Tektronix 2465B oscilloscope teardown

[S57UUU]

These old Motorola processors could easily be overclocked by a factor of 2. In the 80's I had a Tandy Color Computer, which was based on an 1MHz 6809 chip. Worked with double clock frequency perfectly, never encountered any problem. Probably wouldn't work in the whole military temperature range, but room temp +-10 degrees, not a glitch.
So running a 4MHz type at 5MHz, shouldn't really be a problem.

[DavidAlfa]

Found several comments and a PDF repair guide stating the -8V cap (C1101) shouldn't be replaced with anything else than 100uF, or the voltage would be affected.

I fully recapped several PSUs (Including C1101) without any issues, had a bag of EEU-FC1E471 caps, which are Panasonic 470uF 25V low-esr, measured~30mOhm, where old ones did ~1ohm.
Replaced all the 20V & 40V caps with these, as highest voltage is 15V, there's plenty of room till 25V.

I only kept the original 100 & 160V caps, also the 100uf one under the big HV ones (At mains side), it only performs a startup delay,  470uF there would make the PSU to delay for 5 seconds.

Additionally, the 15-ohm resistors on the mains input (Paralleled with NTCs/PTCs) were blown in most PSUs, replaced with 2W parts.
Those near a regulator in a corner, also 15R, were ok but toasty, so I replaced them too.

Voltages were perfect afterwards, (7.98 ... 8.02V), with much lower ripple and noise than before.

Did this for 5x 2465A/B, calibrated them all (Most also had dead NVRAM), and returned to work in great shape.

Now I have 2x 2465B and 1x 2465A with poor focusing (Fully recapped, they were non-starters, some caps's legs had dissolved!), but no amount of tweaking will fix it, it's like looking through a misty/foggy window.

One 2465B had the CH1/CH2 preamp hybrid damaged, causing signal distortion, so I removed it from the lower spec 2465A, it was the blurriest one anyways.

Now I have two blurry 2465Bs, one worse than the other, any hints?
Voltages are perfect, so it must be something elsewhere.... tomorrow I'll swap different boards/hybrids, at least I will shorten the search circle.

Obviously, CRT and plastics were thorougly cleaned!

[Mark Krass]

Interesting.  It does look very factory.

Well, it's not going to stop working at 4.01 MHz, but it may not work properly at some of the operating extremes, such as temperature and supply voltage.

You could double check that pin 39 (EXTAL) is 5MHz, but I can't imagine it would be anything else.

Maybe it's from a mis-labeled batch and Tektronix was told by Motorola?  Or maybe Tektronix qualified them in-house themselves for 5MHz knowing the scope's operating constraints?

Thank you all guys who responded to my question. I checked pin 39, it has 5MHz indeed. Thus MC6802P, at least middle 90s production works fine with overclocked freq 5MHz. Well noted)

[Vince]

Hello people,

I apologize if my query is out of place here, but I was directed here.

Apparently this thread covers not just the 2465B ?

My question : I recently bought a 2465, a vanilla 2465, not a 'B' or anything.

It's got s strange cooling setup which appears to have many recurrent  / known issues.
I have all of them and I am trying to solve them one by one..

My problem for the day is to replace the dead DIP package transistor array, with discrete transistors (I guess arrays aren't available anymore ? Or at a high cost maybe...).
I gather people do that.
However I don't have any transistors in stock that have the appropriate current rating.

The array was rated at 1.0A which made sense since the control board runs on 15V and the current limiting resistor in series with all the emitters, is specified at 15R hence 1A total short-circuit currente in the motor windings. However the resistor on my board, measures more like 10.5ohms not 15, so I would need transisotrs rated at 1.5A or 2A.... AND that have a pin layout that can work with the board layout, that is with the base being the middle pin.

So to save me time, could someone tell me what transistors people use in this context ?

If that's out of place just tell me, I will create a new thread instead.

[DavidAlfa]

Yeah should work. I fixed one of these in a signal analyzer, a relay coil shorted out and burned one of the transistors in the array.
I simply cutted the pins and soldered a 2n2222A.
Any decent npn bjt like bc547 should work, I doubt each transistor in the array can handle 1amp?
Otherwise use a beefier one like the BD137 etc?

[Vince]

Nope the BC547 is a tiny 100mA 1092 jobbie.

BD137 I do have in stock and would be ideal, so I did try to use it but failed because of the base is not the middle pin so it won't fit the board layout.
This style of package does not allow you to swap pins like you can on small signal transistors.

The middle needs to be the base or it just won't fit, hence why I was asking what people have sucessfully used on this particulat application / board, to save me from scouring dozens of random datasheet on-line until I find one with a suitable pinout...

