Author Topic: Tektronix 2465B oscilloscope teardown  (Read 440318 times)

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Offline med6753

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1175 on: October 01, 2018, 07:40:43 am »
med6753, gorgeous machine  :clap: and thanks for sharing the nicely shot detail photos.  :-+

Thanks for the flowers  :-+

Is there any reason you don't use the forum's attachment instead of hosting them at imageshack ?

Personal preference I guess.

Really worry if someday imageshack acting up, all of this great photos with details will be lost, as we already have few valuable post that had photos gone at earlier posts in this thread alone.  :'(

Yes, it's a risk. I was a victim of the Photobucket asshattery but I did go back and fix all my pictures, including in this thread. I think the other image services such as Imageshack took note of what happen to Photobucket and I'm hoping they learned from it. And I also to pay a nominal fee to Imageshack so I think we're safe.   
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Offline kcbrown

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1176 on: October 01, 2018, 08:02:37 pm »
What were my results? The fan motor for the first time since I've owned this scope is totally silent. So far the repair has worked and I've run it several hours. Will it last? Hard to say. I think this motor is potentially on it's last legs. But so far it's a thumbs up.  :-+

Totally silent because it's not turning at all?   ;D

Sorry, just had to ask.   >:D

 

Offline mnementh

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1177 on: October 02, 2018, 01:28:58 am »
Awesome pictorial med... good detail and the angles are actually useful.  :-+

My recommendation is specifically synthetic motor oil; I used 0W-30 or 5W-30 in the motor on my 2230 a decade ago and still quiet.

The collet-clamp on the fan in these are a total pud to get off without them cracking just like yours. My experience is that this is a losing battle... even ones I know I got free without breaking a few years ago were discovered broken in-use later. I tried the CA thing; it just broke again on one side or the other of the glue joint.  :palm:

IIRC, the fan on my 2230 (or maybe it was one of my 2465s) is just held on by friction; I discovered after using it for a couple years that it had been that way all along; there was no threaded shaft/nut at all.

When I reassembled, I just put the the cone portion onto the shaft and pressed the fan in place with moderate force while holding the can of the motor inside the 'scope. I tried pulling it off and it was on there much tighter than the press-fit most such fans are equipped with; and so far, it has not worked loose YET after many years. Lets just call it an ongoing experiment; whichever scope it's still on. ;)

   I keep telling myself I'm going to find one of these that fits the taper of the fan; but alas, so far I couldn't be arsed to carry through with that plan.  :palm:

I'll post my detail of actually servicing the motor itself here in retaliation... not gonna let you get off scott-free. ;)

mnem
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Offline mnementh

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1178 on: October 02, 2018, 01:50:43 am »
2465 Blower Motor Service

We've all seen a number of articles on rebuilding the 24xx SMPS, and as those who own a 2465 (or any of several other models of this vintage) know, the Seimens canister brushless motor in them can be a bit of a hairball to service when it dries out and starts to squeal/chirp.

Many of us are aware of this article outlining the COMPLETE "Refurbishment" of one such motor that had knackered bushings, but for many of us (hopefully MOST who are still into these old beasts) the damage is not nearly so bad, and none of us want to volunteer for THAT level of dismantling.  :scared:

Here is the process I've arrived at over the years for servicing the actual motor; as always YMMV, DQMOT, WTFBBQ? DILLIGAF?!? (take your pick) applies...

DISASSEMBLY:




I start out with desoldering the driver PCB because I've seen enough other disassembly tutorials on the SMPS itself; including a good one by med6753 just a few posts above this one.  I don't feel a need to recurse those articles yet again.




Before we start disassembling, take note of the endplay on the motor shaft. If your motor is mostly healthy, it'll be pretty small. Your fingers are a pretty good judge of what is reasonable, but if you feel a need to mic it out, look for 0.5-0.8mm. If it's really loose then you have other problems, like med there who found a big open hole in the back of his motor.  :o




This is what you SHOULD find on your endbell; a little hole sealed up with the ubiquitous Silastic cement. If it's not all dark brown & hard, your motor probably didn't get run dry for too long.  :-+




The Silastic will pick out easily in most cases...




