Tektronix 2430A halts

[kavea]

Hi all,
I'have bought a Tek 2430A from ebay in order to repair it and get myself a digital oscilloscope. The problem with this scope is that it halts during (at the end of) the Self Test procedure (picture below). I have found a service manual for this version and there is actually a repairing procedure for this case (page 202, "System uP halts in power test"), however i still can't figure out what doesn't working .. What i have done:

1/ Checked all voltages (except for CRT but it works), they are all ok
2/ Visual inspection: nothing special, a part some traces of flux on some boards, i guess someone have already replaced some components
3/ There is no Dallas NVRAM, it is an HM62256 and the battery is seems to be  ok (3.5 V)
4/ All caps seems good, i have desoldered two of them on a processor board and they where ok (all nichicon brand)
5/ Replaced some logic and OpAmp: U940, U422, U414
6/ Checked the ACQDN signal at U670, seems to be there (U670 is quite hot by the way, is it normal ..?)
7/ Checked the Interrupting circuitry, seems ok
8/ I noted that the waveform 3 (U942, pin 2) doesn't work, it still at 5V instead of dropping at 2.5V during the boot, but it still provide a good (high level) /RESET signal to the system uC (U640) , so i don't know..

BUT.. since i have only an analog Tek 2225 i couldn't check the real shape of the waveforms because it doesn't trigger in almost all cases, so i could just check if there is some activity or not..

If anyone have an idea of whats going wrong I would appreciate any kind of help to troubleshoot this scope

SERVICE MANUAL : http://kripton2035.free.fr/Resources/TEK2430A_serv.pdf

VIDEO:

[tautech]

Welcome to the forum.

There will be others that might have had this problem before so please be patient.
In the meanwhile a little more study for you:
http://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdf

[siggi]

I don't have any experience with the 2430A, but I fixed a pretty far-gone 2430 at one point.
First thing is that you MUST have a bench fan blowing over the hybrid heat sinks when you run'er open. You WILL otherwise damage the hybrids, which are getting pretty hard to find.

Do you have a link to the service manual that you can share?

The 2430 (and other scopes from the 2400-series) counts out the tests it's performing on the front-panel leds. I assume your 2430A does the same thing, as detailed in your service manual?  Where does it stop? Does it always stop at the same place?

Have you checked the LV power supplies for ripple as well as DC value? This is always first port of call, as if the supplies are wonked, just about anything can go wrong.

There are several diagnostic aids in this scope, including a service jumper that cycles the CPU through the entire address space. This allows you to see whether the address bus is good, look at the address decoding logic, and to see - to some extent - whether the bus drivers are good.

[kavea]

Welcome to the forum.

There will be others that might have had this problem before so please be patient.
In the meanwhile a little more study for you:
http://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdf

Thank you for welcoming and the pdf!

I don't have any experience with the 2430A, but I fixed a pretty far-gone 2430 at one point.
First thing is that you MUST have a bench fan blowing over the hybrid heat sinks when you run'er open. You WILL otherwise damage the hybrids, which are getting pretty hard to find.

Do you have a link to the service manual that you can share?

The 2430 (and other scopes from the 2400-series) counts out the tests it's performing on the front-panel leds. I assume your 2430A does the same thing, as detailed in your service manual?  Where does it stop? Does it always stop at the same place?

Have you checked the LV power supplies for ripple as well as DC value? This is always first port of call, as if the supplies are wonked, just about anything can go wrong.

There are several diagnostic aids in this scope, including a service jumper that cycles the CPU through the entire address space. This allows you to see whether the address bus is good, look at the address decoding logic, and to see - to some extent - whether the bus drivers are good.

Yes, i turn on the scope for maximum 1 min when it's opened , just during the time i measure the voltages. Of course, here is the manual of the 2430A :
http://kripton2035.free.fr/Resources/TEK2430A_serv.pdf

Actually the front panel leds doesn't show any error code sequence, but at the end when it halts the only led on is "+", and this behavior is always the same, it stops at the same step. The previous owner of this scope said that this problem has appeared progressively , it was stopping from time to time, but after off/on it was able to boot correctly. So i was thinking about capacitors, but they seems to be ok.

