Intermittent memory failures on 800XL

[TZJB]

11 hours ago, Sid Pokey said:

Firstly, I don't remember what it was that plopped into the cartridge port - some foodstuff perhaps - but it's been there for decades.

 

And secondly, it's not corrosion on the power switch legs. It seems to be an insulation coating. It's supposed to be black.

 

And as for the residue on the seam to the shield on the right hand side, note how it ends abruptly. Liquid damage wouldn't do that. My assumption is there used to be some sort of glue that's long since dried up.

 

One issue is though as TZJB pointed out, something looks amiss around C74 to C77. Plus also to a lesser degree further down (C102+?). Assume they're capacitors?

 

All this though is on the right hand side which I'm assuming has little to do with the RAM. Maybe that's why I had the original problem with SIO port connectivity though?

 

The corrosion looks worse in this picture. C77 & C78 can be removed permanently as they sit across the DATA IN and DATA OUT of the SIO and are often removed to increase SIO speed. C77 sits across SIO DATA IN and looks bad so may have caused your previous problem. The others are more involved with the joystick ports.

 

[TZJB]

Just to add that the liquid damage looks similar to cola which might explain the discolouration of the capacitors, and it seems to extend downwards towards the other capacitor bank which are also discoloured. It could just be they need cleaning with IPA and they are all fine though.

 

The rear of the board does not indicate any modifications since manufacture so the DRAM is factory fitted from what was to hand!

 

There is a small sign of the liquid reaching the rear of the board near J6 but nothing seems to be damaged there.

 

I finally found C42 next to GTIA and it looks okay to me except for being physically larger than similar 100nF de-coupling capacitors. I also see some scratches on GTIA, the deepest being near pin 40, probably from removal in order to clean the contacts?

[_The Doctor__]

I'd make sure there was no trace/track damage under the LSI chips that were pried out.

[Sid Pokey]

11 hours ago, TZJB said:

 

The corrosion looks worse in this picture. C77 & C78 can be removed permanently as they sit across the DATA IN and DATA OUT of the SIO and are often removed to increase SIO speed. C77 sits across SIO DATA IN and looks bad so may have caused your previous problem. The others are more involved with the joystick ports.

What type of capacitors are they? And are they of a type that can leak?

[351cougar]

all those caps are ceramic, looks like they put a SM part into a leaded case . The "" leaky type are alum elect type , metal cans either radial or axial lead. C79 to left of the others . 

[TZJB]

On 5/8/2024 at 9:03 PM, Sid Pokey said:

What type of capacitors are they? And are they of a type that can leak?

 

The small glass capacitors are of the ceramic type which do not leak, so it is not the capacitors that have leaked in your 800XL.

 

The electrolytic capacitors in Atari 800XL computers do not tend to leak either.

 

 

[Sid Pokey]

Hello OP here with an update on the outcome.

 

The short version is I got me a chip puller tool, yanked all the socketed chips (which doesn't include the 'failed' RAM), gave them all a contact cleaner treatment, and hey presto, up to yet (fingers crossed), the ye olde 800XL is purring as good as new. And finally I've been able to put the new SDrive Mini to the test, and a lovely bit of kit it is too. Batheing in nostalgia!

 

I also got some IPA to clean up all the supposed liquid residue you all spotted on the controller side of the board. Oddly though, whatever it is, IPA hasn't budged it. I'm still convinced it's adhesive of some sort that's probably always been there. Nothing short of sanding will shift that.

 

Also did the S-Video chroma mod. Albeit only one TV I have supports S-Video which it not the TV I use. And I'm gonna have to make up a cable to even try it out. But hey, might as well do it while I've got it apart.

 

Might have a couple of follow up questions, but I'll do that in a separate post.

 

Thanks to all that contributed. 👍

[TZJB]

16 hours ago, Sid Pokey said:

Hello OP here with an update on the outcome.

 

The short version is I got me a chip puller tool, yanked all the socketed chips (which doesn't include the 'failed' RAM), gave them all a contact cleaner treatment, and hey presto, up to yet (fingers crossed), the ye olde 800XL is purring as good as new. And finally I've been able to put the new SDrive Mini to the test, and a lovely bit of kit it is too. Batheing in nostalgia!

 

I also got some IPA to clean up all the supposed liquid residue you all spotted on the controller side of the board. Oddly though, whatever it is, IPA hasn't budged it. I'm still convinced it's adhesive of some sort that's probably always been there. Nothing short of sanding will shift that.

 

Also did the S-Video chroma mod. Albeit only one TV I have supports S-Video which it not the TV I use. And I'm gonna have to make up a cable to even try it out. But hey, might as well do it while I've got it apart.

 

Might have a couple of follow up questions, but I'll do that in a separate post.

 

Thanks to all that contributed. 👍

 

That is great news that your 800XL is working again. It is strange that the staining cannot be resolved.

 

I did the S-Video modification too, and I don't have an S-Video display to try it on either.

 

As I suggested previously, removal of C77 & C78 is advisable in order to prevent clipping of the waveforms on the serial bus.

 

Does your 1050 disk drive work now too?

 

Removal of the four serial bus capacitors in the 1050 is also advisable, again to prevent clipping which will improve speed throughput on the serial bus.

 

Capacitors to be removed are marked in red in the image below.

 

 

 

Edited May 26 by TZJB

[Sid Pokey]

3 hours ago, TZJB said:

 

Does your 1050 disk drive work now too?

 

Removal of the four serial bus capacitors in the 1050 is also advisable, again to prevent clipping which will improve speed throughput on the serial bus.

 

Yeah, the 1050 seems to be working fine too. Did have a question about whether I can use a 1050 and an SDrive at the same time though - initial trials suggest not - but I was gonna put that in a separate post after more testing.

[nasty niff]

Set 1050 to D2 and use D1 on a sdrive.

[Sid Pokey]

38 minutes ago, nasty niff said:

Set 1050 to D2 and use D1 on a sdrive.

Doh! Yeah, of course. Obvious. Will play with it more. Thanks.

[Beeblebrox]

30 minutes ago, Sid Pokey said:

Doh! Yeah, of course. Obvious. Will play with it more. Thanks.

Just make sure all machines are off before plugging and unplugging SIO cabkes or power cables. Sounds obvious but it's so easy to forget and cause damage.