Array : it's a CA3725. Yes the 1A current rating is for each individual transistor. The array is specially designed to handle high currents to drive windings.

[DavidAlfa]

Ok! The one I fixed was driving a 70ohm coil with 5V if I remember correctly, so it was ok for the job.

[Mark Krass]

Hello
Need advise from experienced users.
Tek 2465B along with readout information started to output some artefacts to the display. Can't upload the video right now, but they are clearly seen at photos, attached. They are on signals area and are flickering 3-5 times per sec. When I turn readout intensity knob to the middle position they go away with readout info. Channel independent, even with grounded. Temperature also independent, coming up with cold device and go away with turning off readout only.

Now close to the point. I have another A5 board taken from a scope. When replaced - all is working fine, no problem, no artefacts. So the issue is in A5.
In original A5 board there was well known electrolytic caps leakage. All were replaced, potential damaged areas were inspected, cleaned. Proximate smd resistors, ceramic caps, traces are checked. Tantalum caps checked. Wima caps also checked.

Another point is that when I touch by finger test point TP32 (on readout schematic <7>) artefacts stop flickering and look like exactly at the photo. This is dot cycle generator section in readout schematic.

So this is the situation. What do you recommend to do?

[DavidAlfa]

Huh never seen that. But check for everything where the leaky capacitors did their thing.
I had found several resistors and caps falling open, their soldering tabs were no longer making contact with the internals after playing with the acid.
You might have missed some.
Also, did you lift all nearby ics? The electrolite will seep under them and dry.
I found lots of deposits under them, also some vias that looked pretty bad.

[AMR Labs]

When you repaired your A5 board, did you wash the (usually two) cap leak affected areas of the board? In most cases there will be some residual electrolyte left from the leaking caps on the board itself, and gently washing with liquid dish soap (Dawn, Palmolive, etc) and a soft tooth brush dipped in water, and then rinsing it off with water afterwards is the only way to effectively remove it. But be very aware that using IPA (70-90% Pharmacy Alcohol) to try and clean the board will only spread the electrolyte further around and it may slowly then over time once again start causing tiny corrosion problems in other nearby areas. I would also look for any signs of blue-green stuff left on or between any IC pins or vias that you may have missed. Use a microscope if you got one. On my board there where plenty of tiny bluish spots on those ICs located on the side under where there is only the one leaking cap. Don't have the SM in front of me so right now can't give specific PNs but I think you will understand what I mean.

Perhaps the problem you are seeing is related to a spot where electrolyte is creating an unwanted conductive leakage path that is causing those "ghost" images of the lower readouts to appear further up on the middle of the screen. One can see their horizontal positions seem to roughly match both lower readout displays. The fact that those ghosts are also flickering may further suggest that some signal from the readout generator is leaking from one area into another causing some sort of conductive bridge that causes this interference, and that still keeps a timing relationship with the actual readouts. But at least you where able to confirm that the problem is on A5, so no elusive wild goose chase on the rest of the scope. That is half the work, just to determine and confirm where inside the scope the problem is actually located.

See attached pics of my own A5 board showing the two main areas (at least in my case) that are usually affected going through the "car wash", and those should ideally be gently scrubbed and washed and then rinsed off (once again only use liquid dish soap) to make sure no electrolyte residuals are left on the board. Perhaps only washing the board if you have not done so already might clear the problem. Shake off any excess water left on the board and in between parts, and then be sure to give the board ample time to dry before trying it out. Here in the tropics I usually just need to put the board out in the sun for an hour. Some people like to "bake" the board in an oven at very low temperature, but in that case be very careful of not overdoing it. Perhaps even a hair dryer, but again, always be very mindful of not applying excess temperature.

[Mark Krass]

Hello guys,
Many thanks for your response! I removed and resoldered a few nearby ICs and have not found signs of acid. I washed these 2 areas in IPA only, and as I can see now that was not enough and was not right at all.
Ok, will wash it liquid dish soap as you suggested. If it does not show results I will start to remove-wash-resolder all nearby ICs.
Will let you know the progress.
 

[Mark Krass]

Hello,
Updates on the issue. I washed the board with water and dish soap. Dried it. Repeat this process 3 times. No effect.
I desoldered U2965, 2970 and 2890 and nearby ceramic caps, cleaned all area, explored with microscope and I can confirm that the tracks and pads there are ok. I replaced these ICs and caps with new ones and soldered them back. Cleaned the whole area one more time. No effect.
At this moment I can confirm that this "ghost leakage path" is not located at top & bottom layers.
I am out of ideas...

[AMR Labs]

So perhaps a faulty component then? I am unfortunately not very qualified to give detailed troubleshooting advice on the A5 board, I am not even very familiar with the circuit structure or schematic as I was fortunate not having to dig in very deep into it to get mine working again after clearing all the corrosion. Perhaps some other more experienced members here could give you further advise.

