Atari 1050 diskette drive repair

[Steven Hirsch]

On Thu, 22 May 2008, 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.
>
> Would appreciate any tips on troubleshooting.

During the recent list latency (what happened, anyway?) I tracked the 
problem to a defective WD2793 FDC chip.  These appear to be just about 
pure unobtanium, however.  Besides eBay, does anyone know of a source for 
onsie-twosies?

While we're on that subject, I would love to know how to search for items 
like this on Google without wading through dozens and dozens of these 
obnoxious "Submit your RFQ here and we'll respond" sites.  Most of them 
seem rather fly-by-night, and none of them will deal in small quantities.

Steve


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