Commodore SX64 probs...

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Sun Jul 18 19:58:45 2004

> 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