Atari 1050 diskette drive repair

Steven Hirsch snhirsch at gmail.com
Thu May 22 06:56:27 CDT 2008


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.


Steve



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