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 - 03:47:20 BST