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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 6th Mar 2021, 8:56 pm   #821
ajgriff
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Default Re: Non-working Commodore PET 3016

First step is to identify which models they are and in particular which PCB assemblies are fitted. The attached service manual should help. I've got some other documentation which may be useful if you end up fault finding again. With any luck at least one of them might just work as it is. Worth scanning through the last few pages of the other PET thread.

Alan
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File Type: pdf C2N 1530 1531 Service Manual.pdf (1.66 MB, 15 views)
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Old 6th Mar 2021, 9:22 pm   #822
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Default Re: Non-working Commodore PET 3016

You can actually do some testing of a C2N without a working PET (or VIC20/C64) providing you can provide it with 5V power. This would enable the drive train to be tested. Basic read functionality can also be verified using a scope and a suitable tape recording. I can provide more detail if needed.

Alan
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Old 6th Mar 2021, 10:19 pm   #823
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Default Re: Non-working Commodore PET 3016

I forgot to mention that the most common problem with an old C2N is a perished drive belt but they can be found on the internet for a couple of pounds or so and are easy to fit.

In the absence of a signal generator I guess you could test rudimentary write functionality using the headphone output of a smart phone playing tones from a media player. Not something I've tried though.

Alan
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Old 6th Mar 2021, 10:27 pm   #824
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Default Re: Non-working Commodore PET 3016

I hesitate to pick up on the mention of CESIL...

https://twitter.com/DarkBlueMonkey/s...21060496429057

this thread is thrashing around like a fire hose with nobody holding it - idle hands and all that! Let's hope Cricklewood do not take too long...

...anyone remember Magenta? my diary for last week from 1981 said I had just had a delivery of 10 of parts from them to build a fuzz box for a mate which I was punting out for 15...
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Old 6th Mar 2021, 10:46 pm   #825
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Default Re: Non-working Commodore PET 3016

Yes, please, let's try to keep this one on the subject of the repairs to Colin's PET, it has already had to be tidied up once. I am sure there is enough interest in Commodore tape machines just now to support a new thread on that subject.
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Old 6th Mar 2021, 11:16 pm   #826
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Default Re: Non-working Commodore PET 3016

Quote:
Originally Posted by SiriusHardware View Post
Yes, please, let's try to keep this one on the subject of the repairs to Colin's PET, it has already had to be tidied up once. I am sure there is enough interest in Commodore tape machines just now to support a new thread on that subject.
He mentioned CESIL first though...
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Old 7th Mar 2021, 8:13 pm   #827
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Default Re: Non-working Commodore PET 3016

My fault.

back to the plot. I have spare sockets here now - I'll start with H6 and remove that/solder in the new socket; is that the right place to start?

Colin.
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Old 7th Mar 2021, 8:15 pm   #828
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Default Re: Non-working Commodore PET 3016

I've been following the thread with interest. But Colin's post about the origin of his interest in PETs means I have something to share.

I too first came to computing and PETs while at school. We also only had a dumb terminal linked via acoustic coupler to Milton Keynes and no pupils were allowed near it, in fact most staff weren't.

But my Dad worked at Lanchester Polytechnic who bought some of the first models, and as they finished for summer before schools, he was allowed to loan one to the school for the last two weeks of term, for 2 or 3 years.

After they had been in the poly a couple of years, the 'A' key started to wear out on most of them. Again reminded of this by the OPs reference to space invaders, where 'A' was the fire button. There was another game, Star Wars, where one had to do the bomb run and destroy the death star.

Good luck with getting it running, Colin. It's as much part of my history as it is yours.
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Old 7th Mar 2021, 9:20 pm   #829
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Default Re: Non-working Commodore PET 3016

Quote:
I'll start with H6 and remove that/solder in the new socket; is that the right place to start?
Certainly is.
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Old 7th Mar 2021, 9:43 pm   #830
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Default Re: Non-working Commodore PET 3016

Done.

Colin.


Quote:
Originally Posted by SiriusHardware View Post
Quote:
I'll start with H6 and remove that/solder in the new socket; is that the right place to start?
Certainly is.
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Old 8th Mar 2021, 6:39 pm   #831
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Default Re: Non-working Commodore PET 3016

To keep me entertained until tomorrow, is there any simple testing powered on or off I can do of the RAM chips while I await the replacement ICs?

Some of the legs look a little rusty so I am expecting problems there too....

Colin.
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Old 8th Mar 2021, 7:10 pm   #832
SiriusHardware
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Default Re: Non-working Commodore PET 3016

You can try (with power off) making resistance measurements from the following points to 0V and to +5V

UJ2 pins 5,7,6,12,11,10,13 (Lines FA0 to FA6).

Also from the following points to 0V and +5V,

UI10 pins 8/9, UI10 pins 6/7, UI10 pins 4/5, UI10 pins 2/3
UI11 pins 8/9, UI11 pins 6/7, UI11 pins 4/5, UI11 pins 2/3

As usual for this sort of measurement,
The measurements from the UJ2 pins to 0V should all be about the same,
The measurement from the UJ2 pins to +5V should all be about the same,
The measurement from the UI10 / UI11 pins to 0V should all be about the same
The measurement from the UI10/UI11 pins to +5V should all be about the same.

No need to report them all individually but if you see something which looks like an odd man out, let us know.

And with power on, check voltage on each of UJ2-UJ9 and UI2 to UI9,
Pin 8 = +12V
Pin 9 = +5V
Pin 1= -5V
Pin 16=0V.

