17 Jul
2004
17 Jul
'04
9:15 a.m.
I've got a pair of non-working Commodore SX64's here.
One machine powers up, but the floppy drive light remains lit and I can
hear the drive spinning continuously, and there's a 50% grey pattern
filling the screen (i.e. pixels look to be alternating white/black).
Actually, there's also short run of pixels middle-bottom of the screen
which aren't illuminated at all. Pressing reset has no effect. Pressing
caps-lock does result in the caps-lock light illuminating, but I don't
know if that's a simple circuit hardwired to the key and doesn't go via
the CPU...
The second machine is totally dead - no activity whatsoever. There's a
*very faint* humming noise from the monitor area, typical of a display
that's at least getting power though - but on the CPU side of things no
chips seem to be getting remotely warm, suggesting that there's no +5V.
Before I start digging deeper, does the fault with the first machine
sound familiar, and are there any common PSU faults which affect these
systems? Plus, anyone have schematics they could scan?
Be nice to get one of them going. One keyboard is damaged (plus I only
have the one original keyboard cable), so it's only really viable to
have one running, but I'd like to get to the bottom of what's up with
both of them...
cheers,
Jules
17 Jul
17 Jul
10:28 a.m.
I've got a pair of non-working Commodore SX64's here.
One machine powers up, but the floppy drive light remains lit and I can
hear the drive spinning continuously, and there's a 50% grey pattern
filling the screen (i.e. pixels look to be alternating white/black).
Actually, there's also short run of pixels middle-bottom of the screen
which aren't illuminated at all. Pressing reset has no effect. Pressing
caps-lock does result in the caps-lock light illuminating, but I don't
know if that's a simple circuit hardwired to the key and doesn't go via
the CPU...
Is this thing like a C64 + 1541 drive? In other words, does the disk
drive have its own 6502 CPU? If so, then you either have 2 faults, or a
fault in what little circuitry is common to both of them.
I would start by checking the PSUs (voltage and ripple). CBM machines of
this vintage suffer from bad IC sockets, so it's worth at least
re-seating all socketed chips, and maybe replacing the sockets (with
turned-pin ones).
Can the main CPU hold the disk CPU in a reset state? If so, then maybe
the LED and motor-on lines are asserted. Maybe the main CPU is not
initialising the serial bus correctly, and you only have a fault in that
area (RAM, ROM, is there an 82S100 PLA in this machine?)
The second machine is totally dead - no activity whatsoever. There's a
*very faint* humming noise from the monitor area, typical of a display
that's at least getting power though - but on the CPU side of things no
chips seem to be getting remotely warm, suggesting that there's no +5V.
A voltmeter will verify the truth of that last statement, but alas the
voltmeter that does tests over the internet has yet to be invented :-).
It'll be a lot quicker if you do said simple test(s) before I start
thinking of possible causes.
-tony
18 Jul
18 Jul
8:39 a.m.
On Sat, 2004-07-17 at 22:28, Tony Duell wrote:
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)
6569R3 (40 pins)
906114-01 (28 pins)
901226-01 (24 pins)
6581 (28 pins)
901225-01 (24 pins)
2564 EPROM
Prominent ICs on the FDC controller board (again, all MOS apart from RAM
/ ROM):
6502 (40 pins)
6522 x 2 (40 pins)
325572-01 (40 pins)
325302-01 (24 pins)
2564 EPROM
2116 RAM
.. plus the I/O board has a pair of MOS 6526 40-pin ICs.
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...
:-)
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.
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
getting nothing on either power rail it suggests the fault's elsewhere
in the PSU.
Leave that one with me, as I've at least got the other PSU which works
and I can take readings from. I was hoping that someone would come
forward with schematics, or that there was a known failure point with
the supplies in these machines.
cheers
Jules
I've got a pair of non-working Commodore SX64's here.
One machine powers up, but the floppy drive light remains lit and I can
hear the drive spinning continuously, and there's a 50% grey pattern
filling the screen (i.e. pixels look to be alternating white/black).
