Installed 74F08 in 800XL, machine no longer boots

[magnusfalkirk]

I was reading through this thread last night and this morning after I ran across it in the forums. So it's been two months since you last posted about this. Have you been able to get the 800xl working again or is it just dead?

Edited January 15, 2023 by magnusfalkirk

[+x=usr(1536)]

11 hours ago, magnusfalkirk said:

I was reading through this thread last night and this morning after I ran across it in the forums. So it's been two months since you last posted about this. Have you been able to get the 800xl working again or is it just dead?

Long story short, I had to halt work on the 800XL at the end of last year.  Time being what it was, I felt it was better to pick up work on it again this year.

 

No major progress, but after some further troubleshooting I'm fairly certain that it has a bad delay line IC.  There is a 64K SRAM module sitting here waiting to go in, but the 256K upgrade that's in there now has to be reverted before that happens.

 

If the SRAM module goes in and everything works, I'll probably just leave it in there and add a U1MB to it.  Been meaning to do that anyway, so this is a convenient excuse for taking care of that.  Haven't had an A8 with more than 64K for the last six or seven months, and while it's not a huge problem, it's been inconvenient at times where I'd rather it wasn't.

[+x=usr(1536)]

Tonight was going to be the SRAM module installation, and I got as far as removing the old 256K upgrade and getting the SRAM board in place.

 

Where it got interesting was in chasing down good points to pull the CASINH and EXTSEL signals from.  CASINH was fairly straightforward, but when I probed EXTSEL at pin 9 of U18, the other probe brushed against another wipe on the socket that should not have had continuity.  Several others also showed continuity where there should have been none. Probing around the board revealed +5V and GND are shorted at their respective rails.

 

This is interesting, because despite having specifically tested for this condition before (and more than once), this is the first time it has shown up.  The machine wasn't tested after powering it up a couple of times over the last few weeks, so I don't know how long this issue has been there and I just hadn't noticed it, or if something with an intermittent problem finally let go.

 

Anyway, next plan of attack is a recap and replacing transistors.  If nothing else, that will at least eliminate them from the equation.  A visual inspection shows no solder bridges anywhere, but confirming that with a continuity test isn't really possible until the short is taken care of; readings are just too suspect until the board is routing power as it should be.

[woj]

Thermal test of any sort?

[+x=usr(1536)]

9 hours ago, woj said:

Thermal test of any sort?

Nothing's becoming alarmingly warm.  My concern right now is that one or more of the custom ICs may be shot, but I'll cross that bridge if / when I come to it.

 

The only one I'm majorly worried about is POKEY, but this machine had been swapped to Rev. C BASIC, the OS ROM was replaced, Rockwell CPU replaced with a Synertek, etc.  Not huge stuff, but things I'd rather not have to re-do.

 

Assuming that the machine comes back up and runs properly, it will be getting a U1MB.  At this point, I really have no excuse not to.

[magnusfalkirk]

What's the latest progress on this 800xl? Have you had the time to work more on it or has life interrupted? 

[+x=usr(1536)]

55 minutes ago, magnusfalkirk said:

What's the latest progress on this 800xl? Have you had the time to work more on it or has life interrupted? 

Life has most definitely interrupted.  Components are sitting here waiting to go in; it's just a question of finding the time to be able to sit down and replace what needs to be replaced.

 

We are getting some snow right now, so hopefully the next couple of days will have enough cancellations in them that I can poke at the 800XL instead of doing actual work 

[magnusfalkirk]

Wish we'd get some snow out this way, though from watching the weather forcast last night ob Channel 9 we are liable to get some snow/ice mix tomorrow morning. Will be curiouswhen you get the Ultimate 1MB put in, I'm think about having that done to my 800xl. Stay warm, stay safe.

[+x=usr(1536)]

28 minutes ago, magnusfalkirk said:

Wish we'd get some snow out this way, though from watching the weather forcast last night ob Channel 9 we are liable to get some snow/ice mix tomorrow morning.

It's largely been gritty sleet here.  Not quite actual snow, but definitely not hail, either.  About all it's really good for is icing up the roads.

29 minutes ago, magnusfalkirk said:

Will be curiouswhen you get the Ultimate 1MB put in, I'm think about having that done to my 800xl.

Once this thing is fixed and back to something approaching normal, I'll start figuring out that side of the equation.

29 minutes ago, magnusfalkirk said:

Stay warm, stay safe.

Thanks - you too!

[+x=usr(1536)]

Got a bit of a start on the next round of troubleshooting and recapped the machine.  Haven't tried booting it yet, because round two is coming, and that one is transistor replacement.

 

Continuity testing of the 2N3904 and 2N3906 transistors shows all of them to be shorted.  Base to emitter, base to collector, or emitter to collector, it doesn't matter - every single one of them will pass current if you put a probe on any two of its pins.

 

What's interesting is Q7.  This transistor is an MPSA55, and is the only one on the board that isn't a 2N3904 or 2N3906.  It's also shorted, and is now obsolete.  There weren't any near-enough equivalents that I felt comfortable with using (it's used for cassette drive motor control, so don't want to burn it out), but there are quantities still available.

