22nd Jan 2021, 8:43 pm | #221 | |
Nonode
Join Date: May 2004
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Re: Non-working Commodore PET 3016
Quote:
I agree that there's no need for Colin consider this at this stage. Alan |
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22nd Jan 2021, 9:18 pm | #222 | ||
Octode
Join Date: May 2012
Location: Perth, Scotland
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Re: Non-working Commodore PET 3016
Quote:
2, 7, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 22, 23, 24, 25 Thanks. Colin. |
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22nd Jan 2021, 9:57 pm | #223 | |
Octode
Join Date: May 2012
Location: Perth, Scotland
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Re: Non-working Commodore PET 3016
Quote:
Note the switch on the probe on the scope is set to x1. It has a x10 option but I'm not really sure what that does. I was really happy enough to be able to get the scope working at all.... https://drive.google.com/file/d/1jvO...ew?usp=sharing |
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22nd Jan 2021, 11:07 pm | #224 |
Dekatron
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Re: Non-working Commodore PET 3016
The second capture of three - from UG5 pin 7 I gather, although the text got displaced a bit - shows a reasonable 1Mhz signal, a bit rounded but it is there. There is a way you can probably get that to look more 'square' but we'll come to that shortly.
Can you now have a look on at least pins 9, 10, and 11 of the CPU to see what you get there, plus any additional pins which Mark suggested?? |
23rd Jan 2021, 4:36 am | #225 |
Octode
Join Date: Mar 2020
Location: Kitchener, Ontario, Canada
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Re: Non-working Commodore PET 3016
I think pin 37, 39, 3, 2, 7, 9, 10, 11.
Should be enough to confirm 6502 is getting clock, but not running. |
23rd Jan 2021, 11:57 am | #226 | |
Nonode
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Re: Non-working Commodore PET 3016
Quote:
Alan |
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23rd Jan 2021, 12:38 pm | #227 | |
Octode
Join Date: Mar 2019
Location: Barry, Vale of Glamorgan, Wales, UK.
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Re: Non-working Commodore PET 3016
Quote:
That comes at a cost of sensitivity of course but, usually not a problem with modern scopes and the fact their displays will auto adjust when you select x10 option will help so you don't keep misreading values forgetting to multiply them by 10. It would not hurt to just always use x10 at these signal levels but, make sure you adjust the probe with the reference signal for a nice square wave as in your setup instructions. There is usually a little screw near the BNC connector. |
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23rd Jan 2021, 12:56 pm | #228 |
Dekatron
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Re: Non-working Commodore PET 3016
Yes, that was what I was referring to in #224 when I said the waveform could be made to look tidier. The frequency compensation trimmer is sometimes in the body of the probe rather than in the BNC plug. It would also be useful to switch channel 2 off so that channel 1 can use the whole height of the display.
I've been in the loft this morning and unfortunately could not find what I was looking for, a smallish microprocessor PCB which I know for sure has a Rockwell 6502 on it. As it's not where I was absolutely sure it was, I don't think I'll be able to find it in any reasonable time frame. I did find some NOS Z80 CTC (Counter-Timer) ICs though - anyone need one? Let's see what Colin finds on those signal lines, and hopefully we can say whether the existing 6502 is OK or not. |
23rd Jan 2021, 11:55 pm | #229 | |
Octode
Join Date: May 2012
Location: Perth, Scotland
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Re: Non-working Commodore PET 3016
Quote:
I have had to use the chassis as earth as the earth wire on the probe is not long enough to go to C62 from the 6502. I have included the frequency that the scope has detected at the bottom of each screenshot. https://drive.google.com/file/d/1Bdt...ew?usp=sharing |
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23rd Jan 2021, 11:56 pm | #230 | ||
Octode
Join Date: May 2012
Location: Perth, Scotland
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Re: Non-working Commodore PET 3016
Quote:
Sorry for the dumb question. Thanks. Colin. |
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24th Jan 2021, 12:00 am | #231 |
Octode
Join Date: Mar 2019
Location: Barry, Vale of Glamorgan, Wales, UK.
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Re: Non-working Commodore PET 3016
Nothing is dumb - just do it once or if you change from x1 to x10 settings as it calibrates the probes. You would also need to do it again if you bought new probes - also try to use the same probes on each port as the trim will be different for each port. This means you match a probe to a port
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24th Jan 2021, 12:06 am | #232 |
Octode
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Location: Barry, Vale of Glamorgan, Wales, UK.