But watch out; those German engineers left a booby-trap in there for ya that COULD kill your motor if you're careless. So don't be. ;)




Once you have the pooky all picked outta the hole, the set screw comes out with very little force. It's not a proper threaded hole; more like the kind where the screw cuts its own threads into ridges molded into the hole like those old fashioned tuning coils from the dawn of electronics. The great wheel never stops turning. ;)

There's really only a few grams of thrust force here as long as you aren't abusing the thing; it doesn't really need much thread to hold. This is what a healthy set screw/thrust bearing looks like; a mirror smooth surface. I wouldn't worry about a little dimple in the surface either; but if it has been run dry a long time, that screw could be chowdered up pretty bad.




This is where the crunk hits the air circulation device; cleaning the dried out oil remains so the bushings can... bush... again. I've seen some that were really bad; it looked like it had caught fire in there. Another that actually had some form of bacteria growing in/on the plastic body.  :scared:

Use your preferred plastic-safe degunker here; I prefer CRC # 03040 Food Safe Industrial Silicone Spray Lube. It tastes like it has an alcohol carrier and the SMDS lists some stuff ending in ane, so probably some kind of plastic that it's not safe on... however I've been using the stuff as contact & control cleaner (especially nice on pots & faders) for over a decade and haven't found it yet.

From the Q&A on the product page above:

Quote from: Amazon Q & A
Four items totaled are listed on the can. (1) Hydrotreated light naphtha is a light petroleum. (2) 1,1Difuorethane is a propellant listed as safe to use by the EPA for food. (3) Polydmethylsiloxane is a type of silicone. (4) n-Hexane 110-54-3 is a crude oil product that evaporates very quickly into the air and is used to extract vegetable oils from crops like soybeans. I use this product on my Cabela's meatgrinder after I've cleaned it, dried it, and before I put it away. It keeps away the rust while keeping the product lubricated between uses. Also never use this product near an open flame as it is very flammable.

So anything naphta will dissolve might be a problem... not sure. I'm sure Cerebus will be along any minute now to correct me. ;)

Bottom line is it dries quickly, leaving only a thin silicone lubricant film behind.







Chuck up the shaft gently; just barely tight with your fingertips. Hold the motor can lightly and run the drill on high speed to work your degunker through the bushings. Spray, run drill, spray again until the backwash runs clear and it looks clean inside the bushing holes.

Play it safe; put the motor somewhere with good ventilation, preferably warm, and let it dry overnight.



You wanna wipe the outside of the motor can down with alcohol before you put her to bed for the night; that silly-cone spray does make holding her a wee bit like handling an eel.

And finally... I'm gonna end this segment with...




Yes, they are relevant. I promise.

Cheers,

mnem
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« Last Edit: May 02, 2019, 12:49:51 pm by mnementh »
 
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Offline mnementh

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1179 on: October 02, 2018, 01:55:31 am »
Thrust Bearing Service:



Once you've cleaned the motor, the next step is to service the thrust bearing. If your set screw/thrust bearing is chowdered up from being run dry, you'll need to find a way to get a smooth flat or domed surface for the motor shaft to ride against.

This is offered as an alternate repair method to that in the article on antiqueradios.com I linked to earlier;  I don't know many people who would want to take on building a jig and hand-lapping a thrust bearing surface that way.  :palm:

The ball needs to be close to the exact size of the hole to prevent chattering; this will still leave 3-4 turns of thread for the set screw behind the ball. If the hole in your motor isn't tight enough to install the set screw on top of a ~3mm ball, you can omit the set screw altogether and fill the hole with epoxy, or you may want to touch up the thrust surface on the set screw instead.

If your set screw/thrust bearing is in good condition, ignore this step and move on to oiling/reassembly.





Another tactic for repairing a chowdered surface is to chuck the set screw up in a drill (use moderate force or you'll damage the threads) and dress the end against the flat of a fine stone or cut-off wheel on a Dremel with the drill running at the same time as seen here. This is a poor man's "precision ground surface".  >:D

I use this tactic quite often to repair the ends of "special screws" that have been started crooked and damaged the threads on the end. A little chamfer once the bad threads are ground away and that screw is saved.  :-+



This is what this screw looks like right after being ground on the flat of the cut-off wheel; I wouldn't be afraid to use this as-is, quite honestly. Took a couple minutes including setting up drill and Dremel. If followed by dragging across 600-800 grit emery cloth with the drill running, it is surprisingly quick and effective.



This is what it looks like after running it in the drill with a few quick passes on one of my wife's discarded fingernail buffing blocks. These are NOT emery boards (which my wife steals from me all the time... grrr...  :rant: ) but final polishing abrasives on a dense foam brick. As you can see here, moderate pressure when chucking up in the drill resulted in no damage to the threads.

