely on their last legs as well. If I were you, i'd replace them too.

Quote from: DanielSpokane on April 07, 2018, 11:44:44 pm

2. Also, the intensity of the screen is really really bright. I have it at about 25% and that looks great. When I move it to 100% it gets insanely bright. Not a big deal... I guess I just want to make sure something else isn't out.

Apply 100MHz with X10 MAG, is it bright?

Addicted2AnalogTek · « **Reply #83 on:** April 08, 2018, 03:05:13 am »

Quote from: DanielSpokane on April 07, 2018, 11:44:44 pm

A couple things (which can be seen in the video):
1. When I move the trace for either channel up and down the screen there appears to be some visual distortion for a second that goes away. Any idea what is causing that?

This is typical of one of these scopes that's sat for a long period of time without use and should improve (for the most part) as you use the scope. It's being caused by some oxidation or buildup on the contacts inside of the vertical position pots. There's likely some other dirty contacts you'll discover soon enough, which also will likely improve with use.

Quote

Overall a pretty sweet scope for $20 (at a thrift store) plus the price of a capacitor and a little elbow grease. Thanks again for all your help.

Congratulations on your successful repair! That's one heck of a deal - $20 for the scope and maybe $10 for the capacitor after shipping, plus a little bit of time and effort!

Quote from: Miti on April 08, 2018, 12:58:30 am

If you want my opinion, if this cap was dead, the others are most likely on their last legs as well. If I were you, i'd replace them too.

I've found an easy way of discerning whether a supply cap is "on the fritz" from my time inside of a 468. The 468 manual has waveforms for the unregulated power supply rails which I haven't found in any other manuals. Upon probing the positive terminal of each cap with the same setup you would use for ripple measurements, you'll see if the cap is discharging smoothly or not. Now, if the ripple is in spec but the unregulated supply waveform doesn't look "clean", I'll just replace the cap. But of course, you need a second scope for that. Other than wholesale tantalum cap replacement (when they're obviously from the 70's-80's), I avoid wholesale parts replacement tasks. It just seems to be a waste of money when the OEM parts, if still good, may last at least several more years.

DanielSpokane · « **Reply #84 on:** April 08, 2018, 05:11:01 am »

Thanks again for all the help. I really appreciate it. You guys sure know your stuff!! This scope sure looks sweet on my bench now!

I will keep an eye on the other components and will replace when needed. I did buy another 5600uF cap just in case

Addicted2AnalogTek · « **Reply #85 on:** April 08, 2018, 07:50:20 am »

Quote from: Addicted2AnalogTek on April 08, 2018, 03:05:13 am

But of course, ~~you need a second scope for that.~~

I completely forgot that you can use the scope to check itself! I just double checked on a 465B. Just be careful probing! Make 100% sure that your ground lead DOES NOT TOUCH anything that is not a ground test point or the frame!!! In order to check the caps the way I described above, you just need to use a 1X probe and set bandwidth limit to 20Mhz. The settings you'll want to use are shown in the pictures I'm adding to the post.

>The first picture is the waveform you'll see when probing a good cap. This is what your new cap will look like.
>The second picture is the waveform of an acceptable cap (to me, anyway), but one I'd keep an eye on. If it were any worse, I'd just change it.
>The third picture is a bad cap, and one that I'll replace immediately. This bad cap is on the +15V rail, which measured less than 2mV ripple on the regulated output. It's still "acceptable" to the scope's power supply, but I wouldn't expect it to stay that way for long if I left it in.

If you decide to go ahead and check them out, I'd download the 468 service manual volume 2 from the TekWiki site and go to pages 169/171. You can then apply that info to your 465. If you haven't already, you should download or buy the manual for your scope and familiarize yourself with everything. Also download and read "Troubleshooting your oscilloscope: Getting down to basics" by Tektronix. It's a lifesaver! This way you'll be nearly ready when the time comes to tackle another repair.

EDIT The orientation of the photos has been changed when uploading and I'm not sure how to make them the proper orientation on here after they're attached.

tautech · « **Reply #86 on:** April 08, 2018, 07:53:50 am »

Quote from: Addicted2AnalogTek on April 08, 2018, 07:50:20 am

Quote from: Addicted2AnalogTek on April 08, 2018, 03:05:13 am
But of course, ~~you need a second scope for that.~~

See reply #34.

Addicted2AnalogTek · « **Reply #87 on:** April 08, 2018, 07:56:27 am »

Quote from: tautech on April 08, 2018, 07:53:50 am

Quote from: Addicted2AnalogTek on April 08, 2018, 07:50:20 am
Quote from: Addicted2AnalogTek on April 08, 2018, 03:05:13 am
But of course, ~~you need a second scope for that.~~
See reply #34.

