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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 26th Sep 2022, 8:59 pm   #121
ScottishColin
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Default Re: 1978 Commodore PET project

Is there any merit in me bending out UE7/3 here to have something to compare to? Mine has been replaced so is socketed so it'll be easy to do.

Colin.
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Old 26th Sep 2022, 9:01 pm   #122
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Default Re: 1978 Commodore PET project

The contact pads of the chiclet keyboard can be cleaned/restored without removing the keys as demonstrated in the video mentioned by Colin in post #66. I'd strongly advise against key removal.

Alan
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Old 26th Sep 2022, 9:17 pm   #123
SiriusHardware
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Default Re: 1978 Commodore PET project

Quote:
Is there any merit in me bending out UE7/3 here to have something to compare to?
I don't think so Colin, but thanks anyway. Your measurements earlier made it quite clear that there is a fault on the UE7 / UF7 / UF9 node though, so that was a very valuable contribution.

We were just trying to think of how to replace the smallest possible number of devices necessary in BrackenFix's machine, but as he has already ordered replacements for all three I'm not sure if it wouldn't just be simpler to replace all three (one at a time, stopping at the point where the fault goes away) provided BF is completely happy that he can safely snip, remove and replace them.

I agree that looking at the keyboard is good use of the intervening time, so maybe we can all stand down until BF lets us know when the replacement chips have arrived.
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Old 26th Sep 2022, 9:37 pm   #124
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Default Re: 1978 Commodore PET project

I will keep you all up to date.

Luckily, I'm filming everything so you can see what I have done lol

Will start on the keyboard in the next day or so
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Old 27th Sep 2022, 10:05 am   #125
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Default Re: 1978 Commodore PET project

The attached image shows my PETís very grubby chiclet keys after cleaning in situ (ie, without removing the keypads). I used nothing more than a damp (not wet) cloth using warm water with a drop of washing up liquid added. It was a fiddly and time consuming task but there was no risk of breaking the plungers. The yellowing is the result of age and exposure to light. They could be whitened using the retr0bright process but this would again require keypad removal and I also donít want to run the risk of lifting the print.

With regard to de-soldering ICs, am I right in recalling that BrackenFix has bought a de-soldering station and some leaded solder? If so Iíd suggest some soldering and de-soldering practice on a scrap PCB would be very worthwhile as mentioned earlier in the thread.

Alan
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Old 27th Sep 2022, 10:31 am   #126
BrackenFix
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Default Re: 1978 Commodore PET project

Hello

I am indeed getting a desoldering station and have got leaded solder and a practice board waiting

I will definitely be careful with the keyboard and don't want to remove anything that isn't absolutely necessary
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Old 27th Sep 2022, 4:59 pm   #127
Mark1960
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Default Re: 1978 Commodore PET project

Is there any way to verify the operation of the keyboard interface on the main board before starting any disassembly of the physical keyboard?
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Old 27th Sep 2022, 5:06 pm   #128
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Default Re: 1978 Commodore PET project

The keyboard is just a matrix of switches, all the electronics is on the main PCB. Therefore briefly connecting a wire betweem a 'row' pin and a 'column' pin on the keyboard connector will simulate pressing a key. I am sure the electrical layout of the keys is in some available documentation.

However you do of course require a working main PCB for this to be useful. So that video fault needs fixing first.
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Old 27th Sep 2022, 5:42 pm   #129
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Default Re: 1978 Commodore PET project

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Originally Posted by Mark1960 View Post
Is there any way to verify the operation of the keyboard interface on the main board before starting any disassembly of the physical keyboard?
In his latest video BrackenFix is shown over-typing zeros using some of the working keys so I guess we can assume that the interface is working ok.

