Re: Non-working Commodore PET 3016
 

And when it does so, does it stay shifted for a significant amount of time or is it only a very brief blip / jump / shift and then back to normal? How often is it doing it - several times a second - several times a minute?

Re: Non-working Commodore PET 3016
 

Very brief shift up and down. It does it several times a minute.

Colin.

Re: Non-working Commodore PET 3016
 

One more question: Is the fault progressive? In other words, is it mild or not there at all when the machine is first switched on, and then does it begin and become more more noticeable as time goes on?

or-

Is it there more or less as soon as the machine is turned on, and does the frequency - the number of times it happens per minute - remain more or less constant no matter how long the machine is on for?

Re: Non-working Commodore PET 3016
 

The latter. I've tried to get a video to show you what's going on. It's more obvious (and annoying) in real-life, but you can see it at its worst about 30s into the video.

https://drive.google.com/file/d/16oI...ew?usp=sharing

Colin.

Re: Non-working Commodore PET 3016
 

That looks like vertical hold being lost for a moment - missed frame pulses or the like?

Re: Non-working Commodore PET 3016
 

Perhaps I shouldn't have cleaned the already working CRT board, but it was filthy....

Colin.

Re: Non-working Commodore PET 3016
 

Well, let's think. Colin never mentioned the monitor doing this prior to the stripdown (he probably would have noticed it before then) so I think what we probably have here is a case of physical disturbance or change during the makeover rather than a new electronic fault.

I think something physical has changed - could be the position of a pot / preset, or the legs of a component 'connected' together by liquid which has not dried out, etc.

To begin with can you check that the thick rubberised cable leading from the tube cap to the top of the line output transformer is more or less as it was before, with the rubber cable kept well away from anything else on the way between the tube cap and the LOPT (Line OutPut Transformer).

Also try just reseating the display connectors at both ends of the cable which carries the video signals from the main board to the monitor. (Do that with the power off).

We'll need to find the right circuit for your particular monitor to see if there is a vertical hold or vertical position pot which may have just gone a bit noisy or had its value changed slightly.

Re: Non-working Commodore PET 3016
 

No you were correct - it is better to remove any dirt and then correct any issues as dirt can cause worse faults as it can trap damp etc...

Re: Non-working Commodore PET 3016
 

You've put me on the right track; thank you. I've fiddled with the green circled pot on this photo and that seems to have stabilised things.

Colin.

Re: Non-working Commodore PET 3016
 

Looking around other corners of the net there is mention of an earth bonding strap or wire between GND on the main computer section and GND on the monitor. Does your machine have that feature?

Edit: Just caught Colin's post re: Pot adjustment. Let's hope it really was that simple. Try to watch it for at least half an hour without blinking, otherwise you'll never really know. ;)

Re: Non-working Commodore PET 3016
 

If I'm looking at the right component layout diagram and then the right circuit diagram that would appear to be R621 (maybe that's marked on the PCB) - if so that's the vertical height control, so it is at least involved in the vertical aspect / section of the circuit.

Re: Non-working Commodore PET 3016
 

Circled from above here - there's no component markings on either side of the monitor PCB.

Colin.

Re: Non-working Commodore PET 3016
 

Its possible during cleaning you unintentionally moved it and it just needed readjusting to get vertical lock, or maybe its noisy. Lets hope its finished trying to get your attention!

Re: Non-working Commodore PET 3016
 

OK, I had the wrong circuit layout and diagram.

For reference, this layout is the one which matches the PCB and layout of Colin's monitor PCB.

http://www.zimmers.net/anonftp/pub/c...deo-layout.gif

Note the awkward error on that diagram - while the parts are shown, correctly, as they would look from above, the copper trace diagram is shown as it would look from below the board instead of, as it should be, looking through the PCB from above. The line output transformer is shown upper left, but the PCB pads it should be soldered into are shown upper right. The copper trace outline needs to be flipped over left / right.