I have just measured ripple on the voltage supplies (picture), and i found something interesting (thank you sigi for this advice to measure the ripple). The ripple of the '-5V Ref' is 450 mV (!) This ripple is a sinusoidal signal of around 1 MHz frequency... Unfortunately the ripple of the -5V Ref is not specified in the manual, but i think it's not normal

[kavea]

I took a look on the circuit which generate -5V Ref, and all seems to be good. There is also a 'DC OK Sense' circuit which is LO when one of the power rail is out of spec (picture). In my case it's HI and voltages around the comparator are ok as well...

[siggi]

Yes, i turn on the scope for maximum 1 min when it's opened , just during the time i measure the voltages.

Cool - I used a CPU case fan for my 2430 pointed at the underbelly of the scope. That seemed to work fine.

Of course, here is the manual of the 2430A :
http://kripton2035.free.fr/Resources/TEK2430A_serv.pdf

Thanks, and ugh - I've never worked from a MIL manual . I understand they're written to a slightly different audience than your usual Tek service manuals. The schematic diagram scans are excellent, though.
Artek Manuals do have the 2430A on tap http://artekmanuals.com/manuals/tektronix-manuals/ if you get disillusioned with the MIL manual . Their scans are typically great, and they OCR the scans to allow searching.

Actually the front panel leds doesn't show any error code sequence, but at the end when it halts the only led on is "+", and this behavior is always the same, it stops at the same step.

See page 184, Fig 6-4 and the text around it. First all the TRIG LEDs should flash on, then they should count from zero up to the class of test going - is that not what you see?
They are then supposed to flash out the number of the test that failed, though if the MPU is halting, they won't get there. If you see only the +TRIG light lit, I think that means the 8000-tests started, but the 9000 did not.

The previous owner of this scope said that this problem has appeared progressively , it was stopping from time to time, but after off/on it was able to boot correctly. So i was thinking about capacitors, but they seems to be ok.

I have just measured ripple on the voltage supplies (picture), and i found something interesting (thank you sigi for this advice to measure the ripple). The ripple of the '-5V Ref' is 450 mV (!) This ripple is a sinusoidal signal of around 1 MHz frequency... Unfortunately the ripple of the -5V Ref is not specified in the manual, but i think it's not normal

Page 168, table 6-4 has the specs - 10mV peak-to-peak in 20MHz bandwidth. Finding a 1MHz sine on your -5V supply is highly unexpected - there'd have to be oscillation in the -5V regulation or some such.

Good luck!

[tautech]

If you look carefully at the 2 tables and compare your low ripple measurements against the Tek limits and some of the others look like they need investigation. 

Get all rails well inside the Tek ripple limits and you'll not have to revisit the PSU. 

FYI
High ripple can be a sign of a rail being overloaded, there's many things that can cause excessive loadings, dried out remote caps, Tantalums.....
Teck often have methods to isolate PCB's to assist finding the culprit/s.
RTFM. 

[siggi]

The ripple of the '-5V Ref' is 450 mV (!) This ripple is a sinusoidal signal of around 1 MHz frequency... Unfortunately the ripple of the -5V Ref is not specified in the manual, but i think it's not normal

Sorry - missed the "Ref" part the first go around.
If you're measuring this with a 1X probe, it's possible that your probe capacitance is giving the Ref op-amp indigestion. Try measuring with a 10X probe, or with a bit of resistance in-line with the probe tip (1-10K should do it, I'm told).

From the table of measurements, aside from the -5V ref - which almost HAS to be a measurement error (sorry:)) I don't think there's anything substantial wrong with your power supplies.

Can you post a video of the front-panel as the scope starts up?

[kavea]

Cool - I used a CPU case fan for my 2430 pointed at the underbelly of the scope. That seemed to work fine.

Ok, i have bought a small fan

See page 184, Fig 6-4 and the text around it. First all the TRIG LEDs should flash on, then they should count from zero up to the class of test going - is that not what you see?
They are then supposed to flash out the number of the test that failed, though if the MPU is halting, they won't get there. If you see only the +TRIG light lit, I think that means the 8000-tests started, but the 9000 did not.

Yes i have seen that page, but i can't find anything matching to my situation, even all trig led don't flash on, only three of them (all 5 leds are ok, they flash an error code when i disconnect one of the boards). You can see the video, i have inserted it in the first post.