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Re: Non-working Commodore PET 3016
Did you notice that on the scope screen there is a setting that allows you to say if the probe is in X1 or X10 switch position - this will mean that the displays read correctly - in your document to ensure we are reading the values correctly can you confirm that option was set by you - if not we will just adjust the values manually when looking.
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24th Jan 2021, 1:06 am | #233 |
Dekatron
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Re: Non-working Commodore PET 3016
I think we had better be specific. If possible Colin, try making all measurements from now on with the following parameters set:
With no signal present, adjust the vertical position of the scope trace line (the 'Y Position') so that it sits on the second faint line counting upwards from the bottom. This will be our 'zero volts'. I don't see an actual 'Y position' control such as there would be on a real scope but I think maybe you can click and drag the yellow '1' tab at the left hand side? If you can choose between 'DC' / 'AC' / 'GND' for the input mode choose 'DC'. On the probe: select x10 On the scope 'Front Panel' - select "x10" Set Channel 1 'Y' sensitivity: 1V / Div. (One Volt per division) Turn channel 2 off. With all of the above set, go to UG5 pin 7 where you have a known 1MHz signal and while looking at that, adjust the trimmer on the probe body or BNC plug for the squarest looking signal. Usually, you get a plastic trimming tool with the probe intended for that exact purpose. The setting of the 'horizontal' control will vary with the frequency of the signal you are trying to look at. For now, just get into the habit of adjusting it up or down until you can see around 5 or 10 cycles (ups and downs) of the signal you are trying to look at. I understand that the negative leg of C61 isn't always conveniently close to where you want to make measurements. With the power off, use your meter to check for continuity between that component leg and the chassis. If the resistance is less than 1 ohm then it is OK to use the chassis as the scope ground provided the point you choose on the chassis is clean and not painted - the ground lead of the probe must have good electrical contact to circuit 0V. |
24th Jan 2021, 1:27 am | #234 |
Dekatron
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Re: Non-working Commodore PET 3016
Looking back at the readings you collected, especially from pins 7, 9, 10, 11 - although the clock signal is reaching the CPU and passing through it, the CPU seems very inactive. If you can, please just verify (with a meter, with power on) that pin 40, Reset, is still at +5V.
Apart from that, anything else we can go at before we have to suspect the CPU? Mark? |
24th Jan 2021, 1:53 am | #235 |
Dekatron
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Re: Non-working Commodore PET 3016
I guess we had better check for +Ve supply to the CPU since it seems so dead, so Colin, as well as re-checking the voltage on pin 40 (reset) could you also look at the voltage on pin 8 (should be +5V). Although the clock is getting through from one side to the other, that might happen even if the IC was not powered. I'm thinking possible bad socket contacts or missing supply due to damage by damp / corrosion.
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24th Jan 2021, 2:55 am | #236 | |
Octode
Join Date: Mar 2020
Location: Kitchener, Ontario, Canada
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Re: Non-working Commodore PET 3016
Quote:
For the scope settings I would suggest starting with 500ns per division and widen out to about 5us per division. If you don’t see a trace on the scope try adjusting the trigger level, ;keep it on auto might be easiest. Did the pet have more than one 5v supply? Some of the older systems needed too much current for a single regulator. |
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24th Jan 2021, 9:49 am | #237 |
Dekatron
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Re: Non-working Commodore PET 3016
At it happens, there are two +5V supplies, although both were verified as being present at the regulators during early checks. The supply rails are the thickest tracks on the PCB so they are unlikely to have been corroded through, but individual pins could have corroded away where they meet the PCB surface if there has been standing moisture / dew on the PCB.
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24th Jan 2021, 1:54 pm | #238 |
Nonode
Join Date: Jan 2009
Location: Bristol, UK.
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Re: Non-working Commodore PET 3016
I have some UMC6502A's in my stash, these are NMOS according to the details I can find. Are these likely to work in the PET ?
dc |
24th Jan 2021, 2:27 pm | #239 |
Dekatron
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Location: Newcastle, Tyne and Wear, UK.
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Re: Non-working Commodore PET 3016
Quite possibly Dave, so we'll keep you in mind if that is OK. Still trying to establish whether the original 6502 is doomed or not.
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24th Jan 2021, 2:34 pm | #240 |
Nonode
Join Date: Jan 2009
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Re: Non-working Commodore PET 3016
No problem, PM me if required.
ATB |