LC / LCII / LCIII / Q605 - Dyna Comp DCF 353 Power Supply Woes

[dougg3]

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:

 

[MiCv2]

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.

 

[coisasdavida]

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!

 

[MBehr]

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.