 

Assuming no interference from the weather, components should be here by the weekend, and with any luck will be installed shortly thereafter.

[_The Doctor__]

??? how are you testing these transistors?

[Dysphoria]

Not to add anymore work to your plate on this, but I did experience a similar, difficult to trace, issue when working on my 130XE. The system was not booting, and was giving me either a black or a very dark green screen. I ended up checking all resistors against their stated values, and found several to be outside of spec. I replaced the ones I identified as bad and the machine booted right up. I hope this helps.

[+x=usr(1536)]

6 hours ago, _The Doctor__ said:

??? how are you testing these transistors?

Via diode testing from base to both emitter and collector, followed by emitter to collector.  This is done in both directions.

[+x=usr(1536)]

4 hours ago, Dysphoria said:

Not to add anymore work to your plate on this, but I did experience a similar, difficult to trace, issue when working on my 130XE. The system was not booting, and was giving me either a black or a very dark green screen. I ended up checking all resistors against their stated values, and found several to be outside of spec. I replaced the ones I identified as bad and the machine booted right up. I hope this helps.

Good point.  FWIW, all resistors have been continuity-tested (and passed), but not specifically tested for resistance as they're still in-circuit.  This is something that's on my radar, but given the sheer number of them on the board I'd prefer to not start chasing that down until the transistors are taken care of.

[mickster]

10 hours ago, x=usr(1536) said:

Got a bit of a start on the next round of troubleshooting and recapped the machine.  Haven't tried booting it yet, because round two is coming, and that one is transistor replacement.

 

Continuity testing of the 2N3904 and 2N3906 transistors shows all of them to be shorted.  Base to emitter, base to collector, or emitter to collector, it doesn't matter - every single one of them will pass current if you put a probe on any two of its pins.

 

What's interesting is Q7.  This transistor is an MPSA55, and is the only one on the board that isn't a 2N3904 or 2N3906.  It's also shorted, and is now obsolete.  There weren't any near-enough equivalents that I felt comfortable with using (it's used for cassette drive motor control, so don't want to burn it out), but there are quantities still available.

 

Assuming no interference from the weather, components should be here by the weekend, and with any luck will be installed shortly thereafter.

This is very very very very very very unlikely.  I don't know what you are doing wrong and I think its great you are trying to fix this on your own, but there is no way that many parts have failed in this process.  Most likely there is now a compound circuit board issue due to broken traces/bridged connections/poor soldering when changing components/sockets/removing chips.

 

At this point, if you really want to fix this on your own. It would require using an o-scope and checking for proper signals (the easiest way would be to use a working computer to compare signals).  

 

Sorry, I don't mean to be a buzzkill

Edited February 1, 2023 by mickster

[+x=usr(1536)]

25 minutes ago, mickster said:

This is very very very very very very unlikely.  I don't know what you are doing wrong and I think its great you are trying to fix this on your own, but there is no way that many parts have failed in this process.

Unlikely, yes.  And I'll be the first to admit that this is the shotgun approach to the problem(s).  More:

25 minutes ago, mickster said:

Most likely there is now a compound circuit board issue due to broken traces/bridged connections/poor soldering when changing components/sockets/removing chips.

Haven't found any broken traces or bridged connections.  Soldering checks out for continuity.

27 minutes ago, mickster said:

At this point, if you really want to fix this on your own. It would require using an o-scope and checking for proper signals (the easiest way would be to use a working computer to compare signals).  

A working computer, I can do.  An oscilloscope, nope.  Working with what I have in this case - and I know it's stone knives and bearskins, but it's what I have.

28 minutes ago, mickster said:

Sorry, I don't mean to be a buzzkill

Not in the least.  I've been through this machine fairly extensively at this point, and am going through each potential step as others are eliminated or confirmed.  Totally open to other ideas, but resources are limited for now.

[_The Doctor__]

so you de-soldered the components for testing? it is the best method.

Edited February 1, 2023 by _The Doctor__

[Dysphoria]

4 hours ago, x=usr(1536) said:

Good point.  FWIW, all resistors have been continuity-tested (and passed), but not specifically tested for resistance as they're still in-circuit.  This is something that's on my radar, but given the sheer number of them on the board I'd prefer to not start chasing that down until the transistors are taken care of.

FYI - resistors can be measured in-curcuit. Capacitors, on the other hand, are more difficult to test in-circuit.

 

Yes, there are a lot of resistors, I ended up replacing six or so of mine. I believe they were all in the areas that impact video output. I printed out the Sam's pages that showed which components were resistors and went through each one. I wrote on the print-out for each one what the expected and actual values were. I then found the ones that were out of spec (there's a percentage range to consider) and replaced them.

Edited February 1, 2023 by Dysphoria

[+x=usr(1536)]

32 minutes ago, _The Doctor__ said:

so you de-soldered the components for testing? it is the best method.

Not all of them.  Until spares were on hand, they had to be tested in-circuit.  Removing and subsequently testing them so far has jived with what I've found in-circuit.

