CBM 1541 drive faults

Alexandre Souza alexandre.tabajara at gmail.com
Sun Dec 13 12:42:35 CST 2015

Had lots of 6522 and ROM failures here. I'd begin with rom replacement

Enviado do meu Tele-Movel
Em 13/12/2015 16:34, "tony duell" <ard at p850ug1.demon.co.uk> escreveu:

> >
> > Yes, I've certainly seen that on the schematics, and was considering them
> > as a likely failure too - after opening cases though, my drives all seem
> to
> > have a single larger SRAM (even the Rev A board, so that's presumably
> "Rev
> > A of the type that doesn't use 2114's" :-)
> Yes, later versions used a single 6116 RAM (which as you said is not likely
> to be the problem).
> I have had a ROM failure in a 1541. I am pretty sure mine now has an EPROM
> in a home-made kludgeboard (to move the enables round, etc) in it.
> I think at this point you have to do real tests, there is no stock fault.
> I do
> have the Sams book on the 1541 somewhere, but IIIRC it suggests swapping
> out the socketed devices (ROMs, RAM(s), VIA, CPU, etc. If that doesn't help
> then you pull the CPU and force the logic levels of the address pins to
> check
> the address decoder circuitry (but the address decoder almost never fails).
> I am pretty sure the firmware is not changed for different PCBs. I would
> keep
> ROMs in pairs just in case there is a different revision and it matters,
> but I think
> you could put the ROMs from the defective drive into a good one and see
> what
> the LED does.
> -tony

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