It actually took me longer to get three decent pics than it did to refinish the end of this m3 set screw from my parts bin.    ;)

Again; if your set screw/thrust bearing is in good condition, ignore these steps and move on to oiling/reassembly.




OILING AND REASSEMBLY:

My preferred lubricant for small motors is full synthetic 0W-30 or 5W-30 motor oil recovered by allowing "empty" oil bottles from an oil change in my car to drain into an old pill bottle like this one overnight.

I use a ~ 2mm wide blade-tip screwdriver as a precision applicator; dip it in the bottle then quickly apply 2-3 drops right on the shaft and let it sit for several minutes in an upright position before doing the same on the opposite end. Repeat for both ends, and repeat again if it appears to just suck the oil in. There is felt batting around the bushings; you are trying to re-saturate it with fresh oil.

This is a brushless motor; the worst that can happen is some oil mess. Of course, use some common sense... a big puddle of oil in your 24xx later could become a big hassle.  ::)

Let the motor sit overnight after oiling if you can; this will give the oil plenty of time to soak into the batting, and you'll be reasonably sure it's not gonna drip after you reinstall it.



Reinstall the set screw/thrust bearing. Just turn it in a few turns; don't tighten it.



Sorry for the fuzzy pic; it was the best one of several and the motor's all back together now.

Adjust endplay so it feels the same as when you first disassembled the motor. Your fingers are a pretty good judge of what's reasonable endplay. If you feel a need to mic it out, or if your set screw was chowdered up or missing obviously this will be way off; look for 0.5-0.8mm.  :-+




Use your sealant of choice to close up the hole and lock the set-screw in place. I prefer silicone RTV sealant as it is eazy to remove if needed.

DON'T FORGET THE PLASTIC SPACER when you reassemble the motor to the driver PCB.




TESTING:

A healthy motor will start at around 8V with a 30mA draw; set your power supply with current limited accordingly for initial test. The shaft is hard as hell and mirror-finished; a mark with a Sharpie will make it a lot easier to see when it starts turning. Let it run a few minutes, checking resistors and driver IC to be sure they get no more than warm.




Here we're going to put the fan on temporarily for performance tests. Just press it onto the collet cone; it will hold. No sense to risk breaking it by tightening the nut.




Here we're running at 12V; it's drawing approx 60mA. Fan is running just above idle. Note location of thermistor and pinout of 0.100" power header.

Dont forget to test/replace that electrolytic cap seen on the upper right corner by the motor. It is prehistoric too. ;)




Idling at 8V; drawing ~40mA.




Idling at 12V; drawing ~55mA




And here's the last step; testing the thermal speed control.  Place your soldering iron CLOSE to the thermistor, but don't make contact. The fan motor should start to ramp up speed in a few seconds. You'll need to up the current limit on your power supply if you haven't already.

Do several cycles of "apply heat, fan speeds up / remove heat, fan slows down" and observe the motor; it should still be pretty much dead silent at these low voltages. IIRC, it runs on 18-20V in situ.  Remember to keep checking resistors and driver IC for overheating while testing.

If it runs cool and quiet, time to put it back in... unless you haven't let it sit overnight since oiling it.

You REALLY should take the time, just to be sure of no oily puddles.  :-+

Cheers,

mnem
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« Last Edit: October 02, 2018, 05:03:51 pm by mnementh »
 
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Offline med6753

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1180 on: October 02, 2018, 03:10:05 am »
Mnem...great write up!  :-+ If my motor takes a dump again I may try this procedure. Or just scrap it and install a computer fan. I already have one built up and modeled and ready to install if required.

I also used synthetic motor oil.....5W-30 to be exact.

Yes Kcbrown, the fan is running.  :-DD
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Offline AMR Labs

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1181 on: October 09, 2018, 07:24:38 pm »
Finally bit the bullet and took the plunge on a 2465B SN 55xxx with what seems good front panel cosmetics on the advertised pictures, including the storage pouch and... A FRONT COVER (!), AC cable but sadly no probes. All for less than $200 plus a bit of S/H. Seller was in same state so shipping went dramatically down, and that certainly gave me some extra legroom towards my willingness on how far to go on the final purchase price given the "As-Is" clause and reported condition (see bellow).

