Macintosh Classic with horizontal lines on screen

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Joined: Apr 27 2022 - 10:32
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Macintosh Classic with horizontal lines on screen
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I have a classic Macintosh board that was really damaged by the acid. I'll start by saying that I washed it carefully, replaced all the capacitors and restored the missing connections. There are connections between the CPU, ROM and BBU, the Mac turns on, it doesn't bong. and it shows horizontal lines on the screen, looking at the board with the thermal imager the chips seem to heat up normally (I compared it with a working motherboard), I also tried to remove one of the integrated RAMs and it gives me a sad face so I think the cpu and similar and also the video part is ok otherwise it wouldn't show the sad face, does anyone have any suggestions?

k24a1's picture
Last seen: 3 weeks 2 days ago
Joined: Mar 8 2022 - 09:44
Posts: 11
suspecting RAM chips

if you've removed one of the RAM chips and it gives you a sad mac, definitely want to check those. they could have been damaged from the acid leak, or the traces leading to those might need to be looked at. you'll have to replace them with 4x256Kbit DRAM chips like the ones on the board already. while i can't really read sad mac codes and know what they are off the top of my head, i do believe its RAM related. also you may wanna check other traces and make sure those aren't damaged.

Last seen: 13 hours 4 min ago
Joined: Feb 27 2021 - 18:59
Posts: 498
The error code displayed

The error code displayed (when you removed a RAM chip) is the expected error.




$000EFailed Data Bus test. The Z field indicated the bad bit(s) as a 32-bit mask for bits 0-31. This may indicate either a bad SIMM or data bus failure.

In this case, the mask "0x0F" is the 4 lowest bits on the data bus, corresponding to the RAM chip that was removed.

The puzzle is how to explain why this "Sad Mac" display demonstrates normal video output, but with the chip in place you get horizontal lines.

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