Oh!! My mistake! I probably need sleep.. It's 4AM here.

tautech · « **Reply #88 on:** April 08, 2018, 08:06:30 am »

Quote from: Addicted2AnalogTek on April 08, 2018, 07:56:27 am

Quote from: tautech on April 08, 2018, 07:53:50 am
Quote from: Addicted2AnalogTek on April 08, 2018, 07:50:20 am
Quote from: Addicted2AnalogTek on April 08, 2018, 03:05:13 am
But of course, ~~you need a second scope for that.~~
See reply #34.

Oh!! My mistake! I probably need sleep.. It's 4AM here.

No matter buddy, you were a bit late to this party and probably missed the first few posts.

tautech · « **Reply #89 on:** April 08, 2018, 08:22:10 am »

Quote from: Addicted2AnalogTek on April 08, 2018, 07:50:20 am

EDIT The orientation of the photos has been changed when uploading and I'm not sure how to make them the proper orientation on here after they're attached.

Yeah my iPhone does that dumb trick too.
I import them into a pic viewer and flip them right side up, save and then post.

BTW, what phosphor is in your Tek ?
I do like those trace colors.

MarkL · « **Reply #90 on:** April 08, 2018, 02:25:55 pm »

Quote from: Addicted2AnalogTek on April 08, 2018, 03:05:13 am

Quote from: DanielSpokane on April 07, 2018, 11:44:44 pm
A couple things (which can be seen in the video):
1. When I move the trace for either channel up and down the screen there appears to be some visual distortion for a second that goes away. Any idea what is causing that?

This is typical of one of these scopes that's sat for a long period of time without use and should improve (for the most part) as you use the scope. It's being caused by some oxidation or buildup on the contacts inside of the vertical position pots.
...

You can also just operate the controls to their extremes 10 or 20 times or until the problem subsides enough to clear the wiper. But it's usually only a temporary fix and the jumpiness will be back.

bd139 · « **Reply #91 on:** April 08, 2018, 03:14:12 pm »

Sometimes that works. The vertical pots on mine are beyond that unfortunately.

Addicted2AnalogTek · « **Reply #92 on:** April 08, 2018, 05:33:27 pm »

Quote from: tautech on April 08, 2018, 08:22:10 am

Quote from: Addicted2AnalogTek on April 08, 2018, 07:50:20 am
EDIT The orientation of the photos has been changed when uploading and I'm not sure how to make them the proper orientation on here after they're attached.
Yeah my iPhone does that dumb trick too.
I import them into a pic viewer and flip them right side up, save and then post.

BTW, what phosphor is in your Tek ?
I do like those trace colors.

It's a 485 with option 4 (EMI filtering) and option 78 (P11 phosphor). It's got the CRT mesh filter, which makes the blue seem even more brilliant! It's great for pictures (as that's it's intended purpose), but I didn't realize just how unfriendly P11 phosphor is on the eyes. It plays tricks with my vision and drives my eyes out of focus if I'm looking at it for more than just a couple seconds.

Quote from: bd139 on April 08, 2018, 03:14:12 pm

Sometimes that works. The vertical pots on mine are beyond that unfortunately.

I've had success with "repairing" these pots. It's just time consuming is all. Here's a quick run-down of what I've done:

1- remove vertical board, desolder pots, disassemble them and remove the part of the pot that holds the wiper. I like to put the rest of it back together to maintain orientation, and so I don't lose anything....
2- soak the wiper assembly in 99% IPA for a bit (usually an hour or so). After the initial soak, grab one of the leads with pliers and "whip" it to fling out the IPA.
3- repeat #2 two or three more times
4- Blast out with compressed air - I use canned air so I don't have to worry about the moisture & oil that comes out of an unfiltered compressor.
5- Reassemble, install, and test.

I don't clean the lube out from around the shaft unless it's dirty. I did clean it out on an intensity pot assembly once and the dielectric grease that I used to replace it just didn't seem to allow smooth operation. It's not noticeable on the display, but when I went to adjust the grid bias and Z axis, the darn thing was so stiff that I had to fiddle with it for some minutes before I got it to the correct voltage. Maybe some contaminants remained behind before I re-lubed it, maybe I used the wrong stuff, or maybe I used too much - but now I just leave the original lube in there and only clean out the wiper assembly. Fortunately I've only had to do this 3 or 4 times, but it would seem I'm about to be doing it again with some of the "sealed" Allen Bradley type vertical position pots. I'd rather do that than dish out $30 for a pair of "new" ones or raid another scope for replacements, though!!

