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tezza
August 10th, 2010, 07:17 PM
Hi,

I was working my Atari 400 the other day. It was working normally for about three hours when suddenly the screen went like this:

http://www.classic-computers.org.nz/blog/images/2010-08-11-atari-no-boot-system.jpg

This is a random garbage screen but not a static one. The characters are constantly changing.

Before I poke around, has anyone seen this before? I have the Atari 400/800 service manual which has a diagnostic section. It mentions a grey/black, green/yellow and blank blue screen under catastrophic failures but not this symptom.

The screen looks like this with any cartridge and also no cartridge.

Tez

barythrin
August 11th, 2010, 08:59 AM
It's constantly changing on it's own or each time you end up at this screen? Does typing change anything?

tezza
August 11th, 2010, 12:32 PM
Constantly changing on it's own (very rapidly). Also, the bottom 1/3 of the screen is black!

I pulled it apart yesterday and swapped out some RAM to no effect.

Every chip is socketed which is good. Reseating didn't improve matters. There are quite a number of proprietory ICs, but hopefully it may just be a logic chip somewhere.

The PSU has a few small ceramic caps which should be orange but are green due to oxidation. I'll replace these but I don't think that's the problem. I haven't measured voltages yet, but there was no sign of any issues until this (suddenly) happened.

Tez

tezza
August 27th, 2010, 07:23 PM
Hi,

Just closing this up. It was the ANTIC chip. A replacement solved the problem.

Tez