TDS 784C suffering "ADataH stuck hi" error causing Acquisition Self Test fail

[Tony_G]

[Sorry I meant this to go in repairs but accidentally dropped it here, mods please move if desired]

Hi All,

I have a TDS 784C that fails the self test with an error in Acquisition. The full text of the error is:

ERROR: diagnostic test failure,  ADataH stuck hi,   Demux is 200

The service manual seems completely unhelpful in finding out where/what is the source of this error - I'm hoping that someone else may have run into it and can help shed some light on where I should start poking.

Thanks,

TonyG

[snoopy]

Check for dry joints on the 240 pin QFP demultiplexer chips.

Do a search for a thread I started on the TDS784A because I posted some images of what I found. Some people have also reported problems with faulty memory chips.

Also you may have to replace the relays in the attenuator boards. Most of mine were high in resistance and some were even open circuit !! This will only become an issue when you run a signal path compensation and it flags an error

cheers
david

[Tony_G]

Thanks - The post reminded me that I had aborted the SPC so I needed to do it again. Cleared out the Error Log, run SPC and then ran all the diagnostics.

Then again, it might be a dry joint because I may sure to have the unit well warmed up before running them (had it sitting and running for about an hour). I'll have to let it cool down and see if the problem comes back.

Thanks again.

TonyG

[james_s]

So I've come into possession of what I believe is this same instrument and while exploring the features I started to consistently get this ADataH stuck hi error and Acquisition reports Fail in the self test. From looking over the component service manual for the similar TDS520B I deduced that this likely means there's a stuck bit in the bus between the "C" ADC and the associated DMUX which so far as I can tell serves channel 3. Acting on suggestions I've seen to check solder joints on the DMUX ICs I decided to start there. Close inspection revealed a few suspect solder joints on the big QFP so I carefully reflowed some of those, inspected it for bridges and then fired it up. Scope still appears to work, I can get nice looking signals on all four channels but now I find that when I run *any* of the self tests, Processor, Acq, Display or Front panel it will run for a bit and then appears to reboot and display the splash screen that says Power on self tests PASS.

I'm at a bit of a loss here as to what is going on, could a problem I created on the acquisition board cause the whole scope to reset? I would have thought that any fault severe enough to cause that would prevent it from passing the power on self test. There are no new messages showing up in the error log, only the ones from before. The soldering I did on U200 looks fine, although I'm thinking I may xray it when I pull the board to replace the attenuator relays which I know need some attention. Replacing ICs with parts off a parts acquisition board is within my ability but I don't want to risk damage or dump money into what turns out to be a red herring, a used acquisition board would probably cost as much as I paid for the whole scope. Could the self test problem be a coincidence that developed? Seems unlikely as I didn't even touch the processor board. I believe I could swap in an acquisition board from a similar model scope for testing but given this has the 2M option my impression is that my choices of a proper replacement board are somewhat limited. Isn't 2M a hardware option with physically higher capacity acquisition RAM? I have not attempted any power-on probing, having seen dire warnings of catastrophic damage. It's a real ego-deflater to make negative progress, it's still a usable instrument but I don't want to invest in proper probes and such until I'm reasonably confident that it's working 100%.

[Tony_G]

Hey James,

That is in fact exactly the same scope. As I was mentioning, I powered this guy up and ran the self-test - That's when I got the ADataH error. Snoopy's suggestion on the relays led me to run SPC which showed the "Ensure the scope is warmed up before running SPC". I then let it warm up, ran SPC and then I ran the diagnostics again.

The scope passed the diagnostics (as you saw in the video) and passed SPC. After that I assumed the issue was addressed and put the scope on EBay - When I was asked to run SPC multiple times, that was when I saw the failure and removed the listing and relisted it as "For parts not working".

When you say:

now I find that when I run *any* of the self tests, Processor, Acq, Display or Front panel it will run for a bit and then appears to reboot and display the splash screen that says Power on self tests PASS.

Do you mean that you tell it to execute self-test and a little after that the scope reboots?

Does it look like this part of the video?

Self-test video

If so then the scope is working correctly because they reboot as part of self-test.

