Commodore PET 2001

[ajgriff]

Originally Posted by ajgriff

It just so happened that either PIA1 or the VIA in the PET was also faulty although I haven't yet established which of them was causing the problem.

Having studied the schematic more carefully I realised that PIA1 reads the datasette signal from J6 (internal) and the VIA reads from J3 (external). Bearing in mind that I've been using the internal datasette connection for testing it seemed logical to assume that the PIA was the culprit. I replaced the original VIA this morning and the PET still reads the short test programme so PIA1 had indeed caused the problem.

Both PIAs have now been replaced. As previously mentioned I may have caused the failure of one of them (PIA2) by hot-plugging. However the strange read signal was evident prior to PIA2's demise so I think the PIA1 fault was there all along.

Alan

[ajgriff]

This is hard to credit but I'm now struggling with another unexpected problem. Foolishly I thought I'd just make sure that the datasette functions correctly when connected to the external (J3) VIA port. I entered the load from tape #2 command and the PET searched before moving on to the FOUND statement. Next, instead of reporting LOADING as you'd expect, the screen scrolled to a blank display and froze. The datasette just carried on in play mode. I tried swapping the VIAs to no avail. Finally I did confirm that eveything still works properly using the internal (J6) PIA1 port. I'm stumped yet again.

Help!

Alan

[SiriusHardware]

As you seem to have eliminated the digital side of things by swapping the relevant large ICs, and assuming you aren't unlucky enough to have identical faults on PIN 18 (Cass Read #2) of both VIAs, how about the analogue side of things - does the tape look as though it's running at the right speed when powered through Q2/Q1 rather than through Q5/Q4?

[ajgriff]

Analogue? What's analogue?! Seriously though that could be inspired thinking. I didn't notice a speed issue but well worth checking out the motor voltages at the two ports.

Alan

[ajgriff]

It was a good thought but the under load motor voltages turned out to be virtually identical at each port. After checking that out I used the tatty C64 type C2N so that I could compare what was happening at each port without constant shutdowns for plugging/unplugging. After an initial re-appearance of the fault I was unable to replicate the problem after multiple save/load operations using all combinations of ports and datasettes. The only explanation I can offer is the possibility of slight oxidation on J3's contacts which have cleaned up with use. Anyway panic over. I'm afraid I've got to the point where I'm expecting the PET to fail at every turn. Thank you all for your patience.

Alan

[ajgriff]

I think this would be a good moment to declare the repair and restoration of this Commodore PET 2001-8 Serial N° 1008715 as officially complete although there are a couple of loose ends I'd like to tidy up in the fullness of time:

1. I'd pleased to find the books, documentation and tapes that came with the PET when I bought it all those years ago.

2. Similarly it would be good to locate the original datasette.

One of the difficulties with threads of this length is the challenge faced by future restorers in finding concise information to help with their particular project. Much of the information is out there but is scattered across many different internet sites and forums like this one. As a result I've decided to prepare a Success Story write up of the project summarising the main points, documentation and resources I found useful. The datasette became a mini-project in its own right so I'll do a separate write up dedicated to that part of the overall exercise.

Finally I'd like to express my heartfelt thanks to everyone who has contributed to this thread. I'm not going to highlight individuals as I think that would be unfair. Suffice to say that your collective knowledge, support and encouragement have been invaluable.

Alan

[ajgriff]

This is a bit of an aside to the main plot but I've been doing some refurbishment work on the C64 style datasette in order to provide the PET with an additional tape drive for use with its external port.

Inspired by Tim's (tim.norris) recent experiments with his Bush transistor sets I decided to try out the Retro0bright process. The datasette was an obvious candidate for treatment as illustrated by the first photo. This was very much a 'quick and dirty' trial so I wasn't expecting spectacular results. Basically I brushed a coating of cream peroxide (hair product) on to the top half of the case, wrapped the it in cling film and put it on a roasting tray lined with aluminium foil which was then postioned outside on a south facing window sill for four hours (turning occasionaly).

Unfortunately it's not been that sunny here today. In fact most of the time it's been bright but overcast. Nonetheless I'm quite surprised at the outcome as shown in the second photo. I guess it might benefit from a little more sunbathing but on balance it looks like the Retr0bright process does indeed work.

One of the difficulties I have now is that I keep looking at the PET's yellowed keys and thinking about the possibility of Retr0brighting them. Any advice, particularly on safe removal of the keys, would be appreciated.

Alan

[Timbucus]

That is quite an improvement - several pundits on the retro computer scene also swear by just putting them out in the Bright Sun without the Peroxide. I did this with my Amiga and the difference was noticeable after a few hours. YMMV Can't help on the keys sorry never seen a chicklet PET!

