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Commodore 1541-II Floppy Drive Repair

I was able to repair my Commodore 1541-II floppy drive, which is typically used together with the Commodore 64.

The first problem was that I do not have the original (external) power supply, but fortunately it uses fairly standard +5V and +12V voltages, which are also used by most PC hardware. So I made an adapter from a 4-pin molex to a 4-pin DIN connector:

Commodore 1541-II Power Adapter

The pinout of the DIN connector can be found here among other places.

When powering up the drive for the first time, it would keep the drive motor running constantly, which is apparently a known problem. Some other people online said this could be caused by a faulty PSU or bad ROM chip...

When I attempted to continue troubleshooting the next day, the situation had worsened. Now the power LED on the drive would flash a little on power on and slowly fade away. Symptoms of a short circuit or something perhaps...

With no idea on what to do about this, I decided to try to replace the electrolytic capacitors, which people often do on restoration/repair projects.

There are only three of them on the main board, all 10uF and 25V, located here:

Commodore 1541-II Capacitor Locations


Old and new replacements:

Commodore 1541-II Capacitor Replacement


To my surprise, this actually worked, and the drive is now working:

Commodore 1541-II Working


I have a theory: Two of those capacitors I changed are between the incoming 12V/5V and ground, acting as "decouping/bypass" to filter out noise. If there happened to be a short circuit or weakened resistance in the capacitors, that would explain parts of the symptoms at least.

Topic: Repair, by Kjetil @ 26/10-2019, Article Link