It's a lot easier to do if they're the A-B type with the four slotted screws holding it together. It can be performed on ones with the plastic pins as well, you just have to either glue or melt it back together afterwards. The Bourns pots with aluminum dowel pins I haven't attempted yet, but I'm confident those can be done as well - it could be as simple as finding some screws and nuts small enough to replace the aluminum dowels.

bd139 · « **Reply #93 on:** April 08, 2018, 05:53:00 pm »

Thanks for the tips. These are the old black AB ones with screws fortunately. Not sure I fancy taking the vertical amp to bits yet to get them out. Honestly I was hoping for another 465 to turn up as a parts mule so I have some backup pots first

Addicted2AnalogTek · « **Reply #94 on:** April 08, 2018, 06:14:08 pm »

IIRC, the 311-1311-00 pots are in all of the 400 series scopes except for the 468 and 485. The problem with using ones from a parts mule is that you're risking the chance of ending up with pots that are just as bad or worse than the ones you already have! I have a 465 parts scope with known good vertical position pots, and if I don't end up needing them for the 465B that's on the bench right now, I'd be willing to part with them. I'd understand if you'd rather hold out for a complete parts scope for all the extra replacements it contains!

bd139 · « **Reply #95 on:** April 08, 2018, 06:22:52 pm »

Plan was to test and refurbish the ones in the parts mule scope and then substitute them in. Path of least risk there. Annoyingly the entire scope is immaculate and looks like new (even feet are intact!) so I’m not sure why the pots are so scratchy. Probably why Bourns do the later model ones!

Thanks for the offer but alas I am waiting for a complete scope as I need some spares around. This is the first time I think I’ve had only one tek scope on hand and I’m never happy with that situation.

DanielSpokane · « **Reply #96 on:** April 10, 2018, 05:14:33 am »

You guys are a wealth of information!

Ok... here's a little less technical question.

Any idea where I can get 2 replacement cabinet feet (See picture). Mine has 2 but is missing the 2 rear feet. The screws are there for the missing feet... but the feet are gone. Almost looks like a kid or someone unscrewed the 2 right before I found it and bought it.

I searched for a bit on the internet but couldn't find anything in stock. I was thinking about making something....

tautech · « **Reply #97 on:** April 10, 2018, 05:20:49 am »

Quote from: DanielSpokane on April 10, 2018, 05:14:33 am

You guys are a wealth of information!

Ok... here's a little less technical question.

Any idea where I can get 2 replacement cabinet feet (See picture). Mine has 2 but is missing the 2 rear feet. The screws are there for the missing feet... but the feet are gone. Almost looks like a kid or someone unscrewed the 2 right before I found it and bought it. I searched for a bit on the internet but couldn't find anything in stock. I was thinking about making something....

Google for 'wall skirting door stop' and get one of the 'squat' (short) varieties.
They should really be non-conducting ......from the age when it was normal to float a scope.

Addicted2AnalogTek · « **Reply #98 on:** April 11, 2018, 05:15:09 pm »

Quote from: DanielSpokane on April 10, 2018, 05:14:33 am

Any idea where I can get 2 replacement cabinet feet (See picture). Mine has 2 but is missing the 2 rear feet. The screws are there for the missing feet... but the feet are gone. Almost looks like a kid or someone unscrewed the 2 right before I found it and bought it. I searched for a bit on the internet but couldn't find anything in stock. I was thinking about making something....

I'm about to send some out today to someone for reproduction, actually. If they are successful, replica replacements should be available in a couple weeks. They appear to be part number 348-0080-00 (according to the 485 manual). Until the reproductions are available, the only way I know of to score these is to take them from a spare case.

Be sure to put something over those studs to protect the threads until you have suitable replacement feet - if the threads get damaged, they'll probably need to be chased (cleaned with a die). It could be as simple as a wine bottle quark that you've cut to a decent height and then screwed onto the studs.

There's some similar ones listed on the evil auction site P/N 348-0187-00, but I have no idea if those ones have the correct threads to match up to the studs mounted to the 400 series scope cases. I don't think I'd want to pay $21.00 for two replacements that may not fit, though! It's great that your case still has the aluminum studs still attached - I have a 485 which had the two rear feet completely ripped off!

bd139 · « **Reply #99 on:** April 11, 2018, 05:31:57 pm »

Only about 20% of the scopes I’ve had over the years have had feet. First thing that buggers off usually!

Edit: when I sold my parts mule 465b ages ago I got the most money for the multiplier and feet (20 quid for the feet).

