--- JP Hindin <jplist_at_globe.net.nz> wrote:
>
> Greetings all,
> Picked up a CBM 8032 today, amongst other good stuff a little more
> recently produced.
Fun.
> I've plugged in and attempted to power it up, but I get zip... Bad power
> supply I guess?
Perhaps. The PSU is a linear one, easy to fix. The transformer
needs to be putting out ~18VAC-22VAC to the twisted pair of brown
wires going up to the monitor. I don't know the exact voltages
of what goes onto the motherboard, but there are a pair of +5VDC
regulators in the heat sink, plus, IIRC, +12V and maybe some
extra goodies, too (4116s are multi-voltage).
If you don't get a decent amount of AC voltage to the monitor, or if
you don't see +5V on the expected corner pins of the TTL chips, you
have a PSU problem. Look for oxidation/discoloration of the PSU
connector where it attaches. Too much current draw causes the connector
to break down, resistance increases, causing more current draw - rinse,
repeat. I've seen some of the plastic PSu connectors blackened and
blistered.
> Anyone got any experience with these units, and/or fixing them?
Yes. If you _do_ have all the right voltages, try reseating all
the connectors and socketed chips. Barring that, anything from
a bad ROM (yes, I've seen that happen) to a bad CPU could cause
things to go wrong. I happen to have test clips from a Commodore
dealer, so I can use them. An oscilloscope can show that the
CPU is clocking along - with a spare CPU chip, you can bend out the
data pins and short certain ones together to cause all reads to
return $EA - the NOP opcode - The CPU should fetch the reset vector
($EAEA) and begin executing from there... The idea is you mangle
up a CPU, then watch the address lines strobe up to show how
various parts of the board are working. It helps identify stuck
bits and bad selector logic.
If necessary, I could photograph one that I received from the
local C= dealer when they closed and I bought out the service
department (10 years ago).
Schematics, firmware, etc., are available at ftp.funet.fi.
> My favourite feature so far:
> The keyboard/monitor tips up and backwards and there is a prop rod to
> hold the upper chassis up, just like a hood prop :)
Yep. Don't let the top fall on you. Trust me.
-ethan
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Received on Wed May 22 2002 - 17:41:38 BST