Atari 1050 diskette drive repair

[Curtis H. Wilbar Jr.]

Steven Hirsch wrote:
> Anyone have experience with these?  I have a defective unit (purchased 
> on eBay - sad story) that tries to bash the drive head to death 
> against the Track 0 stop when turned on.  I picked up the service 
> manual and schematics and was able to verify that the Track 0 sensor 
> was working and that that NTRACK00 (pin 34) on the 2793 FDC chip is 
> pulled high at that point.
>
> It looks like the head-step pulses are generated in software by the 
> onboard 6507 CPU.  The four phases appear on PB2-5 of a 6532 IO 
> interface and are presumably getting cycled in the correct sequence 
> since the head moves quite smoothly until it hits the physical stop.
>
> I've already verified supply voltages and inspected the board closely 
> for burn marks, broken traces, etc. and reseated all the socketed ICs.
>
> The unit is fitted with the 'US Doubler' enhancement, about which I 
> know very little.

I don't know what the problem with your drive could be... you've already 
looked
at the first thing I'd have looked at (track 0 sensor).

As for the US Doubler, I have one of those (installed it into my 1050 
drive years
ago).  This is a drive software change to give true double density to 
the drives and
was originally used with SpartaDOS, but later I believe Dos 2.5 supports it.

It also has a high speed mode (which may only work for double density, I 
don't
recall at this point).

-- Curt

>
>
> Would appreciate any tips on troubleshooting.
>
>
> Steve
>
>
>