At 02:32 am 23/08/2001 +0100, you wrote:
>> >Err, are PETs rare? They seem pretty common compared to the stuff I=20
>> >learnt computer repair on (Philips P850). I've never thought of the=20
>> >8032SK as being a particularly rare PET either (It was the first CBM I=20
>> >obtained, which might affect my judgement here).
>>
>> It depends which one... I've not seen many 8032SKs about (I still curse t=
>> he
>> day I had to hand the working one I was using back to its rightful owner)=
>> ,
>> probably because they're either rotting away forgotten in lofts, or
>> collecters who have them won't give away/sell them. I don't blame them, t=
>> he
>> 8032SK is an inspirational piece of design, even now. Well, until you loo=
>> k
>> under the cover and see that it's a right hotch-potch...
>
>Actually, I think it's a stupid design.
Erm, I was thinking more of the way it looks on the desk...
>The 'separate keyboard' seems
>nice until you move it away from the machine, whereupon the keyboard
>cable unplugs itself from the DB25 on the main unit.
I never found that to be a problem, although I mostly used it with the
keyboard in it's looks-like-its-attached position; It would probably have
been better with an IDC connector (ala the Osbourne).
> The thing is just
>too wide to fit on a shelf in a 19" rack.
They're supposed to sit on desks, not racks...
>And the wires to the monitor
>are too short to easily open the case with the monitor still on top of
>it. No, I don't like the design at all.
>
>I assume you realise it's a normal 8032 motherboard in there, rotated by
>90 degrees and with cables connecting the user port and GPIB edge
>connectors to the Amphenol Blue Ribbon connectors on the back. It is,
>AFAIK the only PET not to need a special GPIB cable for the link between
>the machine and the first peripheral.
Internally it's a mess. The PSU is in a crazy position; the 240V supply
line is too short and stretches dangerously if the unit is opened to
90degrees, the balance is all wrong, and yes - it's just an 8032 board
rotated (although there are subtle differences between the -SK board and
the regular board, although that may just be down to different revisions
between the machines. The only reason it doesn't need a "special"
PET-->IEEE cable is because it already has one internally... Useful,
because I've plundered it to test the diskdrives I've now got with the
regular 8032 (and they work nicely!). Shame they didn't bother to put the
plastic keys in, so there's the possibility of putting it on upside down -
luckily that didn't happen to me. Oh yes, the monitor signal & power cables
go through a connector which floats in the middle of the machine - it looks
like someone forgot about that until the last second...
>> >> I'd have to buy a 'scope, and they're not cheap...
>> >
>> >You can get _good_ second-hand 'scopes for less than a poor quality new=20
>> >one. Stewarts of Reading often have Tektronix 'scopes for a few hundred=20
>> >pounds (something like a 465 or a low-end 7000).
>>
>> Which would you recommend? I'd pay =A3200-=A3300 for something that's goi=
>
>Don't buy a new low-end 'scope (certainly not one of the Lucky Goldstar
>or whatever that Maplin sells (I think the 'Lucky' part of that brand
>name describes what you are if it works properly :-))). The Tekky 465 is
>a small-ish portable instrument. The 7000 is larger, but it takes plug-in
>modules, which means you can get (or could get) various special-purpose
>plug-ins. That's not too useful unless you have some special applications
>and _can get the right module_.
I think simple, but reasonably useful for now at least; I may need fancy
stuff in the future, but I'd prefer a "beginners" instrument for now. I'll
go with the Tex 465 then, if I can get one, or I'll ask them which they
recommend on a similar level.
>
>I would probably go for the 465 in your case. For me, I'd go for a 7000
>(my old, valved, 555 has plug-ins, and some of them (1GHz sampler,
>spectrum analyeser, etc) are fun...
>
Hmm. Valves. There was a whole branch of electronics which finished (um,
ceased to be mainstream, I should say) before I got started...
>> >I notice you're in the UK, just out of curiousity where are you (I'm in=20
>> >SW London), just in case there's somebody near who could at least do a=20
>> >few tests for you.=20
>>
>> Just up the road from Tower Bridge (E1) mostly; when I'm not down here, I=
>
>That's close enough to me (i.e. it's near a Tube station :-)) that it
>won't take much persuading to convinve me to appear with a logic analyser
>or similar if necessary. It's probably better if you do some more work on
>your own (you'll learn more that way....)
Agreed. If I don't get the basics learned first, I'd just end up a spare
wheel...
