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LC / LCII / LCIII / Q605 - Dyna Comp DCF 353 Power Supply Woes
Posted by: dougg3 on 2026-01-12 15:42:44 I've seen other pictures online where R25 was missing, but the leads were soldered in. Other pictures show R25 installed, but its value isn't visible. I can't easily open mine up to provide more detail right now, but here's a picture I took while I was repairing it at the end of 2024. I always have trouble with the bands. Sometimes it's hard to tell brown and violet apart, and I never know what side to start on. I hope this is useful:
Posted by: MiCv2 on 2026-01-12 22:19:29 Thank you for the image; I'll try to determine the value based on the color coding. It's a shame there's no circuit diagram for it.
Posted by: coisasdavida on 2026-02-03 01:43:05 Recently given to me was a Performa 450/ LC III plus a Performa Monitor. Performa is completely dead. I removed the PRAM battery. Tried to simulate a charged one and shorted pins 2 and 4 on the ADB port, nothing. Unplugged floppy, HD, same. Checked PSU and I measure no voltage on it from any of the colored wires. It is a Dyna Corp PSU. I check board and inside PSU, no blown caps, no caps with powdery or liquid residue. Found this post. Replaced C9 --> joy!
Posted by: MBehr on 2026-02-03 03:42:21 Recently given to me was a Performa 450/ LC III plus a Performa Monitor. Performa is completely dead. I removed the PRAM battery. Tried to simulate a charged one and shorted pins 2 and 4 on the ADB port, nothing. Unplugged floppy, HD, same. Checked PSU and I measure no voltage on it from any of the colored wires. It is a Dyna Corp PSU. I check board and inside PSU, no blown caps, no caps with powdery or liquid residue. Found this post. Replaced C9 --> joy! Sounds great, congratulations! I wonder how a capacitor like C9 can fail without any external signs, like burning or leaking, but apparently it can. I also find it difficult to diagnose capacitors while they are still attached - of course the measurement is affected by the rest of the circuit. Maybe there are some special techniques for that. So a rule of thumb like "replace C9 in a dead Dyna power supply" is very useful.
Posted by: coisasdavida on 2026-02-03 04:41:59 Sounds great, congratulations! I wonder how a capacitor like C9 can fail without any external signs, like burning or leaking, but apparently it can. I also find it difficult to diagnose capacitors while they are still attached - of course the measurement is affected by the rest of the circuit. Maybe there are some special techniques for that. So a rule of thumb like "replace C9 in a dead Dyna power supply" is very useful. After removing it, I could feel it being a bit oily, but who knows.
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