68kMLA Classic Interface
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| Performa 450 restore / no chime | |
| Posted by: c00gr on 2023-08-08 22:35:32 Hey folks… picked up a Performa 450 at an estate sale and the board was a bit grungy with leaky caps, but otherwise in decent cosmetic condition. PSU voltage looks good, fan spins, HD spins up, but then no chime, and then the HD idles. Recapped the board as well, checked traces around the caps and things seem ok except for the negative side of C13 where a soldered in a jumper to the back of the board. I recorded a video of where I’m at currently, but not sure where to go from here… open to any ideas you might have! Here’s the video: | |
| Posted by: joshc on 2023-08-08 23:35:34 Apologies I haven’t watched the video but what voltages is the power supply outputting? | |
| Posted by: volvo242gt on 2023-08-08 23:38:24 Guess there's someone over at the other forums having similar issues: https://tinkerdifferent.com/threads/macintosh-lciii-start-up-failure.2863/ -J | |
Posted by: c00gr on 2023-08-09 00:44:37Apologies I haven’t watched the video but what voltages is the power supply outputting?5, 12, -5 as expected from the PSU. Didn’t probe in other locations though… | |
| Posted by: joshc on 2023-08-09 00:45:38 Potentially a bad Egret chip. Have you got any photos of your board so I can see if I can spot anything? | |
| Posted by: c00gr on 2023-08-09 10:00:21 Here are some photos of the board… I’ve been checking traces on the EGRET chip and so far things seem continuous, but I still need to trace a few more pins… | |
| Posted by: Phipli on 2023-08-09 10:52:26 Was it the LC III that has the incorrect silkscreen on one of the caps? Like, the -12 supply cap silkscreen was backwards? | |
Posted by: c00gr on 2023-08-09 11:17:10Was it the LC III that has the incorrect silkscreen on one of the caps? Like, the -12 supply cap silkscreen was backwards?Yup, saw that too… I reversed C22 and so far didn’t change anything. | |
| Posted by: c00gr on 2023-08-09 13:51:58 Also reflowed the EGRET chip and still nothing. Also checked voltage on pin 4 of U22 and it’s 4.9V… | |
| Posted by: c00gr on 2023-08-09 13:52:53 I wonder if the ROM chips are bad… Any ideas on how to check them? I have an EPROM reader so I guess I could try to see what’s there? | |
| Posted by: c00gr on 2023-08-09 14:25:38 Also I checked voltage on U7 Pin 15 and it was 0.1… is that expected? Confused a bit about the refresh circuit… | |
| Posted by: joshc on 2023-08-10 06:19:52 I can see some top layer corrosion on the PCB near the DFAC/Sound Chip, around some of the vias there:  The DFAC is part of the Reset circuit, definitely worth checking continuity of everything around there and check if those vias are compromised. | |
| Posted by: c00gr on 2023-08-10 08:01:00 Traces on the side of U1 with the corrosion all check out and the vias as well… | |
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