> I've stripped one machine down. It has three main boards, labelled as
> CPU, floppy drive controller, and I/O.
>
> Prominent ICs on the CPU board (all MOS apart from the EPROM):
>
> 6510 / CBM (40 pins)
CPU
> 6569R3 (40 pins)
Video, I guess
> 906114-01 (28 pins)
ROM? PLA? (IIRC the 82S100 does have 28 pins)
> 901226-01 (24 pins)
ROM?
> 6581 (28 pins)
Sound
> 901225-01 (24 pins)
> 2564 EPROM
>
> Prominent ICs on the FDC controller board (again, all MOS apart from RAM
> / ROM):
>
> 6502 (40 pins)
CPU
> 6522 x 2 (40 pins)
VIA (I/O chips)
> 325572-01 (40 pins)
Disk inteface (shift register, encoder/decode, etc)
> 325302-01 (24 pins)
ROM, maybe???
> 2564 EPROM
> 2116 RAM
>
> .. plus the I/O board has a pair of MOS 6526 40-pin ICs.
CIA I/O chips I think.
>
> The reset from the switch on the front of the machine hooks into the FDC
> board and appears to reset the 6502 there, which then must in turn reset
> whichever is the CPU on the CPU board...
Or maybe there's a common reset line for the 2 CPUs, and the reset
circuit happens to be on the FDC card. Have you tried checking clock and
reset lines with a logic probe?
> There's no output at all from the supply on the +5V or +12V lines, but
> the output from the bridge rectifier within the first parts of the PSU
> circuit are giving a good DC reading, so it's not something simple.
OK.
>
> These PSU's have a pair of little sub-PCB modules mounted on them, one
> for 5V and one for 12V, each with an MB3759 IC on them - however as I'm
IIRC, that's similar to a very common switching regulator chip (78S40 or
something?)
> getting nothing on either power rail it suggests the fault's elsewhere
> in the PSU.
Is there anything, other than power inputs, that's common to the 2
regulator modules?
I assuem there's nothing useful on ftp.funet.fi?
-tony
Received on Sun Jul 18 2004 - 19:58:45 BST
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