When doing these voltage checks be exceptionally careful not to slip and short pin 8 (+12V) to nearby pin 7 on any of the ICs.
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Old 8th Mar 2021, 8:19 pm   #833
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Default Re: Non-working Commodore PET 3016

Couple of notes:

UI11 2 and 3 measure 0.61 (with the meter set to 2k) and the rest of the pins on UI11 0.71 to +5v. Is that significant? There's a similar drop when I measure to 0V.

All RAM chips pin 16 give me (c.) 0.25V

Apart from that seems OK. Some pins need a bit of scaping to give me a reading; I'll get them cleaned up.

Colin.




Quote:
Originally Posted by SiriusHardware View Post
You can try (with power off) making resistance measurements from the following points to 0V and to +5V

UJ2 pins 5,7,6,12,11,10,13 (Lines FA0 to FA6).

Also from the following points to 0V and +5V,

UI10 pins 8/9, UI10 pins 6/7, UI10 pins 4/5, UI10 pins 2/3
UI11 pins 8/9, UI11 pins 6/7, UI11 pins 4/5, UI11 pins 2/3

As usual for this sort of measurement,
The measurements from the UJ2 pins to 0V should all be about the same,
The measurement from the UJ2 pins to +5V should all be about the same,
The measurement from the UI10 / UI11 pins to 0V should all be about the same
The measurement from the UI10/UI11 pins to +5V should all be about the same.

No need to report them all individually but if you see something which looks like an odd man out, let us know.

And with power on, check voltage on each of UJ2-UJ9 and UI2 to UI9,
Pin 8 = +12V
Pin 9 = +5V
Pin 1= -5V
Pin 16=0V.

When doing these voltage checks be exceptionally careful not to slip and short pin 8 (+12V) to nearby pin 7 on any of the ICs.
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Old 8th Mar 2021, 8:35 pm   #834
SiriusHardware
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Default Re: Non-working Commodore PET 3016

A percentage of difference between one line and seven others which are theoretically identical to it could turn out to be significant, so we'll remember that anomaly for the future.

Each of those pairs of UI10 / UI11 pins is in turn connected to a pair of DI/DO pins on two of the 4116 RAMs, so you have a total of 6 IC pins connected to each of those circuit nodes. If you have one out of the 6 pins faulty and five normal, that could certainly shift the reading away from what is 'normal' on the other, similar nodes.

A quarter of a volt is quite a significant difference between your 'gold standard' 0V and the supposed 0V in that area of the circuit. With power off, can you measure the resistance between some of the RAM IC pin 16s and your usual 0V point? It should be very, very low.
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Old 8th Mar 2021, 8:48 pm   #835
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Default Re: Non-working Commodore PET 3016

Pin 16 on all RAM chips give me a 0.00 reading.

Colin.

Quote:
Originally Posted by SiriusHardware View Post
A percentage of difference between one line and seven others which are theoretically identical to it could turn out to be significant, so we'll remember that anomaly for the future.

Each of those pairs of UI10 / UI11 pins is in turn connected to a pair of DI/DO pins on two of the 4116 RAMs, so you have a total of 6 IC pins connected to each of those circuit nodes. If you have one out of the 6 pins faulty and five normal, that could certainly shift the reading away from what is 'normal' on the other, similar nodes.

A quarter of a volt is quite a significant difference between your 'gold standard' 0V and the supposed 0V in that area of the circuit. With power off, can you measure the resistance between some of the RAM IC pin 16s and your usual 0V point? It should be very, very low.
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Old 8th Mar 2021, 9:32 pm   #836
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Default Re: Non-working Commodore PET 3016

Quote:
All RAM chips pin 16 give me (c.) 0.25V
Apologies, I was responding to this (above) in your post #833. Did that change since then or did you maybe mean a different pin?
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Old 8th Mar 2021, 10:03 pm   #837
ScottishColin
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Default Re: Non-working Commodore PET 3016

The 0.25V on pin 16 is the reading with the power on. The 0.00Ω reading is resistance with power off.

Colin.
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Old 8th Mar 2021, 10:27 pm   #838
SiriusHardware
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Default Re: Non-working Commodore PET 3016

Ah, it's all a question of units. (Some day you'll have to explain to me how you get that 'Omega' character - I don't seem to have one on my keyboard).

You do occasionally get some apparently impossible or unlikely voltage readings. (If there really is zero ohms between those two points then there is no way for the voltages on them to be different, because they are directly connected together). Let's not worry about that for now. We should be able to make a bit more progress when your replacement UH6 etc. arrive.

With the new UH6 fitted look for activity on pins 2 and 3 of UH6, you should see 500KHz waveforms on both of those.

If you do have those, then look for activity on the outputs of UH9 pins 12, 9, 8, 11.

Let us know how that goes.
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Old 8th Mar 2021, 10:42 pm   #839
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Default Re: Non-working Commodore PET 3016

Hopefully they'll pop through the letterbox tomorrow.

Alt+234 gives the Omega sign btw. I've used alt for years to get different ASCII characters.

https://support.microsoft.com/en-us/...the%20keyboard.

Colin.
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Old 8th Mar 2021, 10:50 pm   #840
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Default Re: Non-working Commodore PET 3016

PETSCII has a kind of version of alt. I found this out about 40 years ago when I was checking for a space on a screen as CHR(32) and couldn't find it, even though it was there as clear as anything. Turned out I had actually typed shift+space instead which looked like a space but was actually a different character number in PETSCII (160).

Colin.
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