I would also try posting at the Tekscopes and Tekscopes2 IO groups, there are some very knowledgeable people there, some even are ex Tek employees from when some of these scopes where actually manufactured back in the 80s and 90s.

https://groups.io/g/TekScopes2

https://groups.io/g/TekScopes

Make sure to try both groups. Tekscope2 was formed at some point by a bunch of members that where not too happy the way the group was being run and decided to form a separate one. Tekscopes2 is usually my fist go-to place, but both are very good sources of information and helpful people if you ask the right questions and provide ample relevant supporting information so they can try to point you into the correct direction to pinpoint the issue.

And please keep us updated here of any progress.

[Orange]

Hello
Need advise from experienced users.
Tek 2465B along with readout information started to output some artefacts to the display. Can't upload the video right now, but they are clearly seen at photos, attached. They are on signals area and are flickering 3-5 times per sec. When I turn readout intensity knob to the middle position they go away with readout info. Channel independent, even with grounded. Temperature also independent, coming up with cold device and go away with turning off readout only.

Now close to the point. I have another A5 board taken from a scope. When replaced - all is working fine, no problem, no artefacts. So the issue is in A5.
In original A5 board there was well known electrolytic caps leakage. All were replaced, potential damaged areas were inspected, cleaned. Proximate smd resistors, ceramic caps, traces are checked. Tantalum caps checked. Wima caps also checked.

Another point is that when I touch by finger test point TP32 (on readout schematic <7>) artefacts stop flickering and look like exactly at the photo. This is dot cycle generator section in readout schematic.

So this is the situation. What do you recommend to do?

Check resistor R2890 on <7> ( on output of gate U2890B) If that one is drifted or open it would explain the 'finger trick' The diagram says 1k for the value.
Perhaps the electrolyte has affected the value

Edit : updated the resistor value to 1k

[Mark Krass]

Check resistor R2890 on <7> ( on output of gate U2890B) If that one is drifted or open it would explain the 'finger trick' The diagram says 1k for the value.
Perhaps the electrolyte has affected the value

Edit : updated the resistor value to 1k

Thank you. I checked R2890 when I was resoldering that area, its value is 332 Ohm and match the numbers on it. Mistake in SM.

Earlier in this thread I found an interesting case when electrolyte acid from C2965 has got inside U2890 and damaged its crystal. Not my case since I tried to replaced U2890 with no effect for me.

[Mark Krass]

Update on 2465B readout problem:
Ghost images start to appear only at the fast sweeps - 1us and less.
Also I've found that on slow sweeps signal trace and readout are alternated, see the shot attached.
No description of these symptoms in SM & charts but may be somebody faced such problem before?

[Orange]

Update on 2465B readout problem:
Ghost images start to appear only at the fast sweeps - 1us and less.
Also I've found that on slow sweeps signal trace and readout are alternated, see the shot attached.
No description of these symptoms in SM & charts but may be somebody faced such problem before?

Just as a quick test you can try to readjust the CRT GRID bias a bit and see if you can turn away the ghosting...

If that is not solving the problem, I think you need to start probing around on the readout system circuitry. Sometimes by connecting a probe (x10) will give you an indication which part is sensitive for this issue. There is a lot of CMOS on this board, a damaged output can also give you this effect.

Obvious something with the timing of the blanking signals is causing this. I'm afraid there is no easy way to get a simple solution with this problem, other than measuring and trying to nail it down.
The service manual has a decent amount of information in it, but it is very complex......

[AMR Labs]

Just a though, if the OP said that replacing the A5 board solves the issue, why would he want at this point to start poking around in other parts of the scope? Just my 2 cents.

PS. I just went by Tekscopes2 group and happy to see that you are getting pretty good engagement specially from Chuck Harris which I would say is the most veteran "fixer" of 2465/67 scopes as has been doing that as a professional service for a very long time so he knows them inside out, and the info you get from him is usually the very best. Other members will also provide good input and ideas, but Harris is the main reason of why I suggested going to Tekscopes2 first.

[Mark Krass]

Found a bastard!!!
U2965 had unconnected pad. I checked the area under this IC several times with microscope and there was no any signs that the problem was there!!
Today evening I decided to desolder all area around C2965 and check one again everything with tester now. And wow!!! Got it.
After repair this pad scope is running fine, readout is excellent, no flickering, no ghost images!
Interesting thing is that without that connection readout worked few minutes after power up and then dimmed and disappeared. Each time after power up. It looks to me that it was not heat issue, but readout circuit logic shut it down after getting problem with it. Who knows...

