9th Feb 2020, 2:00 pm | #41 |
Hexode
Join Date: May 2013
Location: Middlesbrough, North Yorkshire, UK.
Posts: 442
|
Re: Commodore PET 3016
|
9th Feb 2020, 2:06 pm | #42 |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,587
|
Re: Commodore PET 3016
Looking at your results so far, the measurements for the connections between the 6520 (dot) and the 74LS145 look OK and appear to confirm that in this detail at least, the circuit we have matches the circuit of your keyboard scanning circuit.
When reading the results for the connections between the IC pins and ground and between the IC pins and other IC pins on the same chip, look a bit more carefully at the meter display to see if it is actually indicating Ohms, KiloOhms or MegaOhms. For the IC pin to ground and IC pins to other IC pins on the same chip, I would expect you to be seeing typically KiloOhms or MegaOhms rather than Ohms. |
9th Feb 2020, 2:06 pm | #43 | |
Hexode
Join Date: May 2013
Location: Middlesbrough, North Yorkshire, UK.
Posts: 442
|
Re: Commodore PET 3016
Quote:
|
|
9th Feb 2020, 2:16 pm | #44 |
Hexode
Join Date: May 2013
Location: Middlesbrough, North Yorkshire, UK.
Posts: 442
|
Re: Commodore PET 3016
This is the setting I've used on the multimeter
|
9th Feb 2020, 2:23 pm | #45 |
Hexode
Join Date: May 2013
Location: Middlesbrough, North Yorkshire, UK.
Posts: 442
|
Re: Commodore PET 3016
Here are the Ground to 74145N readings using 20k setting on multimeter:
74LS145N 15 0V 4.30 20k setting 74LS145N 14 0V 4.45 20k setting 74LS145N 13 0V 4.32 20k setting 74LS145N 12 0V 4.40 20k setting |
9th Feb 2020, 3:04 pm | #46 |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,587
|
Re: Commodore PET 3016
OK, that's fine, and use the same multimeter setting for doing the checks between IC pins on the same IC. The main thing you are looking for is for there not to be a short (zero Ohms) between any of the pins on the same IC.
Can you clarify the situation with this fault? Has this machine had the fault since you obtained it? Originally you said you had tried replacing the large socketed ICs so we have been proceeding on the assumption that those ICs are ruled out. If you replace a chip with another chip and the fault does not change at all, there is a fair chance both ICs are identical, and either both are OK, or (if you are very unlucky) both are faulty in exactly the same way. However, if you replace a chip with another chip of the same type and that changes the fault from one set of symptoms to another, what that tells you is that there is a difference between the two allegedly identical ICs. Usually, this will mean that the second IC is faulty but, crucially, it does not prove that the original IC is NOT faulty. The first IC may have one fault: The second IC may have a different fault. Where there is doubt, the only way to settle the question is to try a third, known working IC from somewhere else. One thing you could possibly try is to (temporarily) swap the 'other' 6520 which is already in the machine with the 'dot' 6520, to see what happens then. |
9th Feb 2020, 3:49 pm | #47 |
Hexode
Join Date: May 2013
Location: Middlesbrough, North Yorkshire, UK.
Posts: 442
|
Re: Commodore PET 3016
Just as an exepriment I have replaced all the ICs with the ones that were in there when I got the machine. There is no difference at all. Does this mean that these chips work??
J |
9th Feb 2020, 3:52 pm | #48 |
Hexode
Join Date: May 2013
Location: Middlesbrough, North Yorkshire, UK.
Posts: 442
|
Re: Commodore PET 3016
Except that I've just noticed - in BASIC mode rather than BASIC 4, when I press:
QAZ I get the next line along WSX and WSX prodcues WSX - which I wasn't getting before! Everything else though is exactly the same. |
9th Feb 2020, 3:56 pm | #49 |
Hexode
Join Date: May 2013
Location: Middlesbrough, North Yorkshire, UK.
Posts: 442
|
Re: Commodore PET 3016
I've just swapped the 6520's around and again - not difference in the main except that when I press the SHIFT key I don't get anything from the QAZ or WSX as I did when it wasn't pressed.
|
9th Feb 2020, 4:21 pm | #50 |
Hexode
Join Date: May 2013
Location: Middlesbrough, North Yorkshire, UK.
Posts: 442
|
Re: Commodore PET 3016
Using 20k on multimeter This is what I got from both of the 'orginal' 6520's- I paired them below as you can see testing each IC separately. Most pairings return a value even if that was 1 except 37 with 38. This was the same in both ICs.
40 and 39 - 1 37 and 38 - 0.00 37 and 36 - 1 35 and 34 - 1 34 and 33 - 1 all the way down to 26-27 - 1 then 25-26 another value |
9th Feb 2020, 4:40 pm | #51 |
Hexode
Join Date: May 2013
Location: Middlesbrough, North Yorkshire, UK.
