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Mac Plus bad IC / Logic chip?

zezba9000

Well-known member
So I was given this Mac Plus that came with two motherboards. One fully working and the other boots and works but the image on the screen is waky.
As you can see in the image, I get a flashing disk that blinks with a cursor etc. I know this isn't a screen issue as I can test it with the working motherboard & screen is perfectly fine.

Question is, is there a known IC chip on Mac Plus thats for video output that can cause this?
Or something else?

1634530624553.png

None working motherboard is in very good condition otherwise.
1634530776753.png
 

just.in.time

Well-known member
Have you tried swapping the RAM from the known good board to the board with the graphics issues? Usually RAM issues will throw a sad Mac, but maybe in this case it’s presenting as graphics issues.
 

zezba9000

Well-known member
Have you tried swapping the RAM from the known good board to the board with the graphics issues? Usually RAM issues will throw a sad Mac, but maybe in this case it’s presenting as graphics issues.
Yes the same ram was used between both boards. It must be something with the board itself.
The fact that the bad board functions but just the scan lines are jumbled makes me think its some IC chip (maybe a bad cap causing it?) that could be effecting vertical sync line timings.
 

mg.man

Well-known member
I'd try re-flowing the solder joints on the connector for the cable that attaches the logic board to the analog board.
 
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