If you look carefully at the 2 tables and compare your low ripple measurements against the Tek limits and some of the others look like they need investigation. 

If you're measuring this with a 1X probe, it's possible that your probe capacitance is giving the Ref op-amp indigestion. Try measuring with a 10X probe, or with a bit of resistance in-line with the probe tip (1-10K should do it, I'm told).

You're right, in x10 there is no ripple, ~25 mV in 20 MHz (i have borrowed a TDS210 from the lab where i'm working which have 20 MHz BW limitation)

I don't think there's anything substantial wrong with your power supplies.

I agree, i think it should be ok, it's a little bit out of specs, but.. considering the precision of my measurement tools..and 10mV of extra ripple should not disturb an old, good tek

Can you post a video of the front-panel as the scope starts up?

Yes:

I will take advantage of TDS210 to measure some digital signals, until tomorrow

[siggi]

Thanks for the video. I don't think your MPU is halted, IIRC the intensity pot is drive-by-wire, and you clearly manage to adjust the intensity. I think you'd need a fair amount of the digital stuff working for that.

Maybe you have FPP connectivity issues - have you tried giving the scope a few extra minutes, see whether it clears the problem step?

I couldn't offhand find another video of a good 2430A starting, and my 2430 is unfortunately not at hand, so I can't compare. Maybe we should try and take this over to the Yahoo TekScopes group - there's sure to be people there with a 2430A to compare against?

[guido]

The GPIB status led's stay off. On mine all three go on at boot for a few seconds. Than quickly only the middle and then left/right (hard to follow) and then all three on again for some more seconds. Then LOCK goes on during the rest of the self test. After this is finished, the SRQ led goes on.

I have it connected to GPIB, but the computer with the card is powered down.

Check around U754. Maybe it is broken and does also not reset gpib. If it is not selected it would be the main processor or address decoder.  And it does more, maybe the other outputs are important hanging the system if not working

[siggi]

The GPIB status led's stay off. On mine all three go on at boot for a few seconds. Than quickly only the middle and then left/right (hard to follow) and then all three on again for some more seconds. Then LOCK goes on during the rest of the self test. After this is finished, the SRQ led goes on.

Hey Guido, can you post a video for comparison - ideally with the GPIB disconnected to eliminate that as a source of confusion?

My guess would be the processor running the self test cannot communicate with the processor/chip running GPIB. Now why that would hang the system instead of just giving an error on the GPIB part and continue, i don't know.

IIRC the GPIB status lights have nothing to do with the GPIB interface chip at all - they're wired out from a register on the MPU data bus directly. Of course I can't find this in the schematic now, though...

[guido]

You are right. But Edited my reply already before yours. Page 346 of mil pdf. Buffer is controlled by system controller. But it has more outputs doing something. Seems to be dead or not driven in the video. Leds go on immediately after power up. Something is not right there. No need for comparisson video.

Ps i'm now

[kavea]

2 guido and siggi
I would like just tell that GPIB leds are working (flashing), but they have been disconnected. I will answer more tomorrow, it's late in Europe now

[kavea]

I think you'd need a fair amount of the digital stuff working for that.

Yes, the intensity is on FO-13 (p.313) then AOUT2 goes to the front panel uC (FO-8). But why there is a signal which appears when i touch the knob or the pin of AOUT2..

Maybe you have FPP connectivity issues - have you tried giving the scope a few extra minutes, see whether it clears the problem step?

If FPP is the ribbon cables i will check them may be of of them are broken

Check around U754. Maybe it is broken and does also not reset gpib. If it is not selected it would be the main processor or address decoder.  And it does more, maybe the other outputs are important hanging the system if not working

Hi guido, ok, i will check U754, but GPIB leds are working in my case, i forgot to reconnect the ribbon cable for a video. Can you tell me if your U670 (Time base controller, FO-16) getting hot ?  I'am a little bit worry about this chip. And of course if you can post a video of booting i would appreciate, in order to compare all leds (gpib, trigs)

I have checked the interrupting signal going to the system uC /IRQ and /FIRQ and they present some TTL signals which repetitively go from low and high. May be i should try to force them to high ?

