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Classic II chimes - screen with thin broken vertical lines

nvdeynde

Well-known member
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 ?


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nvdeynde

Well-known member
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.
 

nvdeynde

Well-known member
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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