Just to complicate matters further there are three distinct versions of the monitor circuit built on that PCB, namely

http://www.zimmers.net/anonftp/pub/c...01/video-1.gif

http://www.zimmers.net/anonftp/pub/c...01/video-2.gif

http://www.zimmers.net/anonftp/pub/c...01/video-3.gif

It would take a bit more investigation to work out exactly which one corresponds to Colin's but luckily his tweak to R20 (which is the 'vertical height' control in all three versions) seems to have sorted it out for the time being.

Re: Non-working Commodore PET 3016
 

Stickers back on, using the suggestion from ajgriff of double-sided tape (which I happen to have in 6mm, 9mm and 12mm wide rolls).

I think that's the last thing now. I'll post that summary later on tonight to round this all off.

Colin.

Re: Non-working Commodore PET 3016
 

OK - here's the overall summary of this entire mammoth thread which started on the 1st January this year and has 1835 posts (including this one), and has 35,450 views.

I had a broken 3016 and had it since 2012. It had power and I could see the monitor's orange colour in the back of the CRT tube, but that was it. The first person to reply was SiriusHardware, and I know lots of other people helped out, but he stayed with me all the way. I could not have done this without his help, patience, and logical approach. It's even more remarkable when he said he's never even seen a PET.

I didn't want to get it back to how it left the factory - it had a few dents and bruises and I wanted to keep them where I could. Its source had been scratched into the case - Kendall College of Further Education and I've managed to keep them through the rub-down/re-spray. I also managed to keep the QC stamps on the inside of the case that no-one will ever see, but it seemed important to me to keep.

I've learnt so much - I've put a blog post up here which lists all that I have learnt, and has lots more photographs.

https://colinjhaynes.wordpress.com/

I've replaced 17 chips and added 18 sockets (the difference is a chips that checked out OK but their sockets didn't, including the 6502).

The chips replaced were:

UA7
UA8
UB2
UB3
UC3
UC4
UC9
UE7
UE8
UE10
UF7
UF8
UF9
UG5
UH1
UH3
UH6

And Sirius kindly burnt me a new UD7 PROM as that one was faulty.

I spent pretty much exactly £300 - £40 on point, £150 on sockets and chips, £80 on meters and on a USB oscilloscope and the remainder on sundries (an Arduino, motherboard stand-offs, leaded solder, user-port interfaces etc).

We dealt with a faulty IEEE port and a faulty datasette #2 port. I got advice on how to remove and reattach the stickers, how to discharge a CRT (which seemed important to know really).

It seemed that others got interested in this thread and I had more than one private message encouraging me along.

I'd really like to thank every single person who chipped in with help, advice, testing code, kind queries on my duff scope readings and general tolerance of my sometimes naive questions. It's been a brilliant lockdown project and there's one PET rescued to add to the collection now.

Thanks everyone - I think we're done now until it breaks again. Anyone who ever manages to travel to Perth must give me a shout so I can buy you a pint.

Colin.

Re: Non-working Commodore PET 3016
 

Congratulations on getting it both working and cleaned up. I’m guessing a large portion of the spend was on shipping due to placing orders on one chip at a time.

Re: Non-working Commodore PET 3016
 

There was a lot of P&P in there for sure, but having thought it through, there really was no other option other than to only order when it was clear that one (or a pair) had failed really.

Colin.

Re: Non-working Commodore PET 3016
 

Actually, you sorted that yourself as you got the replacement from 1980s_john. ;)

It has been a great pleasure to observe not only the computer but you yourself making steady progress as the project progressed - you probably didn't notice, but in the beginning we were being quite specific about what to look at and how to do it. By about half way through you were correcting our (...my...) circuit diagram reading blunders and near the end we were asking you to do things and you just... did them.

It's an old machine, so if it hits any more bumps in the road you know where to find us, but quite honestly, I'm not sure you'll need us any more.

All the best, and enjoy your PET.