Hello!
I bought a Mac 512 that has a problem with the mainboard. When I got the Mac, the ROM chips (low, high) were interchanged and the MAC did not start. I changed the ROM chips and the the MAC started somtimes. Sometimes I got a sad MAC with the error 05FFFF. Sometimes I got no Image and sometime the MAC started up to the disk picture. At every start I do not get a chime. When I put in a disk the picture begins to wooble and then the MAC crashes, sometime there can be heard some sounds. I can not read a disk without crashing.
What I did up to now:
- Changed the ROM against a ROM from as Plus => mainboard did not start (I tried this only one time, so I do not know if the mac would start, when I try it more often)
- Changed the whole mainboard against a Plus mainboard => computer starts (analog board seems to be ok).
- Controlled the voltages: +5, +12 and -12 are ok!
- resoldered the mainboard connector from the analog board
- changed the electrolytic capacitors. One of the capacitors (33mF, C5) could not be measured when it is soldered. Before soldering it shows 33mF after soldering it was not possible to measure. The other two could be measured when they were soldered. The polarity of all capacitors is correct.
I do not have another diskdrive, so I could not test, if the drive is the problem, but I think there must be a problem on the mainboard. There is no chime, starting did not work every time (sometimes no picture, sometime sad mac, sometimes "disk mac"). If I do not connect the disk drive the problem occurs too.
When I opened the Mac I saw that that the shield of the mainboard (metal sheet under the mainboard) had no paper card on the mainboard side, there was no isolation! So I think that there could been a short on the mainboard caused by the shield.
Ok, I hope you can understand, what I wrote. I am from Germany...
Has anybody an idea what I can do to repair the mainboard? It would be very nice to see this machine working again.
Greetings
Martin
I bought a Mac 512 that has a problem with the mainboard. When I got the Mac, the ROM chips (low, high) were interchanged and the MAC did not start. I changed the ROM chips and the the MAC started somtimes. Sometimes I got a sad MAC with the error 05FFFF. Sometimes I got no Image and sometime the MAC started up to the disk picture. At every start I do not get a chime. When I put in a disk the picture begins to wooble and then the MAC crashes, sometime there can be heard some sounds. I can not read a disk without crashing.
What I did up to now:
- Changed the ROM against a ROM from as Plus => mainboard did not start (I tried this only one time, so I do not know if the mac would start, when I try it more often)
- Changed the whole mainboard against a Plus mainboard => computer starts (analog board seems to be ok).
- Controlled the voltages: +5, +12 and -12 are ok!
- resoldered the mainboard connector from the analog board
- changed the electrolytic capacitors. One of the capacitors (33mF, C5) could not be measured when it is soldered. Before soldering it shows 33mF after soldering it was not possible to measure. The other two could be measured when they were soldered. The polarity of all capacitors is correct.
I do not have another diskdrive, so I could not test, if the drive is the problem, but I think there must be a problem on the mainboard. There is no chime, starting did not work every time (sometimes no picture, sometime sad mac, sometimes "disk mac"). If I do not connect the disk drive the problem occurs too.
When I opened the Mac I saw that that the shield of the mainboard (metal sheet under the mainboard) had no paper card on the mainboard side, there was no isolation! So I think that there could been a short on the mainboard caused by the shield.
Ok, I hope you can understand, what I wrote. I am from Germany...
Has anybody an idea what I can do to repair the mainboard? It would be very nice to see this machine working again.
Greetings
Martin
