Tandon TM848-2 Floppy drive power

[Tony Duell]

> I'm glad your not working on projects for me then. Having potentially 
> damaging voltage on a connector that is not needed doesn't sound like 
> good practices to me. 

I don't see it like that at all...

I think Tandy were wiring the harness so any normal 8" drive sould be 
used. Some drives needed the 12V, some produced it internally from the 
24V line, so Tandy provided it on the cable for those drives that need it.

It's like PC floppy drives. Every PC I've ever worked on has 4 pin floppy 
drive power connecotrs : +_5V, +12V, and a couple of grounds. Most 
modern-ish 3.5" drives use 5V only. Are you saying that PC power supplies 
shouldn't connect up the 12V pin

> 
> I have the service manual here for this drive. No where does it say 
> that pin 4 is not connected to anything. Nor do the schematics I have 
> show that this drive's 7812 (which is how it is referenced in the print) 
> is optional. The only source for +12 on this schematic is the 7812, 
> derrived from the +24v line on Pin 1. 

Sure. That drive produces its 12V rail internally.

Since you have the schematics, can you tell me what pin 4 _is_ shown as 
being connected to, please.

> 
> Tandy also uses the same connector on the same power supply wiring 
> harness, but with a completely different pinout (and using the same 
> color scheme in some instances) to provide power to the card cage riser 
> IN THE SAME MACHINE. If you use this connector on the drive instead of 
> the riser, bad things happen. If you use the drive power connector on 
> the riser, bad things happen. The only way to tell them apart reliably 
> is that the drive power cable has two connectors (to power 2 drives) and 
> the riser power connector has only one AMP connector.

I rememebr one of the old Sun machines (Sun 2?) that used an Archive 
Sidewinder QIC drive. It has a 4 pin power connector, jsut like the one 
on a 5.25" drive. There's only one problem. The Sidewinder uses +5V and 
+24V.  And IIRC the only differnce in the tape drive pwoer connector was 
the colour of thew wire to one pin.

-tony