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Old 5th Mar 2020, 9:27 pm   #141
John Earland
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Default Re: Commodore PET 3016

Hi - Thank you for that. I will test the voltage and check the resistor values - although it's not the speaker side I'm pretty sure.

Yes - the sound was working really well - albeit it quiet - from a simple piezo. I was testing a game then the picture went funny for a few seconds and I had to restart the machine. Then when I tried it again, the sound was 'damaged' - it sometimes works (but very quiet now) and tends to fade in and out. It also has a background hum/buzz when it does work. I'm using the amplifier kit you mentioned in a previous post - was really easy to put together.

With rergards to saving the BASIC program - I wrote a really simple one which I saved. Previously I was able to reload the program. It didn't run automatically - that's fine; I didn't expect it to. But at least I could save and load programs. Now, it won't save and I can't load the ones I did save. Though, it does load the pre-recorded ones and they seem to be bahving themselves.

On a positive, I kept the PET on for many hours today and part from that one issue with Space Invaders, it's performed really well. Video a little wobbly from time to time but nothing major.

John
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Old 5th Mar 2020, 9:55 pm   #142
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Default Re: Commodore PET 3016

Taking things in reverse, the wobbly video, if that has been consistent all the time, is possibly due to tired capacitors in the power supply / monitor circuit. That may also be why the machine does not always seem to start, if the power supply is only just able to handle the inrush at switch-on. Next time that happens, don't change anything around (as you did the 6520 this time) - instead leave it off for 2-3 minutes and then turn it on again and see if it starts.

If you had a an oscilloscope I would ask you to look at the supply rails, the +5V especially, to see how stable it is and whether it staggers a bit at switch-on. Refurbishment of the PSU is something which could go badly wrong if not done properly, if you want to look at that you may have to go back to your friendly technician again.

Saving to / loading from cassette - from the diagram it looks as though the machine has two ports for connection of a cassette unit, I can only guess that the unit can be plugged into either of those two ports and you have to refer to them at the command line as tape 0 / 1 or some other syntax to tell the machine which cassette port you are using.

Whichever port you normally have the cassette unit plugged into, try plugging it into the other one and see if it will (a) load something you already saved and (b) save and load something via that port.

Of the amplifiers I mentioned, which one did you eventually go for and is the sound broken with the simple sounder, the active amplifier or both? Which of the amplifiers did you go for in the end, the kit which included a speaker?

What are you using as the power supply for the amplifier, a battery, or are you taking the power from inside the computer somewhere?
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Old 5th Mar 2020, 10:57 pm   #143
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Default Re: Commodore PET 3016

About the tape saving problem - I assume these are normal sized audio cassettes.

Can you try writing and saving a program onto a tape which has never been used, in other words a tape which has nothing recorded on it?

Alternatively, make an 'empty' tape by putting a (non important) tape into an audio cassette recorder and recording nothing (no sound) onto it for about 5-10 minutes. (If using a hi-fi type cassette deck, turn the record level control down to zero). Then rewind the tape to the start of the 'silent' section, put it back in the computer cassette unit, save a programme onto the tape there and then try reloading it.

Why would I be asking you to do this? I'm wondering if the erase head / erase circuit in the computer's tape unit is not working. In those circumstances, saving to / loading from a tape would work if the tape was originally empty, but if you saved onto a tape which already had something on it, then you would have a mixture of saved program and other sounds from which the computer would not be able to pick out the program on replay.

If the cassette unit is as simple as Tony implied the 'erase head' may even be an actual magnet which is lowered onto the tape just ahead of the record / play head.

