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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 13th Mar 2020, 11:41 pm   #181
SiriusHardware
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Default Re: Commodore PET 3016

Perhaps PsychMan could provide a link to an example of the exact one he recommended, if it can be done without breaking forum rules.
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Old 13th Mar 2020, 11:51 pm   #182
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Default Re: Commodore PET 3016

I’ve seen the ones he mentions on EBay. From China I think. Looks good.
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Old 15th Mar 2020, 8:25 pm   #183
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Default Re: Commodore PET 3016

Hi folks, here’s another question regarding the sound output.

I have, at last, got the sound working simply by attaching the piezo buzzer to GND (Pin N) and CB2 (Pin M). Although quiet, it works well!

Someone I’ve been speaking to mentioned using a set of PC speakers which have amplifiers in them - I already have a set of these which I use with my MAC. He mentioned putting in a relevant socket to do this but I’m not sure where to start. I really like the idea of doing that though. It seems quite an elegant solution. What do you think?
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Old 15th Mar 2020, 10:57 pm   #184
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Default Re: Commodore PET 3016

Thinking this through-wouldn’t it just be a matter of connecting the stereo female plug to the two wires from GND (pin N) to CB2 (pin M)?
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Old 16th Mar 2020, 1:02 pm   #185
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Default Re: Commodore PET 3016

Just putting the PET through some new games I've acquired. It's doing a strange thing again! Now there is no '!' or '-'. It wasn't giving a '0' but now it is. All of these things were working when I switched in on this morning.

I've switched it off, waiting for it to cool down and I will restart.

Also the video output 'bounced' and 'wobbled' a little this morning in an up and down motion like a small vibration for a few minutes. Once the PET 'warmed-up' it stabilised. Now this. I guess it's welcome to the Vintage Computing Club!
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Old 16th Mar 2020, 1:10 pm   #186
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Default Re: Commodore PET 3016

The reboot after a few minutes seems to have done the trick. I was also having great difficulty loading programs too - I guess the issues could have been linked if the machine wasn't loading zeros and other characters properly!
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Old 16th Mar 2020, 2:13 pm   #187
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Default Re: Commodore PET 3016

I hadn't noticed before but the SHIFT stopped working too. I switched the machine off for about 10 minutes and all seems to be working again.
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Old 16th Mar 2020, 7:14 pm   #188
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Default Re: Commodore PET 3016

Rather than post fault reports in real time which makes the thread rather fragmented and hard to follow, try to investigate in a more methodical fashion and gather as much information as you can first.

For example, the next time one of your keys stops working, as seems to happen from time to time, go around and check which other keys are not working. They may all prove to be in the same column or the same row, which would be a useful clue.
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Old 16th Mar 2020, 8:00 pm   #189
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Default Re: Commodore PET 3016

Quote:
Originally Posted by SiriusHardware View Post
Rather than post fault reports in real time which makes the thread rather fragmented and hard to follow, try to investigate in a more methodical fashion and gather as much information as you can first.

For example, the next time one of your keys stops working, as seems to happen from time to time, go around and check which other keys are not working. They may all prove to be in the same column or the same row, which would be a useful clue.
Sorry - I get carried away!
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Old 17th Mar 2020, 4:48 pm   #190
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Default Re: Commodore PET 3016

If you havent already, take at the 8-bit guys video on repairing a pet and take apart the keyboard and clean it carefully. Sounds to me like you have dirty contacts that are inyermittant. Even if tracks are broken they can be repaired usually with condductive paint. I'd post a link to the video but my phone wont let me because it insists on using the youtube app rather than the videos URL.
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Old 17th Mar 2020, 6:51 pm   #191
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Default Re: Commodore PET 3016

Thank you. The performance was solved by switching off the computer for 10 mins. It’s not just the keys, it was also refusing to load software. After the 10 min shut down it all worked again. Strange.
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Old 17th Mar 2020, 8:29 pm   #192
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Default Re: Commodore PET 3016

Quote:
Originally Posted by John Earland View Post
Thank you. The performance was solved by switching off the computer for 10 mins. It’s not just the keys, it was also refusing to load software. After the 10 min shut down it all worked again. Strange.
I remember when my dad bought our PET 2001-8 after we'd had it a few months it would hang up after being on for ten minutes or so, and would be OK if you switched it off for a while. We took it back to the supplier and they diagnosed it as a faulty PROM that went bad when it got hot - apparrently this were a common fault. They worked out which one by letting the fault develop, cooling one chip at a time with freezer spray and immediately resetting the conputer. When the right chip was cooled the fault went away for a while.
Although in later PETs they changed the PROMs to a different type they were still mask programmed PROMs so If all else fails this might be an idea if you can still get freezer spray!
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Old 17th Mar 2020, 11:49 pm   #193
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Default Re: Commodore PET 3016

What sort of EPROMS could directly replace the original PROMs? Looking at this circuit diagram fragment:-

http://www.zimmers.net/anonftp/pub/c...N/320349-4.gif

...which may or may not correspond to John's PET board, it would appear that the PROMs are 24-pin 4K types. (Address range of each PROM is x000 to xFFF, = 4096 bytes or 4K).