>> >Excellent. You'd be amazed how many problems are PSU-related, though...
>>
>> I can imagine. 12v will fry a TTL chip, won't it? All the working PETs I'=
>
>Very easily....
>
>> ve
>> got have some screen wobble, so it's possible that the PSUs are getting
>> borderline with age, unless that's what they always did - except through =
>
>Sounds like the large capacitor(s) are drying up. Or on the models with
>them separately mounted on the chassis, the connector linking them to the
>mainboard has gone high-resistance (another common fault!).
I'll check that. I had to remove the whole gubbins from my working 8032
when the mains filter exploded, but I didn't check any resistances/voltages
there. All the connections have been un-made then re-made, so if the HR
usually comes from mucky connectors, that's unlikely. If the cap is going,
however, moving it around would have no effect.
Is there any way to test for a drying cap?
>> >OK... Is RDY mostly high at the CPU (or could this darn thing be stuck i=
>> n=20
>> >a wait state)?
>>
>> IIRC, I checked that accidentally (got the wrong pin when checking the
>> voltage), and it seemed to be stable at 5.23v; depending on how often it'=
>> s
>> supposed to drop, I don't know if that's a good or bad thing.
>
>If it's high, the CPU will be running (or should be running). It's not
>stuck low, and thus I think it's likely that this is not a problem... (it
>would be a total coincidence if it pulsed low very briefly at just the
>right time to start a wait state on every cycle...)
Unfortunately, the CPU *is* kaput, but (as mentioned elsewhere) I'm not
happy putting a spare (i.e. one from another machine) in until I'm totally
sure the bad board isn't going to kill it.
>>
>> I'll give Stewarts a call tomorrow, if I remember. Are they likely to hav=
>> e
>> logic probes as well?
>
>They do sell other test gear (mostly second-hand). They often have logic
>analysers (at various prices, not necessarily cheap :-(), dunno about
>smaller stuff...
No harm in asking... I may drive out on Saturday and have a look, if
they're open.
>
>> >Be warned a new logic analyser is an expensive instrument, and is likely=
>> =20
>> >to be way out of your price range. But a lot of older logic analysers,=20
>> >which 'only' go up to 100MHz are available second-hand. While they're no=
>> t=20
>> >all that useful for many modern chips (I will not say 'useless', becuase=
>> =20
>> >I've used them to debug such systems), they are idea for 99% of classic=20
>> >computers. You might find one for \pounds 50.00 or less if you hunt=20
>> >around (say at radio rallies). Something like a Gould K100D would be=20
>> >ideal, I think.
>>
>> Maplin do a single-point probe for about =A350; Farnells do a couple more=
>
>That sounds a little high. About \pounds 25.00 is more reasonable, I think.
Maplin, innit. Not exactly the cheapest on the block...
>> but their full logic analyser is about =A3500 (and looks suspiciously lik=
>> e an
>> oscilloscope with the knobs replaced with a keypad). I'm not out to spend=
>
>And rather different internal electronics....
:)
>
>> a
>> grand on test kit *just* yet; especially not if there's some good s/h gea=
>
>No, I am not suprised....
GBP500 is reasonable, I'd say, so long as the kit is going to last a while
and do most of the stuff I need of it. I can always sell it on later, of
course, when/if I need to upgrade.
>> >You need a 'scope as well -- a logic analyser is only useful if the=20
>> >signals are known to be logic-level signals.=20
>>
>> Did anyone ever do a combined logic-analyser/'scope?
>
>Yes... Tektronix and HP both sold logic analyser plug-ins for some of
>their scopes (the Tektronix 7D01 for the 7000-series scopes, and HP did
>one for the 180-series scopes that I can't remember the number of, but
>which I have the service manual for somewhere).
That sounds ideal, but probably overkill for what I want - especially right
now...
>
>Tektronix also did a portable logic analyser system (it had a gas plasma
>display on top, and could also drive a VGA monitor IIRC) for which one of
>the option boards was a digital sampling scope. It was NOT CHEAP, though...
:(
What about one of these software oscilloscopes? I think the only one I've
seen was a picture on EPE's website, but there must be a few of them
surely? Mind you, hardly a portable device if you need a pentium PC within
reach...
Cheers!
Ade.
--
B-Racing: B where it's at :-)
http://www.b-racing.co.uk
Received on Thu Aug 23 2001 - 04:29:50 BST