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" <a...@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 >