If the tape unit recorded audio onto the tape as the vast majority of home computers did, you would be able to listen to the tape in an audio cassette player to see what the recorded programme sounded like. You could still do that, but whatever gets recorded may sound rather strange.
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Old 6th Mar 2020, 10:17 am   #144
John Earland
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Default Re: Commodore PET 3016

Hi everyone, I'm at work today so will try all these things a little later. I never thought of using the second cassette port! Yes of course - why didn't I think of that? I will go through your comments methodically and post the results - thank you once again.
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Old 6th Mar 2020, 7:02 pm   #145
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Default Re: Commodore PET 3016

You can find circuit diagrams for various versions of the cassette recorder here :

http://www.zimmers.net/anonftp/pub/c...tte/index.html

The first manual on that list seems to be all you need. It appears there is a real erase head (not a permanent magnet) but it is simply fed with DC in record mode.
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Old 6th Mar 2020, 7:49 pm   #146
John Earland
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Default Re: Commodore PET 3016

Quote:
Originally Posted by SiriusHardware View Post
Earlier you said that a program which you had written, presumably in BASIC, and saved, and then loaded back in did not automatically run, although other software which you had did automatically run.

This behaviour would be my default assumption, on most computers of that age if you saved a BASIC program and then loaded it back in it would take you to the program listing, and you'd have to RUN it to make it do something. Commercially written software provided on tape is likely to be machine code and will usually be configured to start automatically once loaded.

However, my knowledge of how to actually use a PET is near zero, so I think you'll need to enlist the help of someone who knows these machines better in that respect.

It's probably worth checking the supply voltages now (with power on, and your meter on volts of course). For example, what voltage do you have (with respect to 0V) on pin 16 of the 74LS145? I'm assuming your meter volts range goes up in steps of 2V / 20V / 200V, if so use the '20V' range for this measurement. Only check the low voltages please, don't go anywhere near the mains side voltages unless you are absolutely confident that you know what you are doing.

With regard to the sound problem, what are your symptoms again? It was working to your satisfaction and then something happened, and now the sound is not what it was? What value of series resistor are you now using with the sounder? If you ever used the sounder in an Arduino project, does it still work with that Arduino project?

Space Invaders and demo mode: Unfortunately I'm not familiar with this software but the 'demo mode' was often provided so that the machine could be left running in 'attract mode' in a shop. It may not have encouraged anyone who took an interest to start playing on it (Expensive machine: Keys easily broken).
Hi -I tested the volts from the -ve (0V) of the large capacitor to pin 16 as above - it read 5.10v (at 20v setting)
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Old 6th Mar 2020, 7:52 pm   #147
John Earland
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Default Re: Commodore PET 3016

Quote:
Originally Posted by TonyDuell View Post
You can find circuit diagrams for various versions of the cassette recorder here :

http://www.zimmers.net/anonftp/pub/c...tte/index.html

The first manual on that list seems to be all you need. It appears there is a real erase head (not a permanent magnet) but it is simply fed with DC in record mode.
Thanks Tony - that's really helpful. I've just switched the machine on - no issues - started up well. wrote a 6 line BASIC program, saved it then verifyied it - no problems!!!
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Old 6th Mar 2020, 7:59 pm   #148
John Earland
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Default Re: Commodore PET 3016

I've just tried this too with the second cassette and it worked too!
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Old 6th Mar 2020, 8:02 pm   #149
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Default Re: Commodore PET 3016

Same issue though with a previous saving (before the new sockets). When I load this in via the 2nd cassette that too causes the PET to freeze at READY.
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Old 6th Mar 2020, 8:20 pm   #150
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Default Re: Commodore PET 3016

The sound amplifier and speaker I am using is the Kitronik one you mentioned. Very simple to put together following the instructions meticulously. It has two resistors; 15k and 100k
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Old 6th Mar 2020, 8:23 pm   #151
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Default Re: Commodore PET 3016

It sounds as though that particular recording may have become corrupt, unfortunately - not what you want to hear if it was a 150 line basic program typed in from a magazine.

The main thing is whether it continues to save and load consistently from now onwards - before the new sockets were fitted the machine couldn't really be relied upon to do the same thing the same way twice.

5.10V sounds nice - better to be slightly on the high side than half a volt low. Measuring with a meter doesn't really tell you how stable the supply is, though, you'd really need a scope, ideally a storage scope to capture how the 5V rail behaves for the first fraction of a second after switch-on.

