Osborne 1: Adapting for conventional Shugart with a TM-100-1?

[MissArgent]

So, my B: drive's suddenly stopped being able to actuate the head carriage at all in a way that seems to indicate a fault with a discrete component on the drive. While I haven't given up on it yet, I've had hacking together a crude adapter for a conventional shugart drive in mind if need calls for it as a last resort option - It looks like someone's already done the groundwork here, but they had Gotek use in mind. For a real FDD, It'd just be a matter of splicing a molex connector into the voltage out lines in lieu of just leaving them disconnected, wouldn't it?

 

[MissArgent]

ADDENDUM: Schematics for Osborne's custom logic board can be found here, p. 105 (129 by PDF numbering).

 

[Chuck(G)]

Basically, you cut the wires going to pins 11,13,15,17 and connect them to the +12 side of a 4-pin molex power connector and pins 21,23,25 and connect them to the +5 side. Get your ground from any of the other odd-numbered pins.

If that's what you're planning, it'll work.

 

[MissArgent]

Yup! That's what I had in mind.

As far as the current drive goes, tentative logic probing implicates a MC14023B on the offending board. Got a part order in and am hoping for the best...

 

[MissArgent]

Unfortunately, it wasn't the MC14023. The plot's also thickened. (Oh, I hate it when it does that.)

When I swapped the two drives' controller boards after realizing the 14023 swap didn't fix the bad drive's issues, neither Controller A (my known good drive's controller) in Drive B nor Controller B (the board with the 14023 i just replaced) in Drive A worked. The A/B pair exhibited the same symptoms normally seen in the B/B pair, while the B/A pair just kept "jittering" the head back and forth repeatedly. Clearly, B: has both mechanical and logic board-related issues...It's been one of those days.

So, once I've got my PC 5150 and XT's drive issues sorted out I think I will consider swapping in my spare TM-100-1A with a hacked up cable adapter. Non-connect some pins, patch out the +5V, +12VDC, and two ground wires into a molex connection...Dead simple. Hopefully. Weirdly, CMI and Tandon used the same bezel design so the faceplate shouldn't cause any issues here.