Alan
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Old 27th Sep 2022, 5:58 pm   #130
BrackenFix
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Default Re: 1978 Commodore PET project

A few keys seem to work, especially if you press a bit harder than normal.
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Old 27th Sep 2022, 6:05 pm   #131
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Default Re: 1978 Commodore PET project

The last few minutes of the video posted by Colin show exactly what you need to do to get all the keys working. Here's the link again for ease of reference:

https://www.youtube.com/watch?v=WMKECAQjCH8

Alan
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Old 27th Sep 2022, 6:11 pm   #132
ScottishColin
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Default Re: 1978 Commodore PET project

Sandpaper is a bit interesting.

I used a sheet of plain A4 from my printer, folded it a few times and gently ran it over the plungers. It fixed most of the keys. For the few that didn't work, a slightly more vigorous going over with the paper fixed the problems.

Colin.

EDIT - I also cleaned the PCB with 99% IPA while I was there, but mine was nicely new (apart from a couple of broken traces) having been sealed up for 40+ years anyway. You might not need to do this if the cleaning plungers works.
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Old 27th Sep 2022, 6:29 pm   #133
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Default Re: 1978 Commodore PET project

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Sandpaper is a bit interesting.
Use the finest grade of carbide paper you can get hold of. Finish off by wiping with IPA.

Alan
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Old 27th Sep 2022, 6:53 pm   #134
SiriusHardware
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Default Re: 1978 Commodore PET project

Quote:
Is there any way to verify the operation of the keyboard interface on the main board
In principle, yes, you can unplug the keyboard from the main PCB and use a wire link to join individual row and column pins of the mainboard keyboard connector to 'type' characters.

It makes more sense to do this when you can see what you are typing, so I would leave that stage until after the display section is working properly.
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Old 27th Sep 2022, 6:56 pm   #135
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Default Re: 1978 Commodore PET project

Back in the mid 80's I was a CBM authorized svc tech. for a CBM ASC.

I quickly learned to use only machine pin sockets, as they were mechanically & electrically better than the cheaper ones. (I hated callbacks).

If you really need a schematic, Howard W. Sams covered the 2 (USA) models of the CBM computers, and there is a slight possibility I may have OEM svc literature for the U.S. models still...maybe... That was 40+ years back.

Mostly they wanted us a board changers.

The highest failure item I ran across was the floppy drives failing.
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Old 27th Sep 2022, 7:23 pm   #136
ScottishColin
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Default Re: 1978 Commodore PET project

I have a dual disk drive 4040 that worked first time (well, after someone here helped me fix the power supply). I was somewhat surprised.

If you ever find those service manuals/literature, I'd love to see a copy (or even buy them off you if you're wanting to move them on).

Colin.

Quote:
Originally Posted by FrankB View Post
Back in the mid 80's I was a CBM authorized svc tech. for a CBM ASC.

I quickly learned to use only machine pin sockets, as they were mechanically & electrically better than the cheaper ones. (I hated callbacks).

If you really need a schematic, Howard W. Sams covered the 2 (USA) models of the CBM computers, and there is a slight possibility I may have OEM svc literature for the U.S. models still...maybe... That was 40+ years back.

Mostly they wanted us a board changers.

The highest failure item I ran across was the floppy drives failing.
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Old 27th Sep 2022, 8:24 pm   #137
BrackenFix
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Default Re: 1978 Commodore PET project

Pretty.....
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Old 27th Sep 2022, 8:42 pm   #138
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Default Re: 1978 Commodore PET project

I would have been glad if I'd looked as good as that when I was 40+ years old...
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Old 27th Sep 2022, 9:04 pm   #139
BrackenFix
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I actually said the same thing in my video
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Old 27th Sep 2022, 9:16 pm   #140
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Default Re: 1978 Commodore PET project

There’s one quick check that could be worth doing before getting to the de-soldering stage. Try running the machine with the socketed PIAs (UC6 and UC7) removed. Faulty PIAs are not uncommon and can cause display corruption. You don’t need to reconnect the keyboard to do this. An otherwise working PET will happily boot to BASIC without the PIAs although there won’t be a cursor and some of the interfaces won’t work.

Alan
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