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_at_solutionengineers.com>
To: <classiccmp_at_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:
> >> >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,
> >
> >Well, this is good practice, then :-)
>
> True :) It does seem a shame to practice on such a rare piece of kit,
> somehow...
>
> >> 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 :(
> >>
> >> >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
> >
> >What test equipment do you have?
>
> Erm, a multimeter...
>
> I'd have to buy a 'scope, and they're not cheap...
>
> >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).
>
> 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
>
>
Received on Wed Aug 22 2001 - 10:30:28 BST