TM848 repair?

[Chuck Guzis]

On 7/13/20 11:18 AM, Jim Brain via cctalk wrote:
> Anyone on list repair or rehab Tandon TM848 drives?  I have a 4 or so of
> the slimline drives from some Tandy Model 12/16b units that don't seem
> to spin at all, and I've hooked them up to the same PSU that a TM848E
> successfully runs on, so I am guessing it's not a PSU issue. (Though, my
> understanding of 8" drives is extremely minimal, so...)
> 
> If I could get just 2 of them working, that'd put a few 12/16b units
> back in operation.

The Tandon 848 is not one of my favorite drives.  There is an option not
to pass the Motor On/ signal unless a disk is loaded and the drive door
is closed.  Check U16 pin 8, which should be high for MOTOR ON.

It seems more like an oversight that all 4 drives don't spin.  Be aware
that the 848's motor controls are different from 5.25", where one line
controls all motors.  The 848 uses pins 4,6,8 and 24 on the interface to
control the motor--each drive has a jumper that dictates which line will
be used. (MC 1-4).

--Chuck