Now for the finer details... sounds to me this scope has the typical symptoms of bad DAC ref voltage due to leaking cap corrosion problem on the A5 board (I hope that's all it is!!). Seller said the scope shows a TEST 05 FAIL 40 upon power up, and that subsequently the traces show quite a bit of jitter and after a while they wander off-screen towards the bottom. Well I guess at least there are live traces present, one fewer problem to deal with, and hopefully the cal constants are still intact.

But in spite of this somewhat risky sounding error and obvious less than ideal condition, after weeks of reading so many very detailed descriptions on how other people, many with little or almost no previous knowledge on these great scopes (just like myself), managed to successfully pull trough their restoration projects. So I decided that it was time and also felt ready to take my chances. This thread alone speaks volumes about how reassuring it is to be in good company when it comes to so many like-minded 246x scope enthusiasts out there, and the great pool of resources that has been built up so far because of so many people posted their detailed experiences. I probably expect to have more questions than answers, but in the end hope to be able to contribute a tiny bit as well towards adding more useful information to this thread for the next newcomer.

So now I'm off to start working on the parts purchase list. Guess I start focusing first on the A5 restoration, and then move on to recap the power supplies as needed. I have seen numerous references to capacitor lists with Mouser (and/or Digikey?) part numbers.

I've attached a picture of the new acquisition, hope to get it in about 2 weeks or so.
More pictures of teardown to follow.

Any comments and suggestions will of course be very welcomed.

PS. Does anybody know what Option 46 is? Can't remember off hand, and its not on my Options short list I had hand compiled, nor is it mentioned in the service manual (section 7.1)
Picture attached of rear panel as well.
« Last Edit: October 09, 2018, 08:41:02 pm by AMR Labs »
 

Offline MarkL

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1182 on: October 19, 2018, 01:48:49 am »
I said...

...
It also seems like the 2465A only has entries from 0-254. 255 is zero and from 256 onwards the values wrap around. Is that enough to back up all of my calibration data?

I don't feel like experimenting with restoring the settings, but I'm happy to write another script that does this over GPIB in one go if someone is willing to test.
...
The 256 values should match what you see in EXER 02, in which case, yes, it has all of your calibration data.

Putting the calibration data back via GPIB works on a 2465(plain), but I haven't heard of anyone trying it yet on an A or B.  There's no reason to think it would operate differently, but until someone tries it I guess we don't know for sure.  I've been watching for an A or B junker on ebay for some time now to do this experiment.

Nice find on the "f" option to the EAROM command, thanks!

I finally got a junker to try this on.  $70 on ebay for a 2445A with DVM option, CTT, and GPIB.  I bought it for parts, but the only thing wrong with it was a bad INTENSITY pot.  No fun at all.

So the answer is "yes".  If you push the values displayed via EXER 02 back via GPIB, it works.  You'll need to convert from the hex on EXER 02 to decimal for the GPIB commands.

To repopulate the NVRAM contents you can also directly replay the output of the GPIB NVRAM read data, providing an easy backup method.

This should also work fine on the "B" series since the NVRAM operation is essentially the same.

If you've completely lost your NVRAM, the scope will come up with random and bizarre settings.  Put the NVRAM contents back via GPIB and then power cycle it.  The settings will still be random because the GPIB writes only put back the calibration data (and not the settings).  I couldn't find a "factory default" setting, but if you exercise all the controls to make the settings sane again, all will be ok.

For reference, here's the post that describes the GPIB commands:

  https://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/msg1167050/#msg1167050

If anyone wants it, attached are the NVRAM contents from the 2445A from both the EXER 02 and the GPIB interface.  They are the same.  Obviously this cal data is specific to this scope.
 

Online 0culus

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1183 on: October 19, 2018, 03:22:51 am »
I recently got my Tek 2465B and love it. Amazing piece of kit. I ended up finding a pretty good deal on a freshly refurbished and calibrated one (also got a P6137 10x probe and a P6101 1x with it) just the basics as far as options go. This thread helped me decide to pull the trigger because I feel confident that I too can learn how to work on this scope down the road.

Since I recently acquired an RF signal generator (HP 8657A) that goes to 1040 MHz, I wanted to test out the upper limits of bandwidth on the 2465B. I was able to acquire an accurate frequency measure with the cursors at 800 MHz, +130 dBf. Obviously it is heavily attenuated and a bit noisy. Probably not useful in practice, but you can't touch any modern digital scopes with that bandwidth for less than $1000 US. 
 

