TEC FD-50x drives - known issues?

[Tony Duell]

> 
> >A disk drive performs several different functions. In particular, it 
> >rotates the disk, it detects the index hole and write protect notch, it 
> >moves the heads between cylinders and detects the track0 position, and it 
> >actually does the reading and writing.
> 
> This much I actually know :-)

One of the problems with this list is that it's impossible to know the 
knowledge/skill level of the person asking the question. 

Your original question did seem to suggest you thoguth of the floppy 
drive as a single unit, whereas as we both know, it's a collection of 
several systems. It certainly helps if we both know which of those 
systems is the problem.

> 
> 
> >Do you know which, if any, of these systems are working? Can you get the 
> >disk to spin? Do you get an index pulse? Can you get the head to move? 
> >And so on.
> 
> All functions appear to work (Motor, Index, Step) - problem in all cases
> is in the read/write circuitry. Drive goes through all the motions, it
> just can't read/write.

Ah, right (or is that Ah... Write :-)). Can you identify the read 
amplifier chain (often using NE592 ICs), or is it hidden in an ASIC.

In the latter case, look for a pair of LC filter networks connected to 
the ASIC. The read chain almost always consists of differential 
amplifiers right up to the final comparator stage, so you expect filters 
to come in pairs, etc. If you can find a pair of test point pins 
associated with those, then they're almost certainly the outputs you'd 
use for head alignemt. Hook a 'scope with differential inputs to those, 
try reading a normal disk (never put an alignment disk into a dodgy 
drive!). Do the signals look at all sane?

> It may come to this - At least I do have a couple of working drives
> that I can compare signals with - but I asked in case a) someone has
> the technical documentation or b) someone might say "oh yeah, thats
> a common problem caused by xxx...", either of which could save me a
> lot of time.

I don't know how complicated these drives are, but I can't believe it 
would tkae more than a day to figure out the read amplifier section, even 
if it is hidden in the ASIC. Sometimes it's quicker to just sit down and 
have a go :-)

> 
> I think I agree with Allison however that these drives are crap, and
> I'm not sure I want to spend a lot of time on them if suitable
> substitutes can be found - in this case, the physical constraints make
> this a but more challenging.

Well, I like to keep my machines as close to original as possible.

-tony