Keep using it for a while and see how it behaves. I'll catch up with you later regarding the sound problem.
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Old 6th Mar 2020, 8:30 pm   #152
John Earland
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Default Re: Commodore PET 3016

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Originally Posted by SiriusHardware View Post
It sounds as though that particular recording may have become corrupt, unfortunately - not what you want to hear if it was a 150 line basic program typed in from a magazine.

The main thing is whether it continues to save and load consistently from now onwards - before the new sockets were fitted the machine couldn't really be relied upon to do the same thing the same way twice.

5.10V sounds nice - better to be slightly on the high side than half a volt low. Measuring with a meter doesn't really tell you how stable the supply is, though, you'd really need a scope, ideally a storage scope to capture how the 5V rail behaves for the first fraction of a second after switch-on.

Keep using it for a while and see how it behaves. I'll catch up with you later regarding the sound problem.
Thank you for that. Yes - it seems stable for now. Thanks great - no I write short programs just few lines for something to save.

Could there be damaged ceramic capacitors? thanks for the continued help. I really appreciate it.
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Old 7th Mar 2020, 12:45 am   #153
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Default Re: Commodore PET 3016

Just grabbing a spare moment here..

OK on the Kitronics amplifier - can you explain to me exactly how you have that connected in terms of connections to the PET and connections to power?

The kit comes with an audio input lead terminated with a 3.5mm stereo jack plug, which obviously can't be plugged into the PET directly - so how have you connected the amplifier to the PET?

If it's running on a battery pack or a clip full of batteries, what voltage are you getting from the battery pack (a) when the battery is not connected to the amplifier and (b) when it is connected to the amplifier?

Ceramic capacitors are not the highest things on my list to go looking for, but they can go short-circuit. In electronics of this age the more likely suspects are tired electrolytic capacitors - they are essentially like miniature batteries with wet stuff - electrolyte - inside, and if the electrolyte either leaks out or dries up then the operation of the capacitor is compromised.

There is a bit of a craze for 'recapping' - changing all the electrolytics in equipment of a certain age, but my preference is to replace only when necessary, especially in vintage equipment where it is desirable for the equipment to remain as unaltered and original as possible.

Last edited by SiriusHardware; 7th Mar 2020 at 12:55 am.
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Old 7th Mar 2020, 7:45 am   #154
John Earland
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Default Re: Commodore PET 3016

Quote:
Originally Posted by SiriusHardware View Post
Just grabbing a spare moment here..

OK on the Kitronics amplifier - can you explain to me exactly how you have that connected in terms of connections to the PET and connections to power?

The kit comes with an audio input lead terminated with a 3.5mm stereo jack plug, which obviously can't be plugged into the PET directly - so how have you connected the amplifier to the PET?

If it's running on a battery pack or a clip full of batteries, what voltage are you getting from the battery pack (a) when the battery is not connected to the amplifier and (b) when it is connected to the amplifier?

Ceramic capacitors are not the highest things on my list to go looking for, but they can go short-circuit. In electronics of this age the more likely suspects are tired electrolytic capacitors - they are essentially like miniature batteries with wet stuff - electrolyte - inside, and if the electrolyte either leaks out or dries up then the operation of the capacitor is compromised.

There is a bit of a craze for 'recapping' - changing all the electrolytics in equipment of a certain age, but my preference is to replace only when necessary, especially in vintage equipment where it is desirable for the equipment to remain as unaltered and original as possible.
For the sound: I connected the amplifier to the PET by linking the Black lead to the Earth (N) pin on the user port and the Red lead to CB2 (M).

For power: I connected the Earth lead to the Earth terminal on the PET Cassette port (A) and the Live lead to the 5v pin (B) on the cassette port.

For both of these I followed the instructions on the Zimmerman website. I've tested the output from B. I set the multimeter to 20v, put the black lead on the 0V of the large capacitor and put the red lead on B. It gave 5.10v.

Last edited by John Earland; 7th Mar 2020 at 7:56 am.
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Old 7th Mar 2020, 1:00 pm   #155
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Default Re: Commodore PET 3016

Yes, that all sounds good (no pun intended).

I think we first need to verify that the amplifier has not suffered some kind of damage.