Offline tggzzz

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1184 on: October 19, 2018, 08:29:19 am »
I've had my Tek 485 display a stable >1GHz signal. Not bad for a 350MHz scope :)

The limitation wasn't the frequency, but the amplitude of the signal; the limit was set when the amplitude fell to <0.2 divisions. That is a good illustration of the quality of Tek's tunnel diode trigger circuits.
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Offline BravoV

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1185 on: October 19, 2018, 08:40:35 am »
I've had my Tek 485 display a stable >1GHz signal. Not bad for a 350MHz scope :)

The limitation wasn't the frequency, but the amplitude of the signal; the limit was set when the amplitude fell to <0.2 divisions. That is a good illustration of the quality of Tek's tunnel diode trigger circuits.

When it comes detective works, especially on hunting down spurious high freq > 400 MHz oscillation, combined with my 2465B 400MHz limitation just to see the signal, then I used 3GHz spectrum analyzer + 2.5 GHz RF probe to catch them for the amplitudes and span, a resource limited hobbyist grade HF probing technique.  :P

Online 0culus

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1186 on: October 19, 2018, 09:12:44 pm »
I've had my Tek 485 display a stable >1GHz signal. Not bad for a 350MHz scope :)

The limitation wasn't the frequency, but the amplitude of the signal; the limit was set when the amplitude fell to <0.2 divisions. That is a good illustration of the quality of Tek's tunnel diode trigger circuits.

Wow! What probes did you use for that?
 

Offline AMR Labs

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1187 on: October 26, 2018, 03:35:11 am »
Scope arrived, finally.

This is a 2465B SN 55K off ebay, very good cosmetics, and insides are very clean, almost no dust anywhere. Has a TEK U800, and NVRAM has a date code 9020. Most chips are also 1990's. I attached some general pictures. More detailed pictures to follow.

Plugged in, power on, but no trace or readout on screen. Self test stops at the "ADD" label, which means a Test 05 Error of some kind. Seller's description stated that the scope was showing an Error 05 Fail 40, which means "Positive Level too positive", and I assumed most probably due to corrosion on the A5 board due to well known leaky caps, which now is already confirmed ->detailed pictures of clean-up to follow as well. Seller also stated that trace had a lot of vertical jitter, and after a while it would move off screen towards the bottom. Not sure how long ago this scope still had a visible trace upon power up.

Anybody has any ideas/suggestions on why there is no trace?

Oh, and yes, I will definitively check all the voltages at J119 once I get the mess cleaned up on A5.
« Last Edit: October 26, 2018, 03:37:33 am by AMR Labs »
 

Offline AMR Labs

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1188 on: October 26, 2018, 03:55:23 am »
Decided to keep on going tonight with the leaky caps removal and pad clean-up, so here are some pictures of the process. I followed the recommendation of a very knowledgeable member of the Tek Scopes group to not attempt to lift the caps in one piece, as it is very easy to damage or lift the pads off the board, but rather to chop them up to pieces and get down to the pads before trying to desolder what was left. Also, while desoldering not to pull up, but rather to slide to the side any remains of the caps connecting leads. Well I actually desoldered the single cap on the other corner in a conventional way and all went well, but decided against it where the other 3 caps are very close together.

The pads of the caps cleaned up quite well, not much damage due to corrosion or any eaten away traces that I could spot. But as one can see there is a wide area of other affected parts that will need to be cleaned (affected IC legs), or replaced in the case of caps and resistors. Once all those other affected SMD parts have been removed, the other recommendation is to wash the affected areas with water, dish soap and a soft toothbrush to get rid as much of possible of any remaining electrolyte left over from the leaking caps. Then put the board into a convection oven to dry.

Here are some before and after pictures of the repair in the area of the 3 caps.
 

Offline AMR Labs

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1189 on: October 26, 2018, 04:02:26 am »
Here is the other affected area on the A5 board where the remaining single leaky cap was located. Quite a bit to clean up and replace as well around that area. Apologies for the almost duplicate pictures, but I couldn't quite get the right camera angle that would show all the places with greenish or dull spots.

Comments and suggestions welcomed.
« Last Edit: October 26, 2018, 04:05:35 am by AMR Labs »
 

Offline BravoV

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1190 on: October 26, 2018, 04:28:46 am »
AMR Labs, congrats on the score !  :clap:

Also thanks for sharing the photos, really appreciate it.  :-+

About the leaky caps, suggesting to check if the surrounding thin traces for continuity as it seems like they're corroded too, also reflowing the solder at the surrounding components as their solder joints look tarnished, not shiny as neighboring solder that are far away from the leaky caps.

