Posted By
Hans
on 2012-07-15
07:52:55
|  Re: Getting a pair of 1551s
Hi Richard,
<quote>.....drive S/N 10754 wouldn't work at first; the +4 reported "device not found" and the drive gave a repeating 2-blink code on the red light. I tried to find a service manual for the 1551 but couldn't. I did find an old PET drive service manual claiming that a 2-blink code means DOS ROM error. I pulled the EPROMS out of both drives and found that the working drive had the correct eprom data (as tested via md5 hash with a ROM that I downloaded from the web) while the non-working drive had different eprom data. I took a spare 27C128 eprom and burned it with the correct dos eprom data......</quote>
That's mysterious. Your changing the AC power supply from 220 VAC (at 50 Hz) to 115 VAC at 60 Hz certainly has nothing to do with the cloag & dagger behaviour of the floppy's internal DC circuits (to which the eprom you are quoting belongs to), and I've never heard that an eprom would change its stored data unless it's exposed to UV radiation.
In my opinion this can only mean that the 1551 never has been operational before you fixed it with a rewritten eprom. Strange....
Regards,
Hans.
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