Posts: 442
|
Re: Commodore PET 3016
I changed the original 6520s and the 6522 with new ones. I am running the machine in BASIC 4 and the same issues arise as with all of the original ICs. I get exactly the same key return patterning as before. When SHIFT is depressed, only 0 . - and = characters on the number pad work and these return graphics with 0 and . returning the same ones and the - and = returning the same ones.
|
9th Feb 2020, 4:45 pm | #52 |
Hexode
Join Date: May 2013
Location: Middlesbrough, North Yorkshire, UK.
Posts: 442
|
Re: Commodore PET 3016
Running in BASIC 2 returns exactly the same thing except that pressing RUN/STOP button I can get the PET to load a game from the cassette which I can't if it's running BASIC 4.
|
9th Feb 2020, 4:46 pm | #53 |
Hexode
Join Date: May 2013
Location: Middlesbrough, North Yorkshire, UK.
Posts: 442
|
Re: Commodore PET 3016
Changing the 2 2114s alters nothing - I see no difference
|
9th Feb 2020, 4:50 pm | #54 |
Hexode
Join Date: May 2013
Location: Middlesbrough, North Yorkshire, UK.
Posts: 442
|
Re: Commodore PET 3016
I am wondering whether I shouldn't just put back all the original ICs
|
9th Feb 2020, 4:56 pm | #55 |
Hexode
Join Date: May 2013
Location: Middlesbrough, North Yorkshire, UK.
Posts: 442
|
Re: Commodore PET 3016
I'm going to be really cheeky and ask whether anyone close by would be willing to spend an hour or two with me to make sure I am doing these things right? I live near Middlesbrough and work in County Durham so travelling is not a problem for me!!
|
9th Feb 2020, 10:00 pm | #56 |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,587
|
Re: Commodore PET 3016
I think you need a bit more faith in your own ability.
Going by all the combinations of everything you've done, I am inclined to assume for now that the original socketed chips which were in the machine are probably OK. Which brings us, unfortunately, back to something you have not tried yet, the 74LS145 or its associated connections. I'm also happy with your findings on the input side of the 74LS145, connections from there to the 6520 are OK, the A/B/C/D input lines all show roughly the same resistance to 0V. I'm not sure whether you did the checks for possible shorts between pins 15,14,13,12 of the 74LS145. There's a bit more checking we can do on the output side of the 74LS145 before going to the next step of replacing it. It's a little bit late for me to get it all down here tonight, I'll try to outline some suggestions for you tomorrow. |
10th Feb 2020, 1:23 am | #57 |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,587
|
Re: Commodore PET 3016
Some further checks:
With the keyboard disconnected, power off as before and with your meter on its lowest ohms range check that the resistance between the following pairs of points is very low, at or near to zero ohms. 74LS145 Pin 1 to main board keyboard connector pin '1' 74LS145 Pin 2 to main board keyboard connector pin '2' 74LS145 Pin 3 to main board keyboard connector pin '3' 74LS145 Pin 4 to main board keyboard connector pin '4' 74LS145 Pin 5 to main board keyboard connector pin '5' 74LS145 Pin 6 to main board keyboard connector pin '6' 74LS145 Pin 7 to main board keyboard connector pin '7' 74LS145 Pin 9 to main board keyboard connector pin '8' * Note the IC pin number has jumped from 7 to 9 74LS145 pin 10 to main board keyboard connector pin '9' 74LS145 pin 11 to main board keyboard connector pin '10' Then with the black probe on 0V and the meter set initially to the 20K ohms range, measure the resistance from main board keyboard connector pins '1' through to '10' down to 0V and check that they all have a similar resistance. The actual resistance is not important, but all ten pins should read roughly the same resistance down to 0V. If you get an 'infinite' reading on them all, go up one ohms range higher and measure again. With the meter back down to the lowest ohms range, check the resistance between the following pairs of keyboard connector pins to make sure there are no shorts or very low resistances between any of these pairs of main board keyboard connector pins: 1 and 2 2 and 3 3 and 4 4 and 5 5 and 6 6 and 7 7 and 8 8 and 9 9 and 10 Finally, with the meter set to 20K ohms range and the red meter probe held on pin 16 of the 74LS145, measure the resistance from there to each of the main board keyboard connector pins 'A' through to 'J'. For this group of measurements you should see around 10K, perhaps a little less. |
10th Feb 2020, 10:15 pm | #58 | ||
Hexode
Join Date: May 2013
Location: Middlesbrough, North Yorkshire, UK.
Posts: 442
|
Re: Commodore PET 3016
Quote:
Quote:
Hope I've done this right!! I've bought a new 74LS145 just in case!! J |
||
10th Feb 2020, 11:13 pm | #59 |
Hexode
Join Date: May 2013
Location: Middlesbrough, North Yorkshire, UK.
Posts: 442
|
Re: Commodore PET 3016
I tested the video IC MOS 901447-10 on 2000k with the pairings - 1-2, 2-3 etc. Most gave a reading of 1 or about 780 etc however, pin pairings 21-20 = 003 - Is this significant? Not sure it is.
|
10th Feb 2020, 11:19 pm | #60 |
Hexode
Join Date: May 2013
Location: Middlesbrough, North Yorkshire, UK.
Posts: 442
|
Re: Commodore PET 3016
|