TEC FD-50x drives - known issues?

Dave Dunfield dave04a at dunfield.com
Sat Oct 8 20:51:56 CDT 2005

>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 :-)

>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.

>A drive exerciser is handy for this, but by no means essential.

Imagedisk's "Align/Test" function lets me excercise the drive with a fair
bit of manual control.

>You can 
>often get away with just pulling pins on the interface connector low with 
>bits of wire connected to the 0V line. And look at the outputs with a 
>logic probe. Remembr there output drivers are open-collector, so you need 
>to add terminating/pullup resistors (traditionally 150 ohms to +5V) for 
>Note that some drives with a big ASIC or microcontroller on them do some 
>kind of power-on initialisation. In particular, a few drives do odd 
>things if inputs are held active (low) at power-on. Other drives will 
>ignore all inputs if the power-on seek-to-track-0 fails. 
>If you have one of the latter units, you should be able to see 
>transitions on the stepper motor drive outputs just after power-on. And 
>you can check the track0 sensor by hand, of course.

All of this works.

>I can't believe it would be that hard to trace out a schematic. Even if 
>there's a big ASIC in the middle of the board (likely on half-height 
>drives), you can often figure out what it's doing from the surrounding 
>circuitry. You can at least check if things like senosr inputs do the 
>right things as you move a bit of card in and out of the sensor, etc.

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 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.


dave04a (at)    Dave Dunfield
dunfield (dot)  Firmware development services & tools: www.dunfield.com
com             Collector of vintage computing equipment:

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