Another (new) 130XE boots to red screen

[woj]

So that would be i/o 0-3 pins, and a0-a7, correct? I will try to give it a go.

 

EDIT: OK, so this is interesting. First, I have little clue on how to calibrate the oscilloscope, so I just made sure it shows me a rough signal. The a0 through a7 seem to be healthy on both chips. IO2 also. IO0 looks OK on the first chip, it's stuck at 5V on the second (the spectrum is variating a bit, but generally stuck to the top). IO1 is at 5V on the first chip, at 0V on the second. And IO3 is the reverse of IO1.

 

I am no specialist, but I clearly need to finish testing the RAM by swapping them around.

 

Edited August 28, 2022 by woj

[woj]

Right, so I had a moment today when I thought I won this, I desoldered Basic and with Option it booted to Self Test, I ran the memory test and it stopped during ROM testing (to be expected I guess), then rebooted and the old story again. Earlier today I though it's a good idea to recap it so I ordered the capacitors, now I think it's even a better idea.

[woj]

While waiting for the parts to arrive, I need an opinion on another thing. Looking at the documents out there, and also the Santos' new board details, I was convinced the bypass capacitors for RAM should be 100nF, regardless of the memory type (1 or 4 bit), but on my board they are actually 220nF (marking 224). Does this make any difference? I know the ceramic ones do not have to be replaced, yet i managed to disturb those while removing the RAM chips, so I will put in new ones anyhow, but the question is should I use 100nF or 220nF?

[xrbrevin]

looking at the service manual, for your board it shows 1uf

see page 24
do yours look like theyve been desoldered?

 

130xe Hardware Manual.pdf

[woj]

I don't know, you tell me, the best picture I have is in post #3 up there. I think it should be .1uF, not 1uF, all those bypass capacitors marked u1 in this document are 0.1uF on all other schematics I have seen. Anyhow, so that would  be another thing to try, I need to take them out anyhow.

 

EDIT: looking at some other pictures I made I can also see that the soldering job on some of the other bypass capacitors is really poor, so yet another thing to check...

Edited August 30, 2022 by woj

[TGB1718]

42 minutes ago, xrbrevin said:

looking at the service manual, for your board it shows 1uf

Bypass capacitors would never be as high as 1uf, 0.1uf is pretty standard at these frequencies

Edited August 30, 2022 by TGB1718

[xrbrevin]

yes i did wonder - 100nf/0.1uf is my initial thought but the book of words said otherwise!

[woj]

OK, so there are some developments, but I am still nowhere and now even more confused to be honest. I will take some shortcuts here through all I have done yesterday and today. First I corrected some suspiciously looking solder points on bypass capacitors here and there, then memory and Basic sockets arrived, soldered them, the computer worked in 65XE mode, for quite a while, got to load Lasermania several times and all. Then I started shuffling the memory chips and during SelfTest it crashed. Going back to the initially working configuration did not solve the problem.

 

From that point on I do not get any red screens anymore, it either boots and works for some seconds (gets to test OK several RAM squares in SelfTest), and that is only after it has been powered down for at least 10 minutes or so. Or it boots to black screen if I do not wait. This is both as 65XE with any selection of RAMs and as 130XE with eMMU. It also seems that the longer it rests the longer it works afterwards. With this constant state I also replaced the memory capacitors from 220 to 100nF ones and recapped all electrolytic ones. Checking after every batch of 2-3, the state was always the same and so it is right now.

 

I pretty much eliminated eMMU and Basic, not too sure about RAMs, it can still be that only 1 is OK. Clearly, something either does not like to get warm for longer period of time, or charged. Working on this assumption, how would I go about identifying what...?  

 

My biggest worry is that there is some weak point / trace on the board, and that I will probably never find...

 

Nth edit: one more thing - can I piggy back the bypass capacitors in the attempt to find a possibly faulty one?

Edited August 31, 2022 by woj

[woj]

One thing I forgot, somewhere in the process of my later trials the screen got greenish when it does boot, but I am quite sure (not 100%) it was OK after recapping. I know there is a pot that I can use to correct this, but I am quite sure I did not touch it and I think this happened on its own.

 

And I was just studying this service manual, the schematics there say the bypass capacitors for RAM should be 100nF, however, the board picture in that very same manual clearly shows different capacitors and they seem exactly like what I had on the board. I think I should do some more experimenting here...

