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Macintosh 128k No Chime and Strange Sounds. Need Help to Restore
Posted by: JoeD on 2020-06-25 21:16:48 I am the original owner of a 128k Mac from my first year at Drexel University in 1985. I am trying to restore it back to operating condition. When I powered it up I got the Chime and then the Sad Mac Icon with code 040820 was displayed with a good quality screen picture. So I replaced RAM chips G8 and F10. After that I powered it up and got the Chime and then the Sad Mac Icon with code 020040 was displayed, also with a good quality screen picture. So I replaced RAM chip F11. Now when I power it up I no longer get a chime, the screen comes on with basically a white/black static display, and I get random static sounds out of the speaker. See two links to videos of the current symptoms. Any idea what might have gone wrong with my second RAM chip replacement, or other ideas of what could be wrong now? https://youtu.be/Ia_2mJJljBY https://youtu.be/qqnZmm0ND_g
Posted by: bibilit on 2020-06-25 22:34:53 A broken trace somewhere ? i will have a look at continuity first between ram chips. Piggybacking can also help.
Posted by: JoeD on 2020-06-25 22:37:19 I rechecked pin to pin continuity with one probe on F5 and the other probe on the corresponding pin of F12. Went through all pins on both sides of the RAM and then repeated for row G. All pins checked out good with the exception of Pin 3 on one side and pin 2 on the other side of the RAM chip are not connected across the row for either row F or G. That seems to be normal. I also checked continuity between adjacent pins on F11 and there were no shorted pins. So unfortunately, the pin continuity through the traces on the PCB does not seem to be a problem. I also had another new RAM chip so i changed F11 with a different new RAM chip, but still have the same issue on power up.
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