Put few example highlighted points by arrows on the affected traces.
« Last Edit: October 26, 2018, 04:33:26 am by BravoV »
 
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Offline tggzzz

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1191 on: October 26, 2018, 08:33:21 am »
I've had my Tek 485 display a stable >1GHz signal. Not bad for a 350MHz scope :)

The limitation wasn't the frequency, but the amplitude of the signal; the limit was set when the amplitude fell to <0.2 divisions. That is a good illustration of the quality of Tek's tunnel diode trigger circuits.

Wow! What probes did you use for that?

None! BNC coax, 50ohm termination in the scope. 

The 485 has two attenuators, one 50ohm and one 1Mohm. None of this "stuff a 50ohm resistor across the 1Mohm//20pF input and call it 50ohm" crap :)
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Offline grbk

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1192 on: October 26, 2018, 02:22:08 pm »
Plugged in, power on, but no trace or readout on screen. Self test stops at the "ADD" label, which means a Test 05 Error of some kind. Seller's description stated that the scope was showing an Error 05 Fail 40, which means "Positive Level too positive", and I assumed most probably due to corrosion on the A5 board due to well known leaky caps, which now is already confirmed ->detailed pictures of clean-up to follow as well. Seller also stated that trace had a lot of vertical jitter, and after a while it would move off screen towards the bottom. Not sure how long ago this scope still had a visible trace upon power up.

Anybody has any ideas/suggestions on why there is no trace?

Oh, and yes, I will definitively check all the voltages at J119 once I get the mess cleaned up on A5.

Your scope sounds almost exactly like mine. The problem is almost certainly just the DAC circuit on A5 due to the capacitor corrosion. That DAC circuit is used for controlling pretty much everything in the scope. ADD being illuminated also suggests you have a DAC problem. Fix A5 and you'll be good to go.

I say this from experience -- a couple weeks ago I purchased a SN005xxxx 2465B, datecodes ~1990, with no trace (advertised as "HV collapses") for not much money. Finished fixing it the other day (have not recapped the power supply or replaced the NVRAM yet; those are next on the list). I haven't yet gotten around to writing it up for this thread and posting my pictures, but here's the abridged version for you & posterity.

My issues checked out almost identically to yours. No trace. Startup checks left ADD illuminated, indicating some kind of Test 05 failure.

I could turn grid bias up all the way and at least get a readout, but no visible trace; at least now I could see that the error was Test 05 Fail 44. I checked the reference voltages generated by the A5 DAC. From memory, I think they're supposed to be +1.36V and -1.25V, but they were way low. You can also probe these at some of the front panel pots (e.g. intensity). I also ran the front panel control exerciser routine (EXER01) which showed limited range for many of the front panel controls, again due to the missing reference voltages (they're used as the positive and negative supplies for many? of the front panel pots).

I replaced all of the SMT caps and a good chunk of the DAC circuit resistors on A5. My procedure was roughly this:
  • Identify parts to be replaced. I did R2011, R2012/R2013, R2014, R2015, R2016, R2413, and R2885. These were unscientifically singled out because they were physically close to the SMT caps and appeared to have some corrosion on or around them. Also suspect is the DAC itself, U2101, as well as the adjustment pot R2010. U2101 and R2010 looked okay to me, and R2010 measured fine, so I did not replace them. I didn't bother figuring out which ones were actually causing me problems, just replaced them all. Most of them measured okay out of circuit. The precision 10K 0.1% R2012/R2013 are probably most critical, and the consensus seems to be that those are most easily damaged by the corrosive electrolyte.
  • pre-clean the board to make desoldering easier. I used hot water with dish soap and a brush, then rinsed with distilled water. Dry in the oven on the lowest heat setting for a few hours. Apparently IPA does not effectively clean the electrolyte. I've also seen recommendations to use ammonia or another base to neutralize the acidic electrolyte, but I didn't do this. I focused on the areas around the SMT caps, particularly the DAC resistor network and the DAC itself.
  • scrape solder joints on those parts with an x-acto knife to remove corrosion and reveal as much fresh solder as possible
  • desolder components identified earlier. I used hot air and liberal amounts of flux. Carefully slide the components sideways off the pads after the solder liquifies (do not apply any force before the solder is melted) to avoid damaging pads. I managed to keep all my pads & traces intact, so I guess the electrolyte damage to the board was minimal and only affected the resistor networks. When in doubt, buzz out the board to make sure everything's intact.
  • Clean flux with your preferred flux cleaner. I used IPA
  • Clean electrolyte. See 2. You're trying to remove anything that was hiding underneath the components you removed. Bake again when you're done.
  • Solder in your replacement components. Probably easier to do resistors first and then capacitors, especially if your replacement caps are also electrolytics, since they kind of block access to the resistors.
     You could probably do this with solder paste and hot air, but I just used my iron and regular solder. 1206 resistors make that no sweat. Buzz it out to make sure everything is a-okay.
  • Clean flux again and reassemble  :-+

