Some tips from cctalk describing Tandon TM-848 8" disk maintanance or repair:
"...>> Start by checking the 24V > 12V regulator...
> Second that! I've had to replace more than one regulator on 848s; also
> the 100 ohm resistor (R1) and electrolytic capacitor(C6) on the input
> side of the regulator. ..."