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Innovative Leisure

Atari 520ST Screen Error

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I'm in the process of fixing up an early 1985 520ST. I have installed TOS, pushed in all the socketed chips and removed a touchy RAM expansion, and it has begun to show signs of life.

 

Lately upon booting, it's been scrolling random characters for a few seconds and then showing a black screen with a white border.

 

Has anyone else experienced this error?

 

 

P. S.: Thanks to adolobe for the ST, accessories and help with troubleshooting.

post-27442-0-70156000-1357981936_thumb.jpg

Edited by Innovative Leisure

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If the machine generally works but is flaky with time or temperature, it's probably one of the age-sensitive parts.

 

- power supply. check the DC out for AC ripple. if you can't do that, replace any old electrolytic capacitors on it if not done already. they dry out over time, esp. with raised temperature.

- electrolytic capacitors on the main board, especially any under or near the warm power supply.

- dry joints on the pcb. can be hard to find, a hot-air station can be used to reflow the solder in specific places if you can narrow it down a bit.

 

Remove any peripherals for debugging (e.g. floppy drive) since these can also be a source of problems and can stress the power supply even if the rest of the machine is working ok. When you're testing, make sure you always test the same way (same duration/ambient temperature) and use several tests each time - to avoid confusing yourself with erratic results.

 

The board can be tested with a non-Atari power supply (like a PicoPSU or ATX) to rule out PSU problems but it should be done with care (and use existing reference from others who have tried).

 

This is general advice - you could have other problems like a damaged IC socket, poor ground contact or something. It's best to have this done by somebody with the proper tools (i.e. scope, ic-safe continuity tester, solder/air station) and experience.

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That RAM expansion, was it 4mb? The ram on the motherboard may have been disconnected or jumpered if so.. (that is assuming it has never booted?)

 

You could try removing the socketed chips and cleaning the connects with isopropyl alcohol and a cotton bud, then leaving to dry for a bit before reinserting the chips (make sure they correctly orientated).. Was the RAM upgrade one of those that fits into the socket of or over the MMU and Shifter? I'd probably check those first. As this looks like an original ST, the floppy will be getting most of its power from an external PSU I think?

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Yes, the motherboard is a revision A with an external power supply and no built-in disk drive or RF modulator. The RAM expansion was an additional 512K piggybacked that connected to the MMU with 3 wires, got the same screen though.

Edited by Innovative Leisure

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After viewing pictures of various ST motherboards, I am now wondering if the MMU/or Glue on my ST may have been reinstalled the wrong way.

 

http://www.atari-forum.com/wiki/index.php?title=Atari_ST_motherboard_revisions

 

 

Glue and MMU from my ST:

 

http://i38.photobucket.com/albums/e111/TonyVisconti/IMG_0094_zpsc9ee2f0b.jpg

 

http://i38.photobucket.com/albums/e111/TonyVisconti/IMG_0098-2_zps33eb2d69.jpg

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After viewing pictures of various ST motherboards, I am now wondering if the MMU/or Glue on my ST may have been reinstalled the wrong way.

 

http://www.atari-for...board_revisions

 

 

Glue and MMU from my ST:

 

http://i38.photobuck...zpsc9ee2f0b.jpg

 

http://i38.photobuck...zps33eb2d69.jpg

 

Looks OK. That line or 1 on the board should be lined up with dot on the chip if I remember right.

So, it should be ok. If you have a puller you can take the chip out and I think there is a dot in the socket to show you what way the chip goes.

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Necro-bump!

 

Did you ever resolve this? I have a 520ST with the same behavior. Power supply is outputting proper voltages. Removed, cleaned with deoxit, and reseated all socketed chips. Gonna check each DRAM next.

Edited by mattsoft

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