all,
Hope I can get some help from the group.
I am debugging a Drive ][ I have where the spindle appears to the running at about half speed.
I haver verified that
the belt is not slipping
the spindle (big flywheel) spins freely withe belt removed
the motor spins freely when not powered
Adjusting VR1 (to both end points) changes the speed, but never lets me the speed correct (not even close)
So starting thinking electrical, looking at pin 7 of the speed control chip the voltage was reading kind of low like 10.5 volts vs 11.8 and the motor seemed to not have alot of torque.
I had a spare speed control chip and swapped that out but with no change in performance.
So I am about to start really digging and tracing through the whole speed control board, but thought I would ask if anybody had any advice first.
Thanks
Check the following:
- that your power supply is truly outputting +12V
- that those 12V are reaching the disk drive
- that the spindle motor is turning freely - a single drop of light machine oil (like 3-in-1) on the spindle motor shaft at both ends works wonders sometimes.
- that the drive chuck is turning freely - same comment on lube
Next check the electrolytic capacitor on the speed board, and the switching transistor, an X45C683 (obsolete, of course, and no datasheet that I can find). That is, if your drive is Shugart based. Also, you touched on the speed control IC. If it is a DIP 14 then it's for a Shugart. If it is a SIP package, it's an Alps.
If your drive is Alps based then some of the speed control comments may need to be modified. However, if it's an Alps based mechanism, you can cannibalize a Commodore 1541 drive - they also use standard APLS mechanisms with identical speed control circuitry.