The common 2732 isn't a drop-in replacement as the diagram shows pin 21 (A11 on 2732) tied high, whereas it is a chip select on the original PROMs. Pin 18 on the original PROMs is A11, whereas pin 18 on the 2732 is _CE.

You could make an adaptor from two stacked 24-pin turned pin sockets with the interconnecting pins 21 and 18 cut, and with the pin 18 / pin 21 connections rerouted. (EPROM pin 21 (A11) to PCB pin 18 (A11) and EPROM pin 18 (_CE) to PCB pin 20 (_CE1). I would also leave the pin 20-pin 20 interconnect in place so that PCB _CE1 would activate EPROM _OE as well as EPROM _CE.

Given a set of 2732s programmed with the correct code and one adaptor, it would be possible to replace one PROM at a time and run the machine for a while each time to see if that made it stable. There may be directly pin compatible EPROM or EEPROM devices but I can't bring any to mind. They are likely to be rather rare and expensive compared to standard 27-series.

Another possibility is to write a programme which reads the checksum of the memory area of one PROM at a time, checksumming it continually. Note the 'normal' value which is being read most of the time but have the program stop and flag a warning if the checksum result changes away from the normal value at any time. Any such program would best be written in RAM-resident machine language so that it did not depend on the content of the PROMs to be able to keep running. It need not display output to the screen, either, something as simple as lighting a LED connected to a user port bit when a checksum error was detected would do.
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Old 17th Mar 2020, 11:59 pm   #194
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Default Re: Commodore PET 3016

Just looking further, the Motorola MCM68764 is a better drop in replacement as A11 is in the right place and pin 21 (held high on the PET PCB) is A12 - yes, it's an 8K part but if the 4K of PROM code were programmed into the upper half of the MCM68764, it would work.

This would probably be the neatest way to replace a known bad PROM, although those MCM68764s are not very cheap - typically around £15 or more each.
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Old 18th Mar 2020, 9:54 am   #195
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Default Re: Commodore PET 3016

I think this is above my capabilities! I do think it's worth looking at though - for the majority of the time everything seems to work fine. As it's over 40 years old I would expect some breakdown to occur now and then (or maybe I shouldn't!). It just seemed to stop loading programs then, after a 10 min pause, started fine again. I am working from home today so will put it through its paces to check how things are going and report back. Switched it on first thing and loaded 'Pinball' no problem.

I do get a slight wobble from the video output though, until things warm up (about 3-5 mins) - very slight. Then it settles. After a couple of hours continuous use, it comes back again from time to tme but only for a few seconds, then settles again.
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Old 6th Apr 2020, 5:00 pm   #196
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Default Re: Commodore PET 3016

Hi folks-I wonder if anyone has encountered an odd event when running software?
We’ve been playing Space Invaders on the PET -it’s great but... when the machine has been running a while, when you get to a certain point in the game, say you’ve almost completed a stage with only a few aliens to kill(!) the game restarts! It’s like a weird software glitch except that it doesn’t seem to occur when the machine is cold! Now it may be coincidence-but has anyone encountered anything like this? Is it likely to be a hardware issue. Here’s a question.. we’ve been playing Space Invaders on the PET -it’s great but... when the machine has been running a while when you get to a certain point the game it restarts! It’s like a weird glitch! Now it may be coincidence-it’s not a software thing ( I don’t think) because when the machine is cold we can progress through to the next round if you clear the first but when it’s been on a while the game resets and it’s like you’ve started again-all scores go back to zero. Has anyone encountered something like this?
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Old 6th Apr 2020, 5:36 pm   #197
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Default Re: Commodore PET 3016

I'm wondering if you have a thermal - intermittent RAM IC, such that the game code resident in RAM is OK while the machine is cold but starts to get corrupted, perhaps just a single bit in one byte, when the IC starts to warm up. Unfortunately detecting this with freezer spray won't work in the usual sense because once the fault happens and the software goes haywire, cooling the chip responsible won't restore the system to normal operation as it did your ZX81 ULA.

How many RAM ICs are there in the machine, what sort or RAMs are they, are they in sockets and do you have any spares?

Anyone who knows these machines, is there a RAM tester program available for these, one which can be set to run constantly until manually interrupted?

Last edited by SiriusHardware; 6th Apr 2020 at 5:53 pm.
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Old 6th Apr 2020, 5:37 pm   #198
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Default Re: Commodore PET 3016

I am using the Tynemouth Software hardware add on. This slots into the CPU slot and takes over the RAM and ROMs.
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Old 6th Apr 2020, 5:56 pm   #199
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Default Re: Commodore PET 3016

OK, is it possible that you can try running your invaders game using the original circuitry only, or does it not have enough RAM when configured that way?
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Old 6th Apr 2020, 7:54 pm   #200
John Earland
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Default Re: Commodore PET 3016

I don’t have the original ROMS-I could try to source them-there are four I believe.
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