[AMR Labs]

Good job, feels great finding the culprit, doesn't it?
Enjoy your scope.

[calibrationfixture]

Hi Mark Krass,

Congratulations with your fix. A bit overdue, but U2965 does ring a bell with me and I checked my Repair Log.

Some time ago I replaced the 4 SMD Elco's on the A5 Controller Board of a 2445B (H706020). Before and after this it was working fine. The vast SMD replacement job on SG5030's made me look again to 24XXB Series A5 Controller Boards. On the aforementioned 2445B I noticed corrosion on U2965 and U2890 (74HCT00DT's). With their removal two heavily corroded Pads came loose. U2965 Pad 8 and U2890 Pad 7 (= GND). Based on the Electrical Diagram I made separate Wire Connections. After that Fix the Scope had no Read-Out. The Controller Board of this 2445B has 671-0965-05 as PN. The Service Manual refers to 671-0965-00 as PN and no updated Electrical Diagram as MCI. Comparing the 05 with a 06 Board from a 2467B (B052372) made clear that Pin 8 of the U2965(C) must be connected to Pin 9/10 of U2890(C) and not to Pin 5 of U2890(B) as with the 671-0965-00 Board. After this correction Read-Out was fine again.

Also on Tekscopes there is a Post on this (2465B, U2965, readout).

Calibrationfixture

[Mark Krass]

Hi Calibrationfixture,
You're absolutely right - pin 8 of the U2965 must be connected to pin 9/10 of U2890. I had to figure it out by myself taking out ICs from a PCB. Mine is SMD 671-0965-00 as well & SN>0500000. However SM for this revision is inaccurate in many areas of A5 schematic.
PS My lesson learned in this troubleshooting is to trust your multimeter, not your eyes! 
-Mark

[tonedeak99]

What an informative thread. Thank you Bravo and all the others who contributed here. Im the happy owner a 2465A CT and I wanted to follow the advice of many here and recap the PS. Especially get those RIFAs out before they pop. Not sure if I should replace any other caps besides those. All my J119 DC voltages are within spec. I also have no error messages and scope appears to be working pretty good. My calibration waveform seems a bit noisy at certain timebases since the trace is not a thin line but a thick fuzzy line. Maybe that’s normal. 🤷‍♂️

Also wanted to replace the Keeper II battery. Its reading 3.3v but dont want to risk losing my data.  What’s the best method for attaching a backup battery while doing the replacement?  I found these two online:
https://jestineyong.com/tektronix-2465a-dv-oscilloscope-memory-backup-battery-replacement/
https://cdn.hackaday.io/files/1638907011869760/Piggyback%20batt.JPG

Also I would be using my grounded soldering iron.  Could that be a problem if the A5 board is out of the scope?  Would it be possible that the iron would ground the battery and the EAROM would lose its data? 

Lastly as a backup plan I was thinking of backing up my data with the a GBIP adapter which was mentioned in this thread. Maybe using the NI USB model. Has it been confirmed that it can be used to backup and fully restore the EAROM data in case I accidentally delete it during the battery replacement?

Thank you all!

[factory]

The temporary battery question for the NVRAM was asked here too;
https://www.eevblog.com/forum/testgear/tektronix-2455b-ram-battery-replacement-advice-needed/msg5277409/#msg5277409

The electrolytic caps in the PSU sometimes leak conductive electrolyte over the boards, as well as eating the traces, this can cause expensive failures all over the scope when the PSU malfunctions. YMMV

David

[AMR Labs]

The electrolytic caps in the PSU sometimes leak conductive electrolyte over the boards, as well as eating the traces, this can cause expensive failures all over the scope when the PSU malfunctions. YMMV

Been there done that on my 2465B. If I remember correctly the usual leaking caps where the two (blue) 180uF 40V, and the (also blue) 250uF 20V ones, all to be replaced with 330uF 50V. Thing is sometimes you won't see the leakage pooled up under the cap until the cap itself has been pulled, but if the case make sure to clean well before installing the replacement. The green caps are usually still good, but while you are in there...

Also keep in mind the orientation error for one of the caps on the PCB silkscreen, which is reversed. Best to replace only one cap at a time without using the silkscreen as a guide, and making sure to take notes of each cap's orientation before pulling it so as to install it exactly the same way the original was. Also when taking notes don't confuse the 10uF 100V with 100uF 10V (I think it was) as both will look almost identical in size. I did that mistake when I followed my own bad notes and ended up getting a loud POP which was the only thing that finally revealed the mistake, as I was still checking everything against my notes and could not figure out what was wrong. Not sure the silk screen error applies in your case with an earlier 2465ACT, but certainly it does in the 2465B. You can find plenty more information on this error here on this thread, plus recommended capacitor shopping lists, etc.