18 Jul
2004
18 Jul
'04
12:58 p.m.
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