Hello, I'm repairing a Macintosh Classic I picked up with battery damage. When I received it, it was totally dead (0V from the power supply on all rails), and it's battery had leaked on it's board. It has it's original SCSI drive and RAM expansion card with dual SIMMs.
I've since repaired it's power supply (4.95v for 5V supply, 11.82 for 12V supply), cleaned up the board, replaced all caps, and have been trying to get it to boot. Despite the battery leakage, the board seems in good shape, and the only loss was the RTC IC (UA2 on my board) since it's leads fell off, and what I presume are the two FETs to charge the lithium battery. Both have been removed from the board. The entire area around the 68000 and VIA check out just fine if I follow them according to the schematics.
However, when powering it up I get a screen with random artifacts on it, and a low pitch loud beep from it's speaker after a few seconds. It then sounds like it attempts to read the floppy, then stops after a few seconds. 10 seconds later this repeats with another beep, and more floppy noise.
I can't really find anything describing what this low pitch chime might be. Not sure if it's actually intentional or some fault on the board still. Does anyone know what it means? Is it an error code?
Video of the bootup + sounds: https://photos.app.goo.gl/kyN9d6Rxwcb1Vb5V7
As well, had a few questions on replacement parts as well -
I've since repaired it's power supply (4.95v for 5V supply, 11.82 for 12V supply), cleaned up the board, replaced all caps, and have been trying to get it to boot. Despite the battery leakage, the board seems in good shape, and the only loss was the RTC IC (UA2 on my board) since it's leads fell off, and what I presume are the two FETs to charge the lithium battery. Both have been removed from the board. The entire area around the 68000 and VIA check out just fine if I follow them according to the schematics.
However, when powering it up I get a screen with random artifacts on it, and a low pitch loud beep from it's speaker after a few seconds. It then sounds like it attempts to read the floppy, then stops after a few seconds. 10 seconds later this repeats with another beep, and more floppy noise.
I can't really find anything describing what this low pitch chime might be. Not sure if it's actually intentional or some fault on the board still. Does anyone know what it means? Is it an error code?
Video of the bootup + sounds: https://photos.app.goo.gl/kyN9d6Rxwcb1Vb5V7
As well, had a few questions on replacement parts as well -
- Can the Classic boot without it's RTC IC (UA2 on the board)? As mentioned, I pulled it from the board due to corrosion.
- Can the Classic boot without it's ROM (UE1 on the board)? I have a 40-pin ROM and the board has a 42-pin socket. During repairs I had the ROM off by one pin and it got quite toasty, so I presume it's dead. If I pull it, the screen produces rectangles on the screen with no beeps, with it the screen is totally garbled but it does chime.
- What is the PCB finger connector at the bottom of the board for? Not too relevant, just curious. My schematic doesn't mention what it's for.
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