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Old 27th Sep 2022, 10:19 pm   #141
ScottishColin
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Default Re: 1978 Commodore PET project

Wait until you open it up. This is what was inside my keyboard (although the closer keys of your keyboard may save you from this).

Colin.
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Old 28th Sep 2022, 1:49 pm   #142
BrackenFix
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Default Re: 1978 Commodore PET project

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Originally Posted by ajgriff View Post
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
Hello

I removed UC6 and UC7 and the screen was the same
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Old 28th Sep 2022, 1:57 pm   #143
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Default Re: 1978 Commodore PET project

Shows that the PIAs aren't causing the problem thus eliminating them from our enquiries at this stage. Worth doing as it's a quick and easy check.

Alan
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Old 28th Sep 2022, 2:32 pm   #144
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Default Re: 1978 Commodore PET project

Absolutely, took 2 minutes and that included 30 seconds trying to move the heavy lump
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Old 3rd Oct 2022, 11:37 am   #145
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Default Re: 1978 Commodore PET project

Sorry for the radio silence.

I have got the keyboard working now and the 3 replacement chips have arrived.

Just deciding the best way to swap the chips so will report back soon
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Old 3rd Oct 2022, 11:50 am   #146
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Default Re: 1978 Commodore PET project

Well done on the progress with the keyboard.

If in doubt, snip the legs off the original ICs high up next to the body of the chip, remove the body and then desolder and remove the individual pins. There are still plenty of chips around but you only have that one 40+ year old mainboard, so not damaging it is your main priority.

Suggested order of replacement was (I think) UE7, UF7, UF9 replacing only one at a time and trying the machine again after each chip change.
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Old 3rd Oct 2022, 12:04 pm   #147
ScottishColin
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Default Re: 1978 Commodore PET project

When I was at this stage, I carefully used a hobby 12v drill and a metal cutting disc to cut each leg off as high as I could. A careful hoover to suck up any metal shards was required to make sure I had left nothing to short anything else. This seemed (to me) to exert less pressure on the pads on the motherboard than snipping each leg.

I guess we all have our own ways....

Colin.


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Well done on the progress with the keyboard.

If in doubt, snip the legs off the original ICs high up next to the body of the chip, remove the body and then desolder and remove the individual pins. There are still plenty of chips around but you only have that one 40+ year old mainboard, so not damaging it is your main priority.

Suggested order of replacement was (I think) UE7, UF7, UF9 replacing only one at a time and trying the machine again after each chip change.
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Old 3rd Oct 2022, 12:20 pm   #148
ScottishColin
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Default Re: 1978 Commodore PET project

Nice video.

https://www.youtube.com/watch?v=gs85-hyFhI0

Colin.
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Old 3rd Oct 2022, 12:36 pm   #149
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Thank you. Was very happy it all worked out.

Using paper was a great tip
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Old 3rd Oct 2022, 12:52 pm   #150
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Default Re: 1978 Commodore PET project

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When I was at this stage, I carefully used a hobby 12v drill and a metal cutting disc to cut each leg off as high as I could
The potential to shed fine metal dust far and wide is exactly why I wouldn't normally suggest doing it that way.

As for exerting force on the pads while trying to cut the legs, that's why the advice is to cut them high up, not low down next to the PCB.

Most electrical / electronics side cutters are too clunky and the ends of the jaws too thick and blunt to slip into the gap on either side of an IC pin, that's why I keep mentioning 'cuticle nippers' which are essentially a miniature version of the same thing.
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Old 3rd Oct 2022, 12:56 pm   #151
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Default Re: 1978 Commodore PET project

I am certainly no expert on this, but it worked for me and seems to be the least abrasive to start off with.

Colin.


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Quote:
Originally Posted by ScottishColin View Post
Thank you. Was very happy it all worked out.

Using paper was a great tip
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Old 3rd Oct 2022, 12:56 pm   #152
ScottishColin
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Default Re: 1978 Commodore PET project

I got lucky then.

Colin.


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Quote:
When I was at this stage, I carefully used a hobby 12v drill and a metal cutting disc to cut each leg off as high as I could
The potential to shed fine metal dust far and wide is exactly why I wouldn't normally suggest doing it that way.

As for exerting force on the pads while trying to cut the legs, that's why the advice is to cut them high up, not low down next to the PCB.

Most electrical / electronics side cutters are too clunky and the ends of the jaws too thick and blunt to slip into the gap on either side of an IC pin, that's why I keep mentioning 'cuticle nippers' which are essentially a miniature version of the same thing.
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Old 3rd Oct 2022, 1:26 pm   #153
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Default Re: 1978 Commodore PET project

Quote:
I got lucky then.
As you so often do

On a more serious note the use of a rotary tool also poses the risk of generating static as well, I honestly would not do it that way myself.
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Old 3rd Oct 2022, 1:48 pm   #154
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Default Re: 1978 Commodore PET project

Will just be such a shame to damage the old chips. Granted they are possibly broken anyway but still a shame.

Leave it with me, I'll have a ponder
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Old 3rd Oct 2022, 1:49 pm   #155
ScottishColin
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Default Re: 1978 Commodore PET project

Got it. Thanks - I've learnt something more today.

Colin.


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Quote:
I got lucky then.
As you so often do

On a more serious note the use of a rotary tool also poses the risk of generating static as well, I honestly would not do it that way myself.
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Old 3rd Oct 2022, 2:26 pm   #156
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Default Re: 1978 Commodore PET project

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Will just be such a shame to damage the old chips
We always feel that way and we usually try harder to narrow it down to one device when it is possible to do so with the diagnostic tools and skill set available.

As you currently don't seem confident about removing ICs in one piece, your choices would seem to be, wait until you do feel confident (maybe when you've had a bit more practice with your desoldering gun) or play it safe and cut up one or two possibly blameless ICs in order to not damage the PCB.

You don't actually have to make that decision now, sleep on it for a week or a month if need be.
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Old 3rd Oct 2022, 2:52 pm   #157
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Default Re: 1978 Commodore PET project

What about the de-soldering tool?

Good work on the keyboard. Well done.

Alan
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Old 3rd Oct 2022, 2:59 pm   #158
BrackenFix
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Default Re: 1978 Commodore PET project

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What about the de-soldering tool?

Good work on the keyboard. Well done.

Alan
Desoldering tool is...delayed due to me spending the money on something else
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Old 3rd Oct 2022, 3:02 pm   #159
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Default Re: 1978 Commodore PET project

I have loads of tapes for when I can test them at least

Including one called Cosmic Jailbreak (proper Commodore one)
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Old 3rd Oct 2022, 5:43 pm   #160
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Default Re: 1978 Commodore PET project

I remember back when I was doing mobile phone repairs (19 years ago!!) we had a special soldering iron for replacing solder on ribbon cables, specifically the ones on Nokia 7650’s, it was a Metcal thing that had 2 elements which went into a single inch and a half long wedge shaped tip, I think one of those, or even 2 of them would make removing IC’s intact a lot easier.

Regards
Lloyd
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