Actually, there's also short run of pixels middle-bottom of the screen
which aren't illuminated at all. Pressing reset has no effect. Pressing
caps-lock does result in the caps-lock light illuminating, but I don't
know if that's a simple circuit hardwired to the key and doesn't go via
the CPU...
Is this thing like a C64 + 1541 drive? In other words, does the disk
drive have its own 6502 CPU? If so, then you either have 2 faults, or a
fault in what little circuitry is common to both of them. Can the main CPU hold the disk CPU in a reset state?
If so, then maybe
the LED and motor-on lines are asserted. Maybe the main CPU is not
initialising the serial bus correctly, and you only have a fault in that
area (RAM, ROM, is there an 82S100 PLA in this machine?)
I've read elsewhere that PLA chips in C64's die often and randomly,
however there's nothing labelled 82S100 in this machine. Maybe it's
labelled with a different part number for these machines? Far as I know,
the machines are supposed to be C64 compatible...
The second
machine is totally dead - no activity whatsoever. There's a
*very faint* humming noise from the monitor area, typical of a display
that's at least getting power though - but on the CPU side of things no
chips seem to be getting remotely warm, suggesting that there's no +5V.
A voltmeter will verify the truth of that last statement, but alas the
voltmeter that does tests over the internet has yet to be invented :-).
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
20 Jul
20 Jul
12:16 p.m.
Hi Jules,
I have an SX-64 myself that I still use to this day. I have seen the fault
that you describe in the first system a few times before and have always
managed to clear it by reseating the socketed chips and reseating the
connections between the boards themselves. Particularly the connection of
the board that runs vertical, as you look at the front of the system, at the
back to the board perpendicular to it. That one connection tends to work
itself loose over time from the bottom of the board up.
Greg Manuel
-----Original Message-----
From: cctech-bounces(a)classiccmp.org
[mailto:cctech-bounces@classiccmp.org]On Behalf Of Jules Richardson
Sent: Saturday, July 17, 2004 5:16 PM
To: classiccmp(a)classiccmp.org
Subject: Commodore SX64 probs...
I've got a pair of non-working Commodore SX64's here.
One machine powers up, but the floppy drive light remains lit and I can
hear the drive spinning continuously, and there's a 50% grey pattern
filling the screen (i.e. pixels look to be alternating white/black).
Actually, there's also short run of pixels middle-bottom of the screen
which aren't illuminated at all. Pressing reset has no effect. Pressing
caps-lock does result in the caps-lock light illuminating, but I don't
know if that's a simple circuit hardwired to the key and doesn't go via
the CPU...
The second machine is totally dead - no activity whatsoever. There's a
*very faint* humming noise from the monitor area, typical of a display
that's at least getting power though - but on the CPU side of things no
chips seem to be getting remotely warm, suggesting that there's no +5V.
Before I start digging deeper, does the fault with the first machine
sound familiar, and are there any common PSU faults which affect these
systems? Plus, anyone have schematics they could scan?
Be nice to get one of them going. One keyboard is damaged (plus I only
have the one original keyboard cable), so it's only really viable to
have one running, but I'd like to get to the bottom of what's up with
both of them...
cheers,
Jules
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21 Jul
21 Jul
8:43 a.m.
On Wed, 2004-07-21 at 00:16, G Manuel (GMC) wrote:
Hi Jules,
I have an SX-64 myself that I still use to this day. I have seen the fault
that you describe in the first system a few times before and have always
managed to clear it by reseating the socketed chips and reseating the
connections between the boards themselves.
Not so these ones unfortunately. However, I put the word out locally
that I was after a C64, and someone came through with the perfect
machine - working, but with a scratched case and broken keyboard. Ideal
as a source of chips :)
I ended up replacing the SID, PLA, and both CIA chips on the I/O board
in one machine in the end. It now runs - I'm just matching up the best
bits of case to make one presentable system. I haven't tried the floppy
drive yet though - fingers crossed that's OK...
cheers all,
Jules
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