 

 

 

[Beeblebrox]

This thread is quite long now so not really time to read it all.  You have clearly done a lot of work.  Been there before many times myself.  For my own 130XE fix journey as linked/detailed in my signature I found I went around the houses a lot before finding the problem(s). It may or may not help to read my post as might be something in there that helps.  Most of the time I've found it's more likely to be bad ICs and traces/vias than passive components at fault.  

 

Best thing I ever invested in was the sys check ii diagnostic unit from Tf_hh. 

 

Most of the issues I've encountered are bad ram or failing ICs.  I've probably fixed around 20 A8s over the last 2 years or so.  (By no way an expert though). 

 

Good luck. 

[woj]

Thanks, I will do the reading (not that I am not doing it all the time ;)). SysCheck is on its way to me. The spare 130XE for parts is still not fixed though (the potential seller is very unresponsive). Yes, the traces or badly soldered vias are my worst fear...

[woj]

One brilliant thought I had was to check how much power the computer is using and whether it goes up (or down) when it crashes. So I hooked up the multimeter (that got me into trouble later, see below) and also tried my old trusted converted PC power supply to check if also that would change anything. Nothing profound here, the computer takes 0.59A in both states. After the first crash I did manage to start it up again without too much waiting several times for it to crash again on me after a few seconds. The crashes were of different sorts, for example, the keyboard was reading wrong keys first,  later the screen started to flicker / loose sync. None of the boots survived more than 20 seconds.

 

Another thing I tried was to bridge an extra 220nF capacitors over the memory power supplies. No changes. 

 

Then when the computer was still sort of working / screen flickering I took the multimeter in the attempt to quickly check the voltage on different chips. I flipped it to 20V DC, BUT FORGOT to put the red lead back in its place. I started with the power socket on its back, as soon as I touched the two poles there was a tiny spark and the flickering screen went black. At that point I almost had a heart attack (if you ever fried an expensive peace of electronics like I did before in my life, you know the feeling). Immediate reboot gave nothing. I waited a bit and also swapped the two RAM chips and it then booted again, though very short. So a small relief (though I cannot be 100% sure that no extra damage was done). 

 

Does this little adventure give any more hints as to what can be wrong?

[woj]

It seems the next order of business is going to be redoing the GTIA socket. Still working on it yesterday I think I have seen the flickering being sensitive to touching in the OS ROM / GTIA area, so went on to re-flow the OS ROM with solder a little bit (had to be done anyhow for desoldering at some point) and remembered that I also did that to the GTIA socket the day before and that was probably when the screen got greenish and I got new symptoms. So I cleaned up everything again around GTIA and OS ROM, and also re-flew the transistor that sits nearby. All that brought back the nice blue color on the next boot! Still crashed though, but now I know I should not be proceeding without revisiting the socket and seeing what's underneath it. I also now know it gets better with low temperature, rather than something being charged, this morning the computer worked for longer than usual and we have it a bit chilly at our place at night. 

[Beeblebrox]

You may have done this throughout and I realise I am stating the obvious but the general rule,  where possible, is do one thing at a time and check if it made a difference. Socketing multiple ICs or doing multiple things obviously means you cannot pinpoint any changes/progress or more importantly any new issues arising. 

 

Also I had a hell of a time fixing one of my A8s (an 800XLF) where I was getting lots of instability much like you are experiencing and after fixing a few other issues that came to light and having no joy it turned out to be an almost imperceptible break between a top of the pcb trace and a via under the ram chips which broke the line of all the ram chips.  

 

See here 

 

 

 

[woj]

38 minutes ago, Beeblebrox said:

You may have done this throughout and I realise I am stating the obvious but the general rule,  where possible, is do one thing at a time and check if it made a difference. Socketing multiple ICs or doing multiple things obviously means you cannot pinpoint any changes/progress or more importantly any new issues arising. 

 

Also I had a hell of a time fixing one of my A8s (an 800XLF) where I was getting lots of instability much like you are experiencing and after fixing a few other issues that came to light and having no joy it turned out to be an almost imperceptible break between a top of the pcb trace and a via under the ram chips which broke the line of all the ram chips.  

 

See here 

 

 

 

 

I am trying as much as I can to limit myself to doing one thing at a time, though it's very difficult for me (against my usual way of working ;)), or at least have a clear plan on the steps to take and not diverge from that plan. 

