The 1541 Floppy Drive for the Commodore 64 connects to the C64 via the Serial port.

There as several versions. Some power on with just mains, and others use a custom adapter like the 1541-II.

The power supply is specific to the 1541 and not the same as the C64 power.

The 5V rail is rated at 700mA and pulls 400mA.

The 12V rail is rated at 500mA and pulls 500mA, so really wants to be 1A.

A simple test if the head is good is to disconnect the wire that goes to the magnetic pickup head and test all the wires (usually 4) with continuity between themselves. So put your meter into resistance mode, one probe on a wire, then touch over the other 3 wires one at a time.

As you do, you should see a reading around 4 to 20ohm typically. Open circuit or over 100 ohm is considered bad and basically not fixable.

The floppy disk has a ROM onboardd that can be removed, read in using an EEPROM reader, or replaced with a new one to check it is good.

The 1541 with Board Rev. 154008, 154050, 250442, 250446 (old 1541 case) has the Rom 901229 (DOS Hi-Rom) and can be replaced with 27C64 (8KB).

The 1541-C with Board Rev. short motherboard (sometimes old 1541 Board in a new White Case) has the Rom 251968 (DOS Low-Rom & DOS High-Rom) and can be replaced with 27C128 (16KB).

The 1541-II has Rom 251968 (DOS Low-Rom & DOS High-Rom) and can be replaced with 27C128 (16KB).

If using an XgPro EEPROM Reader like the T56, select any IC with 2764 or 27128 depending on your version, and make sure to uncheck "Pin Detect" and "Check ID". Then read, save to file and you can compare to known working dumps.

To test the VIA chips (MOS 6522) it is best to remove them and put them in a BackBit Tester.

This way you can socket them and also be sure 100% of the functions are working.

The CPU used is a MOS 6502. To test the 6502 CPU it is best to remove them and put them in a BackBit Tester.

This way you can socket them and also be sure 100% of the functions are working.

Alternatively probing the CPU for its !RESET lines, address, data and other pins for confirmed operation is also an option.

The Gate Array controls the motors for moving the head back and forth, as well as some other logic.

If you notice your head isn't moving or very little, it could be the gate array, it is fairly common.

To test the Gate Aray chip (MOS 251828) it is best to remove it and put it in a BackBit Tester.

This way you can socket it and also be sure 100% of the functions are working.