If you still have the jack plug lead which came with the amplifier kit, temporarily disconnect the input wiring from the PET, connect the supplied 3.5mm input jack to the input of the amplifier and then plug it into any portable audio player you have handy (MP3 player, mobile phone) which has that sort of headphone socket and check that the amplifier / speaker sounds OK when driven from another source, but powered from the PET.

If it doesn't sound right, try powering the amplifier from the battery clip which was supplied in the kit and test the amplifier again using the alternative audio source.

To avoid possible complications when doing the first test (with the amplifier powered from the PET) the audio player you choose should be self contained / battery powered.
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Old 7th Mar 2020, 1:09 pm   #156
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Default Re: Commodore PET 3016

Just to check on terminology, by 'live' lead you mean the positive supply lead and by 'earth' lead you mean the negative supply lead?

The only reason I'm asking is that red and black (which you seem have used for the audio input) are much more traditionally used for power connections. If I was choosing the colours for audio input wiring myself I would probably choose any colour but red for the audio signal input wire, because otherwise it creates the possibility that someone will mistake the audio input connections for the power connections.
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Old 8th Mar 2020, 7:28 pm   #157
John Earland
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Default Re: Commodore PET 3016

Quote:
Originally Posted by SiriusHardware View Post
Just to check on terminology, by 'live' lead you mean the positive supply lead and by 'earth' lead you mean the negative supply lead?

The only reason I'm asking is that red and black (which you seem have used for the audio input) are much more traditionally used for power connections. If I was choosing the colours for audio input wiring myself I would probably choose any colour but red for the audio signal input wire, because otherwise it creates the possibility that someone will mistake the audio input connections for the power connections.
That's a really good point and I hadn't thought of that!!! I can easily change them and I think I will. Yes - Red = positive lead and Black = Negative. I will try out your suggestion and get back to you asap.
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Old 9th Mar 2020, 10:45 am   #158
John Earland
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Default Re: Commodore PET 3016

Right okay. I did a load of tests yesterday and thank you for your suggestions.

The speaker works perfectly. The fault lies in the amplifier. So either some of the components are faulty or my sodlering and construction is wrong - very likely!

I attached the speaker from the kit directly to the PET via Ground and CB2 and it worked - although quiet of course, sound was definitately being produced.

I tried this approach on a small piezo speaker and it's working perfectly! I don't know how or why but I'm not questioning it - yet!!

So, I will dismantle the amplifier and start again. When I tried the amplifier via a self contained mp3 player there was a lot of background buzz and the sound was intermittent. So it's obviously something I got wrong.

However, for the moment at least, I am able to load programs, save them and load them, and hear sound! So I am very happy!!
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Old 9th Mar 2020, 11:35 am   #159
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Default Re: Commodore PET 3016

Did the amplifier ever work?

You may have been unlucky enough to damage the IC on the amplifier, unfortunately - given that the cost of the entire kit is £3+, I would be surprised if you could buy a replacement IC more cheaply, and I don't think you would relish the prospect of trying to change that tiddly little surface mount IC.

If you can post a picture of the amplifer with all its wiring attached, views of both sides, we might be able to spot the problem.

You mentioned that when you tried the amp with a self contained player it didn't work well - was that also the case when the amplifier was independently powered (not powered from the PET)?
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Old 9th Mar 2020, 11:59 am   #160
John Earland
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Default Re: Commodore PET 3016

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Did the amplifier ever work?

You may have been unlucky enough to damage the IC on the amplifier, unfortunately - given that the cost of the entire kit is £3+, I would be surprised if you could buy a replacement IC more cheaply, and I don't think you would relish the prospect of trying to change that tiddly little surface mount IC.

If you can post a picture of the amplifer with all its wiring attached, views of both sides, we might be able to spot the problem.

You mentioned that when you tried the amp with a self contained player it didn't work well - was that also the case when the amplifier was independently powered (not powered from the PET)?
I don't think I would even attempt replacing that tiny IC - eek! Horror! Yes, the exact same response when powered from the PET and via the 2 AA batteries. I've uploaded some photos - please ignore the terrible blue colour of the negative lead!
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