800 Ram Slot 2 not working - some help please?

[KLund1]

Hi,

   I got an 800 with odd behavior. It will not boot with any Atari ram in slot 2.

I have pulled the whole machine apart and have only the base plane, and power board out and connected. I have done the usual. cleaned the slot and board. Re-seated all the base plane chips, and ram module cards.

With only 1 16K ram module in slot 1, it boots. I put in a SS2.07 cart in and tested all 3 16k ram modules. They all pass. I have switch all 3 16k to all positions and no change, it will not boot with anything in slot 2. They all boot in slot 1. I have swapped out the OS and CPU boards with several other known goods one I have on hand. No difference. Well, no, sometimes I get a yellow full screen, or a full black screen.

I have reflowed the slot 2 joints. no change. I tested the LS chips in a little tester I have they all show as good.

I put some Deoxit in the slot, no change. I looked for any physical damage with a 10x glass but saw nothing alarming.

I put a Practical Peripherals MM1632 ram card set for 16K in slot 2 and it booted, but only shows in SS2.07 as 24K. So it looks like a 8K card. 

Oh, all testing done with a 16K in slot one, of coarse. I often swapped slot 1 ram with another 16K just to make sure it was not that card.

 

Any ideas why it is doing this? Possibles fixes?

[Faicuai]

Do you have an extra 800 MoBo (known-good) laying around? (preferably of same revision, or Rev9 at minimum)? 

[KLund1]

Yes. I have a working exact same Rev A board. Well just tested it and it does not read the Return key. It works fine on the bad slot 2 board

Whats your thoughts?

Edited September 24, 2021 by KLund1
update info

[Faicuai]

27 minutes ago, KLund1 said:

Yes. I have a working exact same Rev A board.

Whats your thoughts?

Good.

 

Here's what I would do if I were right on your shoes:

1. Prepare and assemble (stand-alone) extra MoBo with CPU, ROM and (x2) 16 KB boards from troubled machine, together with Powerboard, keyboard and (optionally) speaker.
2. Locate every single supporting-logic chip of troubled-board (EDIT: south of OS-slot) and transfer-and-test to stand-alone board ONE-at-time. Check system-boot check every time you transfer an individual chip.
3. If problem does not appear / confirm on stand-alone board, then transfer (one-by-one) Pokey and PIA (I don't think they are related, but just in case).
4. If problem has NOT yet appeared on stand-alone board, I would be very inclined to think that you have physical-damage on Port-2 edge-connector and/or traces (not easily seen) on troubled MoBo.
5. Last but not least: bring @ClausB into the operating room. If there's someone who could suggest a different or more effective way to trace this issue, it would be him.

My 0.02c

 

 

[ClausB]

Try swapping in the 74LS42 or LS32 from the working board. They are the only chips with different signals between slots 1 and 2.

 

Reseating all the chips might help.

 

Edited September 24, 2021 by ClausB

[KLund1]

I fond the problem! The was a staple jammed under ram lot 1! The kind of staple from a desk paper stapler. Only about 2mm were visible. It was stuck under, from right to left, pins 11 and 12. It was making contact with the slot pins and a via there.

But I mean this was fully jammed under the black plastic. I had to pull hard to get it out. I have no idea how it got in there. But I'll bet that is why this machine was retired back in the day.

Well it works great now. Another 800 saved!!!

Thanks everyone for the help and advice. Always very much appreciated!

[Faicuai]

15 minutes ago, KLund1 said:

Well it works great now. Another 800 saved!!!

Bravo!! WELL done!

 

????

[+kheller2]

"Atari, yeah we've got that!"

[Sugarland]

11 hours ago, KLund1 said:

The kind of staple from a desk paper stapler.