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Commodore PC 20 III works after 15 minutes

D

dippaolo

Member
Joined
Nov 20, 2017
Messages
17
Location
Poland
My Commodore PC 20 III does not work after turning on. The monitor shows nothing. When I leave it on for about 15 minutes, turning it on again works fine.

Supersoft / Landmark Diagnostic ROM's software also doesn't work at first, it freezes in a random place. After about 15 minutes, the test passes correctly.

Where to find the problem?
 
I know about computers stopping to work because parts run hot. But computers that first have to warm up before it will run ???

What I can think about is a bad connection, between an IC or even inside an IC, that expands a bit when warming up, thus creating a good connection. Hoe to find it? Use some cooling spray to cool various parts. If the computer stops, you have found the bad spot. Of course no guarantee at all that this idea will work.
 
I know about computers stopping to work because parts run hot. But computers that first have to warm up before it will run ???

What I can think about is a bad connection, between an IC or even inside an IC, that expands a bit when warming up, thus creating a good connection. Hoe to find it? Use some cooling spray to cool various parts. If the computer stops, you have found the bad spot. Of course no guarantee at all that this idea will work.
 
Yes, my computer needs to warm up :)

Watch the video on first run:
https://photos.app.goo.gl/qUbWJH8JoMamCNuc6


Watch the video after a few minutes:
https://photos.app.goo.gl/x5h8sJNfwKyR88vAA


See how it starts up after several minutes:
https://photos.app.goo.gl/o3EmwYbPPc7AzR5T8


I'll try your idea in a few days.

Maybe someone else will suggest something?

I still have a PC 10 III. I moved all the ICs from the second computer (the ones in the sockets) and there was no improvement. I updated the bios to the latest version.
 
Partially repaired.

A few years ago, I removed the batteries. Now I have looked closely. I fixed two connections. The computer starts right away.

However, I get the error "Bad ram at 8075D = 00h, expected = 00h".

About this next topic.
 
I had a PC that failed to boot completely when first powered up, sometimes took 2-3 attempts to get to POST. It was early sign of a pending video card failure. Problem went away when I replaced the totally failed video card.
 
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