Trying to fix my first 1541 which I got off eBay.
Turning the 1541 on while not connected to the C64, the green LED comes on then the red LED and after 2 seconds it turns off. The spindle however keeps on spinning. Also no moment on the head.
Checked the 12V and 5V. Both stable, no ripple. 11.9V and 4.9V on both lines.
Reset line is fine, swapped out 6502 and 6522 with working chips on my Vic-20. No luck.
Checked 1MHZ clock from the oscillator. All good.
Re-seated all chips (6502, 6522, roms)
If I connect the 1541 to the C64, turn the 1541 and then turn on the C64 the red LED pulses again so the reset seems good.
Running the load “$”,8 on the C64 just hangs. With the 1541 turned off the load command at least fails with device not found so it looks like it’s picking it up.
Thought it might be a faulty ROM so built a 28 to 24 pin converter using the guide from http://ist.uwaterloo.ca/~schepers/sockets.html
Tried replacing both the UB3 and UB4 DOS/Kernel, no luck.
Then got out the logic analyser and found gates blown on both the 7417 and 7406. After replacing those the spindle stopped with its constant spinning and disks then loaded up perfectly.
A useful troubleshooting guide from Ray Carlsen:
To aid in my troubleshooting I’ve taken the pdf schematic which is not very clear and converted to KiCAD and uploaded to https://www.baldengineer.com/bit-preserve-vintage-schematics-with-kicad.html