68kMLA Classic Interface

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Classic II chimes - screen with thin broken vertical lines

Posted by: nvdeynde on 2022-02-28 02:50:39 My Classic II suddenly stopped working. I hadn't used it for about 2 months and now upon power on it chimes but gives me a screen with thin vertical lines. It are not the caps: both analog and logic board are recapped. It's a logic board issue. The board is very clean and upon examination under a magnifying glass I can't see bad spots. So it chimes upon power on but that's it. It doesn't try to boot from it's FDD or HDD. All voltages are good as well. I have changed the Roms with a set of known good one's but that doesn't help either. Where can I start troubleshooting this issue ? I'm think possibly 1 or more broken address lines but between which IC's should I start testing and which lines ?

Posted by: bibilit on 2022-02-28 06:13:44 can be an Egret issue... pretty common when you have got a chime

Posted by: nvdeynde on 2022-02-28 08:02:03 I have checked all the pins of the Egret for continuity with the Bomarc schematics and they are all good. It can be the Egret chip itself of course but I don't have a spare one to test with. So it chimes at power on and when I press the interrupt immediately I get the death chimes which is normal behavior. It just doesn't get further in the startup sequence. The Roms are good as well.

Posted by: bibilit on 2022-03-01 00:02:56 The Egret can be connected but contaminated, happened to me a thousand times.

Posted by: ymk on 2022-03-01 00:38:58 The lines are 16 pixels apart. It looks like a bad data line.

Posted by: nvdeynde on 2022-03-01 10:24:13 This one is repaired. I had removed the Egret, cleaned everything up and put it back without result. Then I started with removing the Ram modules one by one and replace them with new chips. U14 was bad. After replacing that one the board worked again. There was no visible damage on the faulty ram chip or on the pads of the logic board. So just a faulty ram chip. Can you diagnose these issues with a scope so you know exactly where the problem is on the board as the same symptoms can have many different causes ?

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