22 Aug
2001
22 Aug
'01
10:30 a.m.
There are relatively inexpensive ($20 US) multimeters that can measure frequency
up into the tens of megahertz that would be helpful. If you are measuring a
clock, it will tell you right away whether it's right. It won't tell you much
if it's wrong, though. It does give you more information than just measuring
voltage.
Test equipment is expensive, but hardly anyone wants the "old" stuff that once
was perfectly adequate for precisely this class of equipment. A 'scope with two
probes, delayed sweep timebase, and a bandwidth in excess of 20 MHz (e.g. TEK
935) is probably adequate. If you shop around, you should have no trouble
finding a TEK 465 (100 MHz) that's quite complete and functional for somewhere
on the order of $250. Over time, these will become less available, however. My
old '465 is still the workhorse around my place, though I have faster, fancier
models.
As classic hardware ages, it's likely to break and you'll want to be able to fix
it, since the technology of the '70's and '80's renders this stuff
inherently
repairable.
It may be painful to learn, but it's very satisfying when you breathe life into
what was a "dear, departed" computer from yesteryear.
Dick
----- Original Message -----
From: "Adrian Vickers" <avickers(a)solutionengineers.com>
To: <classiccmp(a)classiccmp.org>
Sent: Wednesday, August 22, 2001 2:47 AM
Subject: Re: CBM 8032 SK
At 11:22 pm 21/08/2001 +0100, you wrote:
Well, this is good practice, then :-)
True :) It does seem a shame to practice on such a rare piece of kit,
somehow...
Erm, a multimeter...
I'd have to buy a 'scope, and they're not cheap...
The latter, although according to the chap I got it from, it uesd to bleep
at power on, but with nothing on the screen. However, when I put the (now
known to be) dead CPU in my working 8032, the monitor failed to whistle
like it ususally does; so it's _possible_ the monitor will be OK.
Right, I shall go look up logic probes & think...
Cheers!
Ade.
--
B-Racing: B where it's at :-)
http://www.b-racing.co.uk
The ROM's are probably pin-compatible with some
flavor of EPROM, and
somebody,
somewhere, surely has the working ROM's ...
Hmm, possibly. I suspect it's going to involve many hours of slaving over a
hot soldering iron, and TBH my soldering's just not that good. Besides, Maplin
seem to have mislaid my order for a bunch of soldering-related kit
(e.g. the desolderer), so no major surgery can take place yet :(
What test equipment do you have? If you can locate that stuff, perhaps it will be
easier to effect repairs
than
to find the complete and functional
heart/lung/brain, eh?
Possibly. The trouble is - where can the problem lie? The machine is either Start by checking all the power rails (at the pins
of the chips) with a
voltmeter. Get the PSU working first.
Done & tested. Power is OK.
Then use a 'scope, logic probe or logic
analyser (yes, OK, I have
somewhat fancy test gear) to check the clock input to the 6502.
Actually, I used the voltmeter for that; it reads approx half the normal
input voltage, which *suggests* that its OK.
If
missing, fix the clock circuit. Check the reset pin while you're at it,
to ensure the machine is not stuck in the reset state. Without good
power, clock, and reset, the machine is not going to do a lot.
Reset is OK too, so theoretically (and assuming the clock really is
ticking, and not just stuck at a constant half voltage) the CPU is getting
what it'll need.
Then use the same instrument(s) to check the phi2 (bus clock output) of
the 6502. And look for activity on the address/data buses.
The clock outputs register lower voltages than the clock in (0.93v and
0.75v). However, that tells me pretty much bugger all, I will need some
better kit to really examine those.
When you've got this far, it's then time
to see just what ROM(s) are
being selected (logic probe, etc on the CS/ pins) and thus what the CPU
is doing. Unless, of course you have a logic analyser that can look at
all 16 address lines at once.
This is realms of the unknown for me - I shall have to go look up logic
probes/logic analysers... I assume the same sort of checks can be done with
most chips, e.g. RAM, ULAs and so forth.
not
starting up, or the beeper is dead (and without the screen, the beeper
Is there known to be a fault with the monitor, or do you just get nothing
on the screen. If the latter, the monitor might be fine and the fault due
to the mainboard never outputting video data (the CPU has to initialise
the 6845, etc for the monitor to display anything, so you need to debug
the CPU side first).