[SiriusHardware]

My gut feeling is that the peroxide will do terrible damage to what I think are brushed aluminium key tops. Mind you, I have been surprised when people have retrobrited the likes of the keys from the Atari ST, Amiga and so on where the key legends are printed on, I am amazed that the process does not seem to do any damage to the legending on that type of keyboard.

In the case of aluminium key tops though I honestly would not risk it. Those key legends can't be very resilient to begin with given their legendary(!) tendency to rub off after one too many games of Space Invaders.

I am tempted to try this with my original Atari ST which is so badly sunburned it is a sickly shade of tan, nothing like the pristine battleship grey it was when we were both young.

[Slothie]

I wouldn't put peroxide anywhere near the aluminium keycaps on a pet. If you watch any of the retro computing youtubers doing it they always carefully remove any badges, especially the shiny aluminium backed ones. I don't think it would be possible to remove the keycap legends without damaging them. If the plastic is truly offending to the eye, then I would recommend carefully masking the legends with some kind of tape and then giving them a light respray with some kind of ivory paint. Either that or leaving them out in the sun as Tim suggests, although I would worry about the colours on the keycaps fading.

[ajgriff]

So the general view is that it's safe to rub on your head but not worth risking with precious PET chiclet keys.

Seriously though I'll give the points raised due consideration in the light of the chemistry involved. Long time since I studied the oxidation and reduction of chemical compounds so I'll need to do some re-learning before making a decision. This machine has really got under my skin which is odd because I began the project with an attitude of relative indifference towards it. I blame lockdown boredom but perhaps it's just my nature.

Alan

[Slothie]

TBH I wouldn't put peroxide near my head either, but I definitely wouldnt put it on my head then sit for hours out in the full sun afterwards!
If you had a spare key you could try that but I presume you haven't any, and when I've seen spare keys on ebay they've always been a ridiculous amount.
Although casual googling seems to imply that aluminium and peroxide wont react much at all, but that can't be said for the dyes that are used in the anodising that forms the labels.

[SiriusHardware]

Peroxide is also the base component of one type of ear wax clearer. Suffering from bewaxed ears at one time, I asked the nurse clearing my ears in the conventional way (with low pressure warm water) whether I should just use the peroxide stuff in future and I was told in no uncertain terms what a stupid idea that would be - and I was talking about the stuff which is made for that purpose and available at any chemist. Seems peroxide in your ears is even worse than on your head.

The crux of the matter is that you can usually replace your skin cells or your hair, but your Commodore keys are a one-off.

[ajgriff]

Ok I completely accept that a PET chiclet key really is more precious than various body parts, not that I'd use peroxide on my head or in my ears either! I agree that the main risk in terms of Retr0brighting comes down to the possibility of removing the printing from the keys. The PET obviously doesn't like the idea either as it's tried to distract me with another little problem today. More on that to follow.

Alan

[Mark1960]

I think vintage computers are like vintage cars, they have to be used to really appreciate them, and they require a lot of care and attention to keep them running, but then thats all part of the fun and why we get so attached to them.

[ajgriff]

As if to illustrate Mark's point the PET kindly pointed out that its newly refurbished datasette wasn't auto-stopping as it should when in play or record mode. I think it still rather resents the fact that I 'lost' the original unit.

Took me a while to figure out how auto-stop is supposed to function. Basically when the spool freezes the tightening tape bears against the sensor 'A' (see first image). The sensor only moves into position when the head carriage moves forward ie, when play or record are active. Movement of the sensor is transmitted via a series of levers and pivots to the actuator head 'B' which should then flick against the stop slide thus releasing the keys (see second image). All a bit overly complex in my view.

Everything seemed to be moving freely enough and I couldn't immediately see the cause of the problem. Naturally it all came down to dried grease in the end. Took a while to clean things up and re-lubricate partly because of the need to avoid contaminating the tape path. All's well now though and the datasette is back in the PET.

Alan

[ajgriff]

Not much sunshine here today but I thought I'd give the bottom half of the C64 type C2N case the peroxide treatment anyway. I mention it because I was particularly interested in any effect the peroxide might have on the datasette's label. The label is black print on a silver background and therefore quite similar to most of the PET's keys. I made sure that the label received a thick coating of peroxide cream.

The results are shown in the attached photos. Again the case has responded well although it could do with another session on a sunnier day. As far as the label is concerned I can't detect any discernible effect resulting from peroxide or UV exposure. I wonder if the same would be true of chiclet keys?

Alan

[SiriusHardware]

You're obviously determined to do it... so....

[ajgriff]

Decisiveness isn't one of my strengths Sirius .....

Alan

[Timbucus]

Originally Posted by ajgriff

Decisiveness isn't one of my strengths Sirius .....

Alan

That statement was pretty decisive