TonyG

[james_s]

Hmm I hadn't realized it was normal for it to reboot when running the self tests, I'm going to have to take another look at it tonight, it's possible that I have actually fixed the ADataH error, that would be awesome. I still need to replace the attenuator relays and that hopefully will fix the SPC failure. I knew going in that I was gambling and buying a project and paid accordingly so it's not the end of the world but I still really hope I can get it fully working. It's a beautiful instrument, faults aside I absolutely love using it. There's no way I could justify buying a scope this powerful for what a fully tested working one commands. It's *way* more scope than I'm likely to need on a regular basis but better to have more scope than I need than to need more scope than I have.

When I run the self tests I get the regular boot splash screen, there's nothing that shows the individual tests as having passed, is that really how these work? Just the lack of errors in the log? The screen is exactly the same as comes up on a cold boot. I've never used a TDS series of this era before so I have nothing to compare it to.

Looks like I'm going to have to invest in a GPIB interface to clear out the error log. At one point I powered it up with the acquisition board disconnected and that filled the log with all sorts of ominous errors.

[Tony_G]

That caught me out as well the first time I ran it on another TDS scope (the 754D I was telling you about) and I had to look it up.

Apparently the process is that the scope reboots and it will only display a dialog with things like:

PASS ++ Processor
FAIL ++ Acquisition
...

on it if there is an error - Otherwise if nothing fails in the self tests then if just starts up like normal. I guess they worked on the theory that if you didn't see the "FAIL" then there wasn't any need to go to the error log.

If you watch that video of mine you can see what a "passing self test" experience should look like. If you want I can lend you a GPIB adapter to use while you try and repair the device. Alternatively you can buy a 82357B clone on eBay for $100 right now or a new Prologix USB one for $150.

Let me know - You should still have my Cell number so shoot me a text if I can help.

TonyG

[snoopy]

Hmm I hadn't realized it was normal for it to reboot when running the self tests, I'm going to have to take another look at it tonight, it's possible that I have actually fixed the ADataH error, that would be awesome. I still need to replace the attenuator relays and that hopefully will fix the SPC failure. I knew going in that I was gambling and buying a project and paid accordingly so it's not the end of the world but I still really hope I can get it fully working. It's a beautiful instrument, faults aside I absolutely love using it. There's no way I could justify buying a scope this powerful for what a fully tested working one commands. It's *way* more scope than I'm likely to need on a regular basis but better to have more scope than I need than to need more scope than I have.

When I run the self tests I get the regular boot splash screen, there's nothing that shows the individual tests as having passed, is that really how these work? Just the lack of errors in the log? The screen is exactly the same as comes up on a cold boot. I've never used a TDS series of this era before so I have nothing to compare it to.

Looks like I'm going to have to invest in a GPIB interface to clear out the error log. At one point I powered it up with the acquisition board disconnected and that filled the log with all sorts of ominous errors.

I think if all of the tests pass then it doesn't display anything about the individual tests other than a pass. I just ran mine and that is what it did. Also there is a dipswitch on the board which forces the scope to run the tests every time it is powered on. Some people switch it off which can trick people into thinking there is nothing wrong.

These are great scopes. You won't get 4gs/s 1GHz bandwidth 4 channel scope for this price anywhere. With 1GHz active probes I use mine to verify SDRAM timing at 166MHz clock rate. Your 100-200MHz entry level scopes are more or less useless for this because of the limited bandwidth and probe capability. Also this scope has up to 250 Gs/s equivalent time sampling so even if you go past its limit of 4Gs/s on one channel you can still view waveform detail on repetitive signals. Not many scopes can boast this capability - not even the Agilents of the day or today for that matter ! Also InstaVu gives you waveform update rate of up to 400K waveforms/s so its perfect for capturing glitches. This scope is circa 1995 which is little wonder they cost 35K at the time I even bought another 744A for spare parts or a fixer-up

cheers

[james_s]

Yeah I tried watching the video but I couldn't really see the screen clearly on my phone so I figured I'd watch it at home later and also look for videos of other similar scopes. I did see that failure message before when it showed acquisition failure. So maybe this is in fact fixed, aside from the relays, I'm going to replace all of them while I'm in there.