[+x=usr(1536)]

35 minutes ago, Dysphoria said:

FYI - resistors can be measured in-curcuit. Capacitors, on the other hand, are more difficult to test in-circuit.

True on both counts.  I'm not a fan of taking values from anything while it's in-circuit, but I will generally check them for go/no-go conditions (e.g., shorts and opens) without removal.

35 minutes ago, Dysphoria said:

Yes, there are a lot of resistors, I ended up replacing six or so of mine. I believe they were all in the areas that impact video output.

And it's entirely possible that there are problems in the video neck of the woods.  However, given that there's continuity all over the board where it shouldn't be, chasing that down is my first priority.

35 minutes ago, Dysphoria said:

I printed out the Sam's pages that showed which components were resistors and went through each one. I wrote on the print-out for each one what the expected and actual values were. I then found the ones that were out of spec (there's a percentage range to consider) and replaced them.

Yup, that's been my SOP.

[_The Doctor__]

continuity all over the board usually tracks back to a bad component central to those groupings. tearing everything out and replacing isn't anything but a way to take small issue and turn it into cans and cans or worms. The thread is getting long in the tooth and going back to read what's actually been done is becoming problematic.

 

It's usually a shorted RAM chip, Cap, or support component. Most terrible calamities can be seen by heat, discoloration, etc. The big problem is all the destruction as a soldering iron is dancing all over the PCB shotgun style... the dead component bodies will pile up even though they might have been living beforehand.

 

I had a board that testing showed as half the bus being dead and couldn't find a pulse on that half with a logic probe. Oh it must be a bad LSI a bad crystal, solder bridge, or breaks/ blah blah blah... no it was a single bad RAM chip. It was in common to everything else, where as other stuff was only in common to smaller sections. Procedure and logic is testing and troubleshooting must. The shotgun approach normally leads to dead components and PCB's

Edited February 1, 2023 by _The Doctor__

[+x=usr(1536)]

13 minutes ago, _The Doctor__ said:

The thread is getting long in the tooth and going back to read what's actually been done is becoming problematic.

TL;DR: it's broken 

13 minutes ago, _The Doctor__ said:

It's usually a shorted RAM chip, Cap, or support component.

RAM has been removed from the board.  Caps have been replaced.  Supporting components TBD.

13 minutes ago, _The Doctor__ said:

Most terrible calamities can be seen by heat, discoloration, etc.

Of which there is none, nor has there been any.

16 minutes ago, _The Doctor__ said:

Procedure and logic is testing and troubleshooting must.

If you haven't read the rest of the thread, how would you know what has already been done?

[mickster]

2 hours ago, x=usr(1536) said:

A working computer, I can do.  An oscilloscope, nope.  Working with what I have in this case - and I know it's stone knives and bearskins, but it's what I have.

 

O-scopes can now be bought for $140 from amazon.  There is also plenty of tutorials on youtube (adrian's digital basement is a personal favorite).

 

Best bet is to unsolder any sockets you have installed and check the board with a magnifiers headset (also can be bought from amazon very cheaply).

 

At this point, you shouldn't be worried about video output at all.  After checking for circuit board damage, next step is checking for Clock signals, then reset, then address buss, then data bus.

 

Shotgunning is not your friend at this point.  In fact, every time you pick up the soldering iron, the problem becomes more complicated than before.  I know you said you have checked your work, but most likely you have not found your mistake.  If a working pcb no longer works after changing a chip,  then its 99% labor failure not other components.

 

Also the fact that changing the Sally changed your video output doesn't really mean that Sally was bad.  If the data/address buss is messed up, different chips can cause a different 'locked up' state.

 

I cannot stress enough that this is not a component failure, but circuit board damage.  It is fixable since its such a simple pcb. 

 

Once again, if any of this seems negative, I really don't mean it that way.  Have fun trying to figure out.

[_The Doctor__]

I read the thread and found the pellets from the shotgun off putting, it's peppered with a method that makes me cringe and can't follow.

 

It's unclear what tools and diagnostic equipment you have at your disposal, the number of dead components does not make sense and is staggering. Usually when there is a catastrophic failure of shorts etc, there is evidence of too much voltage and current passing through the components and or circuits, not always mind you but usually at least one thing or another shows that stress. Based on all I am reading, the common point is the soldering gun/iron/pencil. I have a bad feeling the patient was on life support and the surgeon is committing murder. I hope to help you, but don't know how. Others have commented but all are met with rebuttals.

 

I hope someone can find a way to help you save the Atari in your care. Please list what you have to work with, and others can suggest the best way to use what you have and possibly convey what you need to do an effective, and more efficient job.

[reifsnyderb]

Hello,

 

I didn't read through everything.  Since the first thing you did was install a socket, I'd remove that socket and thoroughly inspect the board.

 

The 74LS08 (or 74F08) affects the Phi0, Phi2, the Light Pen line, and your CAS Inhibit/PB Extsel.  Most likely the original problem is related to Phi0, Phi2, and/or the CAS Inhibit/PB Extsel.  Other troubleshooting could have caused other problems, of course.

Edited February 1, 2023 by reifsnyderb