Tandon TM848-2 Floppy drive power
ard at p850ug1.demon.co.uk
Fri Jan 26 17:15:21 CST 2007
> > > 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.
> Now you've got me. I didn't look at it from this point of view. There
> is no trace for it. Period, doesn't exist at all. Of course we all know
> that published schematics are all 100% correct (this is a dig at
> schematics in general, not you Tony). There isn't even a land for it on
I am well aware of that. The scehmatic for the Tandy Model 3 PSU in the
technical manual not only has little in common with the actual supply
PCB, it's not even a possible schematic of a working SMPSU!
> the circuit board on the drive I'm looking at. Physically, there are 5
> black wires coming from the AMP plug to the circuit board. Pin 4 isn't
> poulated and there's no open land on the board.
You see, how _I_ see it is as follows :
There is a de-facto standard for power cables to 8" floppy drives, which
includes a +12V supply on pin 4. Tandy used this wiring in their Model
6000 (or whatever the machine is), so that just about any 8" drives could
The Tandon drive they actually fitted doesn't use an external +12V
supply. Pin 4 is not fitted at all, so you can plug in a power harness
with a +12V supply on pin 4 if you want to, and there'd be no problems.
Now what would have been _very_ foolish would be if Tandy had put
something other than N/C or +12V on pin 4 of that connector. Or if Tandon
had fitted pin 4 and connected it to something other than a 12V power
input. But from what you've told me neither of these are the case.
More information about the cctech