If you turned up grid bias during the debugging phase, you'll probably want to turn it down again before powering up. You'll also want to run through the CRT adjustment procedure if you tweaked grid bias. It's pretty easy and does not affect your other calibration steps.



 
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Offline AMR Labs

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1193 on: October 27, 2018, 04:18:54 am »
@BravoV

Thank very much for the pointers. Yes next step I plan to undertake an extensive cleaning effort of the affected areas to remove any traces of capacitor electrolyte left on the board and in between components, and of course replace well known suspect parts. I am planning on putting together a purchase list of all the parts in the DAC area, including the reference resistors, capacitors, as well as the adjustment trimmer which frequently also seems to go bad in these cases. I wonder if anyone out there has the Mouser PNs of these parts? That would make it so much easier to order them.

Should be posting more pictures as I make progress, hopefully soon. This forum thread has already become a must read reference for any 2465 enthusiast, so I think the more information is added the better it will be getting over time to help others that follow. It certainly got me started. Thanks again for the arrows!
 

Offline AMR Labs

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1194 on: October 27, 2018, 04:55:55 am »
Plugged in, power on, but no trace or readout on screen. Self test stops at the "ADD" label, which means a Test 05 Error of some kind. Seller's description stated that the scope was showing an Error 05 Fail 40, which means "Positive Level too positive", and I assumed most probably due to corrosion on the A5 board due to well known leaky caps, which now is already confirmed ->detailed pictures of clean-up to follow as well. Seller also stated that trace had a lot of vertical jitter, and after a while it would move off screen towards the bottom. Not sure how long ago this scope still had a visible trace upon power up.

Anybody has any ideas/suggestions on why there is no trace?

Oh, and yes, I will definitively check all the voltages at J119 once I get the mess cleaned up on A5.

Your scope sounds almost exactly like mine. The problem is almost certainly just the DAC circuit on A5 due to the capacitor corrosion. That DAC circuit is used for controlling pretty much everything in the scope. ADD being illuminated also suggests you have a DAC problem. Fix A5 and you'll be good to go.

I say this from experience -- a couple weeks ago I purchased a SN005xxxx 2465B, datecodes ~1990, with no trace (advertised as "HV collapses") for not much money. Finished fixing it the other day (have not recapped the power supply or replaced the NVRAM yet; those are next on the list). I haven't yet gotten around to writing it up for this thread and posting my pictures, but here's the abridged version for you & posterity.

Excellent write up grbk, thank very much for the information. Your case being so similar really encourages me to think I will be solving the display problems with an A5 repair as well.

Quick question: what would you say are the easiest access points to check on the +1.36V and -1.25V DAC reference voltages? Wanted to do a quick "1-2-3" check on that to see at what level those voltages are actually now, before and after the board wash of the two separate affected areas. And eventually after the required parts are replaced. Kind off to keep track of those voltages, mostly out of curiosity. Are there any easy access test points on the A5 board itself, or maybe some pins on one of the on board connectors? I do have the service manual but have been kind of overwhelmed a bit between some lack of time and all the huge amount of technical information in there, so at times one tends to loose track of what is where. Guess it will get better after I have gone through it enough times to familiarize myself with the content on a greater extent.

BTW by any chance do you (or anyone else out here) would have handy an already made list of specific Mouser PNs of the usual parts that need to be replaced in the DAC area? I've come across a list with Digikey PNs for some of the caps and resistors, which is a start but would also like to order the DAC trimmer resistor as well, just in case. And for several reasons, including the above and beyond easy and friendly quality user experience, my preferred go to parts place for years now has always been Mouser.

