Re: Two 1541-II drives with problems

On 19 April 2014 14:14:23 CEST, Ville Laustela <ville.laustela@gmail.com> wrote:

>- power on: normal activity (power led on, spindle runs and drive led
>lights for few seconds, then stop)

That's good. Means that it found no internal problems. The worst usually is when the led remains on all the time

>- connected to a C64: drive resets with the computer normally

You mean when you power the computer on? There goes a RESET line along the cable. If the drive passes its POST at power up, you can quite safely bet that it will pass the reset correctly as well. At least I haven't seen a single case that would not. 

>- attempting to load halts at "SEARCHING FOR": drive spins (with leds
>on) but the stepper doesn't move. Only way out is to reset the
>computer.

Which tells us that the communication from the computer to the drive works more or less fine (drive received expected commands and tries to deliver results). The problem looks like the communication back doesn't work. This would indeed point to the ICs mentioned below. 

>
>By the Ray Carlsen's website
>(http://personalpages.tds.net/~rcarlsen/cbm/1541/1541-II/1541-II.txt)
>these symptoms point to either U7 logic chip (7406) or U6 VIA (6522).
>On one of the two drives I replaced the U7 chip but that had no effect.
>
>Before I start a (lenghty, painful, boring...) removal of the 6522 VIA,
>I would like to ask here if anyone would have any other ideas?

If you have a way to check the serial lines with a scope that should shed more light. But.. manage your expectations and be prepared for the boring job anyway. While one can never be 100% sure, odds are good that new VIA is your friend there. 

-- 
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