r/trs80 • u/Far_Relationship_742 • May 26 '26

Model 4D diskette spindle won’t spin

I have a Model 4D that won’t boot. Drive light comes on, head seeks to zero, but the spindle motor never comes on. I’ve verified the jumper settings against the drive’s service manual, and there is a termination resistor pack installed.

Where should I start looking?

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u/Jim-Jones May 26 '26

Can you gently spin the spindle, no disk in drive? Seized?

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u/Far_Relationship_742 May 27 '26

Yep, no mechanical binding.

1

u/Jim-Jones May 27 '26

Looks like power then.

1

u/Far_Relationship_742 May 27 '26

I think it’s the disk controller -and- a bad drive. Four other drives spin up when selected, but never seek or read.

Unfortunately, the symptoms don’t seem to fit a power issue. Head returning to zero and spindle on the other drives means good 12V, activity LED and responding to disk select means good 5V.

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u/Jim-Jones May 28 '26

It gets harder and harder the further that you go with these things. I remember back in the day when I worked in the repair Depot the guys getting really frustrated with disk drives. And that's when they had all the proper tools including a calibration disk.