DanielSpokane · « **Reply #100 on:** April 12, 2018, 05:12:57 am »

Well I took a stab at making some feet. I used black hard rubber plugs and cut them down and drilled them out and installed a 6-32 nut. They aren't perfect but at a distance it's hard to tell the difference.

tautech · « **Reply #101 on:** April 12, 2018, 07:15:51 am »

Quote from: DanielSpokane on April 12, 2018, 05:12:57 am

Well I took a stab at making some feet. I used black hard rubber plugs and cut them down and drilled them out and installed a 6-32 nut. They aren't perfect but at a distance it's hard to tell the difference.

That's a good solution and they probably somewhat less delicate than the originals.

Where did you get them ? Chemical lab suppliers ?

DanielSpokane · « **Reply #102 on:** April 12, 2018, 06:59:54 pm »

I bought the hard rubber plugs at a local hardware store that sells lots of misc. stuff.

n0dyjeff · « **Reply #103 on:** May 20, 2018, 08:17:35 pm »

Quote from: DanielSpokane on April 10, 2018, 05:14:33 am

Any idea where I can get 2 replacement cabinet feet (See picture). Mine has 2 but is missing the 2 rear feet. The screws are there for the missing feet... but the feet are gone. Almost looks like a kid or someone unscrewed the 2 right before I found it and bought it. I searched for a bit on the internet but couldn't find anything in stock. I was thinking about making something....

I realize I'm coming late to the party, but I wanted to let the group know that I make and sell these bottom feet for the 465/465B/475/475A as well as the frequently broken rear cord wraps for the same scopes. I also sell feet for many other Tektronix instruments on my website https://www.n0dy.com. They're also available at a somewhat higher price on eBay. You can find them by searching on the Tektronix part number.

Jeff / N0DY

tautech · « **Reply #104 on:** May 20, 2018, 08:27:15 pm »

Welcome to the forum Jeff.

Nice selection of Tek feet and bumpers.

Another rear cable wrap foot that is commonly broken or missing are those for HP1740.
Will you branch out into supplying for other brands ?

n0dyjeff · « **Reply #105 on:** May 20, 2018, 08:44:49 pm »

Quote from: tautech on May 20, 2018, 08:27:15 pm

Another rear cable wrap foot that is commonly broken or missing are those for HP1740.
Will you branch out into supplying for other brands ?

Hi tautech,

I'm definitely interested in other brands, I just don't happen to have any of them lying around.

What I usually do for a part that is new to me find someone willing to lend me an intact existing part, plus do test fittings and take pictures of prototype units. In exchange, I send them their original part back plus a complete set of the final product at no charge.

If you think there's a need for the HP1740, I'd definitely like to develop a solution!

Jeff/N0DY

Slide_56 · « **Reply #106 on:** March 20, 2020, 02:26:16 am »

New member here.

Reviving this old thread, are the cap adapter boards still available somewhere? That thread appears to be gone and I'm not finding them at OSHpark.

Haven't yet begun to dig into the beast, but it's been sitting so long, cap replacement is inevitable.

Thanks.

Bill

med6753 · « **Reply #107 on:** March 20, 2020, 03:44:30 am »

Quote from: Slide_56 on March 20, 2020, 02:26:16 am

New member here.

Reviving this old thread, are the cap adapter boards still available somewhere? That thread appears to be gone and I'm not finding them at OSHpark.

Haven't yet begun to dig into the beast, but it's been sitting so long, cap replacement is inevitable.

Thanks.

Bill

https://www.ebay.com/itm/Capacitor-Adapter-15-5mm-triangle-recapping-vintage-equipment-Tek-465-kit-x5/273254508468?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

oventech · « **Reply #108 on:** March 27, 2020, 01:56:56 am »

Great thread. Have 2 475's to check out. Like that info on the PS waveforms. Will do. Thanks.

WattsThat · « **Reply #109 on:** March 27, 2020, 03:17:10 am »

The eBay boards certainly appear to be nice, universal design.

If you want to go the diy path, you can download the Gerber’s for the original pc boards in this thread:

https://www.eevblog.com/forum/repair/making-dave_k_s-capacitor-adapters-at-osh-park/msg1218875/#msg1218875

Scroll down in the thread to the Version 2 version boards as the drill holes don’t show up in V1. Just download the zip and point the OSH Park tool to the zip file and it’s off to the races. The small was $6.15/3 the large $8.05/3.

jxjbsd · « **Reply #110 on:** March 27, 2020, 09:25:16 am »

I like the old Tek CRT oscilloscope。A few days ago, a 465 was repaired. Its brightness was out of control 。And an injured 468


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