fri0701
Well-known member
Hi everyone,
I recently got back into my Apple /// repair, and I've come to a point where I need some help.
I have the 5V RAM board, 256k model.
Earlier this year, I tested my power supply, and although the +12V line was stable, the +5V line was jumping all over the place. I replaced all the electrolytic and filter caps on the supply, as well as a faulty transistor.
The supply now is stable, and I measured these output voltages with no load:
For the +12V supply: +12.03V
For the +5V supply: +5.12V
For the -5V supply: -3.96V
For the -12V supply: -10.38V
Obviously, the -5V and -12V supplies are a bit low for comfort, but I don't know where to look next to fix this.
Also, now the supply powers on the computer, and the screen displays a flashing configuration of random characters. I've since recapped the RAM board and the main logic board, but nothing has changed. When I run the machine without a RAM board, the screen just displays all white. The LED on the main board lights up, as well as the keyboard light. The Control-Reset key combination still works as well.
I don't exactly know where to proceed from here. I've got a couple //e's here that I'd be happy to salvage parts from, if need be. I'm under the impression that they use the same RAM chips as well. Once, I tested all the RAM from the /// in my //e, and it all checked out fine (as far as I remember), but that was a while ago.
I've got a multimeter here that can check voltages, resistances, continuity, etc. Unfortunately, I don't have access to my scope at the moment.
Pictures of anything available upon request.
Thanks!
- fri0701
I recently got back into my Apple /// repair, and I've come to a point where I need some help.
I have the 5V RAM board, 256k model.
Earlier this year, I tested my power supply, and although the +12V line was stable, the +5V line was jumping all over the place. I replaced all the electrolytic and filter caps on the supply, as well as a faulty transistor.
The supply now is stable, and I measured these output voltages with no load:
For the +12V supply: +12.03V
For the +5V supply: +5.12V
For the -5V supply: -3.96V
For the -12V supply: -10.38V
Obviously, the -5V and -12V supplies are a bit low for comfort, but I don't know where to look next to fix this.
Also, now the supply powers on the computer, and the screen displays a flashing configuration of random characters. I've since recapped the RAM board and the main logic board, but nothing has changed. When I run the machine without a RAM board, the screen just displays all white. The LED on the main board lights up, as well as the keyboard light. The Control-Reset key combination still works as well.
I don't exactly know where to proceed from here. I've got a couple //e's here that I'd be happy to salvage parts from, if need be. I'm under the impression that they use the same RAM chips as well. Once, I tested all the RAM from the /// in my //e, and it all checked out fine (as far as I remember), but that was a while ago.
I've got a multimeter here that can check voltages, resistances, continuity, etc. Unfortunately, I don't have access to my scope at the moment.
Pictures of anything available upon request.
Thanks!
- fri0701
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