 

One thing is for sure - I have not done that much to the board yet (socketed GTIA, socketed eMMU, socketed RAM, socketed Basic, recapped the electrolytics, changed 5 other capacitors). Somewhere on the way it got from non-work (red screen) / work state to more frequently working, but with disturbances / flickers. Either some IC is unstably braking down, or something I did changed the state of affairs, hence it makes sense to go back and revisit. This is also under a more likely assumption that I got a fully healthy computer to begin with.

 

Anyhow, thanks for the support, it helps me not to do something stupid.

 

[mimo]

30 minutes ago, woj said:

 

I am trying as much as I can to limit myself to doing one thing at a time, though it's very difficult for me (against my usual way of working ;)), or at least have a clear plan on the steps to take and not diverge from that plan. 

 

One thing is for sure - I have not done that much to the board yet (socketed GTIA, socketed eMMU, socketed RAM, socketed Basic, recapped the electrolytics, changed 5 other capacitors). Somewhere on the way it got from non-work (red screen) / work state to more frequently working, but with disturbances / flickers. Either some IC is unstably braking down, or something I did changed the state of affairs, hence it makes sense to go back and revisit. This is also under a more likely assumption that I got a fully healthy computer to begin with.

 

Anyhow, thanks for the support, it helps me not to do something stupid.

 

That is actually quite a lot, and lots of potential to cock things up. THe XE boards are notorious for being very poor quality and it is really easy to damage or lift a trace on them. Also, why change the caps? It is pretty rare for an Atari to have failed caps even now.
Personally I would wait for syscheck to arrive and then try and troubleshoot some more. 
Some decent photos of your work, front and back , may help someone diagnose further 

[woj]

Don't have all of the pictures, but some, will post them separately by IC. First the GTIA after desoldering. Any traces / pads that did not look ideal after the process were checked with multi-meter. (I should have probably checked them all unconditionally). 

Edited September 2, 2022 by woj

[woj]

eMMU (yes, the cotton swab left a lot of crap, I cleaned that up later). And yes, I can see the two legs bridged, but they are supposed to be connected anyhow, so I left it as it was.

Edited September 2, 2022 by woj

[woj]

Basic

[woj]

And memory. Yes, the capacitors and their joints got damaged in the process, they were replaced.

[woj]

I completely redid the GTIA socket (precision sockets are a bitch to remove I found out), checked everything underneath it thoroughly, cleaned up everything. Connections / pads / vias are all OK as far as I can tell. This did not change anything, still working after cold boot, then starts to misbehave, then goes to screen flickering. Pictures attached, they are actually B&W. Those resemble the symptoms Beeblebrox pointed me to above in his thread, so I need to check that thread again. Sometimes during this flickering when in Basic it seems that computer also gets random key presses (or effectively behaves as if), not really sure if that gives any additional hint. 

 

I am at the point of indeed having to wait for SysCheck, new RAM, and the donor machine to arrive. The acquisition of the latter is still not finalized, but I made progress. 

[chevymad]

Have you tried cooling chips with air duster yet?

[woj]

17 minutes ago, chevymad said:

Have you tried cooling chips with air duster yet?

You reminded me that I was supposed to look for my other half's can of it, I found it now, unfortunately it was practically empty so did not get to check too much. I will get a new one tomorrow. 

[Beeblebrox]

Not sure if you have already but are you happy PIA and also Pokey are OK? 

 

Also I recall one of my A8s had an issue with one of the pins on antic plus also a transistor was bad. 

 

On my mobile at mo so can't easily check but look at my resurrected 130xe thread again in my sig (and maybe the 600xl one too) -  I think it was with the 130XE. 

[woj]

9 minutes ago, Beeblebrox said:

Not sure if you have already but are you happy PIA and also Pokey are OK? 

 

Also I recall one of my A8s had an issue with one of the pins on antic plus also a transistor was bad. 

 

On my mobile at mo so can't easily check but look at my resurrected 130xe thread again in my sig (and maybe the 600xl one too) -  I think it was with the 130XE. 

No, I have no clue yet about either Pokey or PIA. Yes, I am reading your topic, Q3 is one thing, and then the manual also suggest U2, U19, U20.

 

The problem here is that not only I get messed up picture, but also the computer is non-responsive, so it's not just video output...