[metrologist]

I have the same scope and that is exactly one of the symptoms I was seeing (OP video). I replaced the two metalized paper capacitors on the supply input and it fixed it, sort of. My scope now boots up and works fine for about a minute, then the display goes blank and it is locked (I don't remember what the front panel LEDs are doing). I measured the supply test points and they seem fine, so I've been stuck.

[kavea]

I have the same scope and that is exactly one of the symptoms I was seeing (OP video). I replaced the two metalized paper capacitors on the supply input and it fixed it, sort of. My scope now boots up and works fine for about a minute, then the display goes blank and it is locked (I don't remember what the front panel LEDs are doing). I measured the supply test points and they seem fine, so I've been stuck.

Hi metrologist,
Thank you for this information, you say one of the symptoms ? Which one exactly ?
About capacitors, you are talking about two red caps (picture) ?

[metrologist]

The caps will look something like this, and they are above the large blue filter caps between the metal framing and transformer (upper left area of your photo):

http://www.tedss.com/stock/images/2020/2020043902.jpg

2200 pF

I replaced the same caps on another Tek 2213 and that completely fixed it.

Mine was halting during self test and eventually showing the vertical bars. When I adjusted the horizontal, I could see a clipped waveform expand. I would get random self test errors. Most of the caps measured fine with an ESR meter, but I wonder if there is some leakage or other breakdown at higher voltage that I am not seeing.

[metrologist]

And now that I'm looking at your photo, I'm suspicious of that larger yellow block at the base of your arrows. I've forgotten what that is - if it is the same type of construction cap? Those metalized paper caps seem to have a reputation that precedes the aluminum electrolytics... I think the plastic polymer type caps last longer.

[Bud]

Did you re-seat the ICs, my 2430 got frozen during self-test and did all sort of funny things until i re-seated the ROMs and whatever i could find including interconnecting cables.

[kavea]

The caps will look something like this, and they are above the large blue filter caps between the metal framing and transformer (upper left area of your photo):

Thank you for the photos ! I have desoldered all of them , the red caps (68nF) seems ok , the paper caps are 3100 pF instead of 2200 pF and the yellow one (470 pF Phillips, mkt 344 hq, polyester caps) seems ok also. I will replace all of them to be sure.

Did you re-seat the ICs, my 2430 got frozen during self-test and did all sort of funny things until i re-seated the ROMs and whatever i could find including interconnecting cables.

I will do some poke test on IC's after replacement of caps

[lowimpedance]

I have an non 'A' 2430 which needed a power supply recap. After running for a bit it would also do weird stuff same as Bud's 2430 and the solution was to reseat the ROMs etc.
So I would highly recomemd the "IC poking" too and in particular the ROM area.
I find the 2430 an interesting beast and amazing how TEK crammed so many components in that casing!.
Good luck

[guido]

Showing a video without saying the GPIB LEDs were disconnected is not usefull. Puts people that are trying to help on the wrong track. So no, the buffer is not suspect if the LEDs behave as i've described.

There are already movies on the net, just search. E.g. .

I'm sure there will be more. You can also look out for similar models from the same range.

Seems it is more trial and error what you are doing. Try to follow the service manual troubleshooting guidelines. I'm guessing you don't have GPIB available? That would be my first try if the front panel isn't responding. But then again, i have GPIB controllers available.

Two caps left in the picture are evil. They will go bang. Not if but when. Red and yellow ones are normally ok.

But it could be as simple as a bad contact indeed. I've reseated the ROMs in mine too. Not that it was needed, but it is rather manditory when reading them with a programmer. And replaced supply caps and batteries.

When i look at your video you are already working on the controls when it is still testing. What happens if you just wait? Does it remain stuck in self test?

[kavea]

There are already movies on the net, just search. E.g.

Thank you

Seems it is more trial and error what you are doing. Try to follow the service manual troubleshooting guidelines.

Read the first post, the troubleshooting procedure related to the problem (picture) have been done from the beginning. Voltages and interrupting circuit have also been checked, after that what else can i do except "trail and error" ...

Two left caps are evil. They will go bang at some point. Always replace these types. Others should be ok.

Yes, i will replace the two left for the moment, their packages are cracked

[kavea]

To reseat the ROM's should i undo them from the sockets ? (i worry about the datas on these ROMs). I've bought all 5 caps and going to replace them after work