I appreciate the offer to loan me an adapter but it seems like the sort of thing that might be worth buying myself to have on hand. Also I don't want you to feel obligated to mess with/suport something sold as-is. I see there are some $29 USB GPIB adapters on ebay, anyone have experience with one of those? There are also some crusty old ISA cards that are not very expensive, I have a lunchbox 486 I could put one of those in.

[TheSteve]

Check out this thread (on this same page at the moment) for a GPIB adapter you can build yourself for pretty darn cheap:

https://www.eevblog.com/forum/testgear/gpib-interface-(ieee488)/

[james_s]

Hey look at that, Arduino based GPIB, that's perfect as I have several of those Arduino nano clones for just such a project. I ordered a cable which I'll cut in half and build an interface.

I'm still tempted to look for another similar scope to have as a spare but I'm trying to resist that temptation. I'm trying to have less stuff in my house, not more! Broken/orphaned equipment seems to follow me home.

[james_s]

So I tried this again tonight, fired it up from cold and ran the self test right away. I think it is indeed working just fine, yay!      Now to start shopping for probes. I'm thinking some P6139A's look like a good economical choice for general use, then at some point in the future I can pick up a higher frequency active probe.

As expected, SPC still fails but new relays should resolve that, they should be here in a week or so. Do I need to use special solder on the ceramic hybrids?

[snoopy]

So I tried this again tonight, fired it up from cold and ran the self test right away. I think it is indeed working just fine, yay!      Now to start shopping for probes. I'm thinking some P6139A's look like a good economical choice for general use, then at some point in the future I can pick up a higher frequency active probe.

As expected, SPC still fails but new relays should resolve that, they should be here in a week or so. Do I need to use special solder on the ceramic hybrids?

I've heard of people using silver solder but I just used the ordinary leaded stuff as I didn't have any silver solder and it hasn't given me any problems so far. When you remove the relays it's just best to cut through the legs with long side cutters rather than try and unsolder them. Then unsolder the remaining legs. This will avoid lifting pads. When you solder new relays there is a particular order of soldering the four relays so that it is easy to get the soldering iron tip into the right spot without being fouled by the other relays. Also make sure you don't mix up the attenuator boards as the calibration will no longer be valid so I suggest you mark each one with a permanent marking pen of '1' for channel '1' etc and mark it on the frame as well.

cheers

[james_s]

I was thinking of using a hot air pencil to unsolder them, I did see the cutting method suggested so that's another possibility. Either way I'll be careful, those modules look terrifyingly fragile in pictures. I had the same thought about marking them, I'll make sure I do that.

[james_s]

So I built one of these nifty GPIB adapters using a cheap Arduino nano clone and it seems to work perfectly, total cost of about $10 and a half hour of my time. I cleared out the error log and while I was at it I enabled option 2C, a feature that appears to be completely useless unless I wanted to build an interface for a T1 line or some obsolete network interfaces but hey it was free so why not. I haven't explored what else I can do with this interface but it should come in handy.

Then I noticed that my option HD is missing, and indeed the hard drive no longer shows up in the file manager. Could I have disabled that somehow? I popped out the PCMCIA hard drive and tried it in an old laptop and it recognizes in the device manager but doesn't show up as a disk anywhere else, even the disk manager. Maybe the drive just croaked? Seems like an odd coincidence since I just used it the other night but I suppose that happens. I'm gonna pick up a PCMCIA to CF adapter and try that, I have a few old CF cards and some 4GB Microdrive hard drives.

[james_s]

Just to post an update on this, I finally had a chance to change out all the relays, that was a pain, very delicate operation with those ceramic hybrids. I had to make a custom tip for my soldering iron out of a piece of solid copper wire, I tried a hot air pencil but the ceramic substrate sucked away the heat. It took a few hours but when I wrapped it all up I was relieved to find that the scope is working perfectly. I ran SPC multiple times and it passed every time. Yay! 

[nctnico]

Well done! I hate doing repairs on ceramic substrates because they need lots of heat and you can mess them up so easely.

[Tony_G]

Great - What was the outcome on the HD issue?

TonyG

[james_s]

Well the HD still isn't working but I did order a 256MB PCMCIA SSD to try which hasn't got here yet. I tried all the CF cards and microdrives I have and couldn't get any of those to work. I need to make up a console adapter to see if it spits out any useful information at boot. While I'd like to get it working, the hard drive is not really all that useful anyway.