Thanks again for the great write up. I will send in some more updates of progress on the board wash hopefully in the next couple of days, as time and other occupations pressing for attention as well do permit.
« Last Edit: October 27, 2018, 05:08:02 am by AMR Labs »
 

Online 0culus

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1195 on: October 27, 2018, 04:58:44 am »
I've had my Tek 485 display a stable >1GHz signal. Not bad for a 350MHz scope :)

The limitation wasn't the frequency, but the amplitude of the signal; the limit was set when the amplitude fell to <0.2 divisions. That is a good illustration of the quality of Tek's tunnel diode trigger circuits.

Wow! What probes did you use for that?

None! BNC coax, 50ohm termination in the scope. 

The 485 has two attenuators, one 50ohm and one 1Mohm. None of this "stuff a 50ohm resistor across the 1Mohm//20pF input and call it 50ohm" crap :)

D'oh, of course!
 

Offline grbk

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1196 on: October 27, 2018, 06:09:32 am »
Quick question: what would you say are the easiest access points to check on the +1.36V and -1.25V DAC reference voltages? Wanted to do a quick "1-2-3" check on that to see at what level those voltages are actually now, before and after the board wash of the two separate affected areas. And eventually after the required parts are replaced. Kind off to keep track of those voltages, mostly out of curiosity. Are there any easy access test points on the A5 board itself, or maybe some pins on one of the on board connectors? I do have the service manual but have been kind of overwhelmed a bit between some lack of time and all the huge amount of technical information in there, so at times one tends to loose track of what is where. Guess it will get better after I have gone through it enough times to familiarize myself with the content on a greater extent.

BTW by any chance do you (or anyone else out here) would have handy an already made list of specific Mouser PNs of the usual parts that need to be replaced in the DAC area? I've come across a list with Digikey PNs for some of the caps and resistors, which is a start but would also like to order the DAC trimmer resistor as well, just in case. And for several reasons, including the above and beyond easy and friendly quality user experience, my preferred go to parts place for years now has always been Mouser.

Thanks again for the great write up. I will send in some more updates of progress on the board wash hopefully in the next couple of days, as time and other occupations pressing for attention as well do permit.
I’m out of town for the weekend so unfortunately I can’t provide specifics or take a picture of the schematic where I circled my test points for the reference voltage. However they should be straightforward to find if you compare the schematic and layout view. On the SMT A5 board, there are no explicit test points for the reference voltage, but they are easy to access on component terminals, I just don’t remember which components. First find the reference voltages in the analog control schematic (they’re labeled clearly), then identify which components have those voltages on them (for each there should be an op amp and probably an analog mux and maybe a capacitor). Then identify the components on the layout diagram. The voltages are also available on some of the front panel pots — intensity for sure, don’t remember which others. The schematic is clear on this though. They are undoubtedly on some headers/cable assemblies as well but I don’t know which and I didn’t investigate carefully.

As far as I can tell the original R2010 trimmer is no longer made. However it looks like a standard 20K cermet trimmer so I ordered Bourns PN PVG3A203C01R00 which should have the same footprint and otherwise be equivalent. However I didn’t end up installing it since the original one measured ok, so your mileage may vary.
 

Offline AMR Labs

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1197 on: October 27, 2018, 02:07:08 pm »
Maybe this has already been done before, but I compiled a composite picture of my actual board with superimposed component labels, and also differentiated which parts are directly related to the DAC, and others near by that are not directly related, but also show signs of corrosion. In my mind this should make it easier to positively identify all the critical parts that set the DAV reference voltage (current).

Wanted to add the DAV reference voltage testing points as well, but not yet sure where they are. Will add once I located these.

There is also one additional part shown with a red label that does not match the location as seen on the service manual parts layout for this area, but it seems more to the left. Maybe board changes that where only documented in later service manuals. I am using service manual PN 070-6863-00 last revision Sept 1989.

If I made any mistakes, please let me know so they can be corrected.
« Last Edit: October 27, 2018, 02:09:51 pm by AMR Labs »
 

Offline cheeseit

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1198 on: October 27, 2018, 05:14:01 pm »
Try to find 070-6863-01 which is newer, preferably the searchable version.
 

Offline AMR Labs

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1199 on: October 27, 2018, 07:20:12 pm »
Board wash!

Took quite a bit to get the crud around the 3-4 most affected resistors, had to repeat with several wash cycles.

Done gently with dish soap and a soft toothbrush.
 


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