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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 20th Jul 2023, 12:47 pm   #221
ScottishColin
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Default Re: Commodore PET 4032/8050/3022

OK - one reading at a time.

ROM pins 20 - I get readings on all ROM chips with the exception of UD10 - that just goes high and stays there.

Colin.
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Old 20th Jul 2023, 12:56 pm   #222
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Default Re: Commodore PET 4032/8050/3022

re the below - all present and correct.

"Another humdrum task, check the A0-A11 pins (Pins 8, 7, 6, 4, 3, 2, 1, 23, 22, 19, 18, in that order), on all of the main ROMs for the same frequencies you saw on the AB0-AB11 (CPU) address lines and the BA0-BA11 (Buffered) address lines."

Colin.
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Old 20th Jul 2023, 12:58 pm   #223
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Default Re: Commodore PET 4032/8050/3022

Pin 21 of all ROMs sitting at 5.33V.

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Old 20th Jul 2023, 1:01 pm   #224
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Default Re: Commodore PET 4032/8050/3022

With regard to the below, I have waveforms on all the mentioned pins.

"Then check the chip select signals on the large ICs - UB16 pins 22, 23, 24 (should all be active) UB15 pins 23, 24 (should be active), UB2 pins 22, 23, 24 (should all be active), UB13 pin 25 (should be active)."

Colin.
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Old 20th Jul 2023, 1:01 pm   #225
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Default Re: Commodore PET 4032/8050/3022

Quote:
I get readings on all ROM chips with the exception of UD10 - that just goes high and stays there.
UD10 is one of the three BASIC 4 ROMS so it should be getting enabled periodically by the NOP generator. Its chip select comes directly from UE12 pin 13 (SEL B). Check again for a mainly high, momentarily low chip select pulse coming out of UE12 pin 13 and if you still have that, check continuity between UE12 pin 13 and UD10 pin 20.
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Old 20th Jul 2023, 1:05 pm   #226
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Default Re: Commodore PET 4032/8050/3022

I have waveforms on all the below with the exceptionn of UE 11 pin 1 which sits at 5.65V.

"UE15 pin 4
UE14 pin 8
UE11 pin 6
UE11 pin 8
UE13 pin 6
UE11 pin 1
UE11 pin 2
UE11 pin 3
UD4 pin 8
UD4 pin 6"

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Old 20th Jul 2023, 1:12 pm   #227
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Default Re: Commodore PET 4032/8050/3022

All other smaller chips 5V supply is good (at 5.33V consistently) with the exception of UE16 which its at 7.53V but that looks different on the schematics to me anyway.

Colin.
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Old 20th Jul 2023, 1:13 pm   #228
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Default Re: Commodore PET 4032/8050/3022

Quote:
I have waveforms on all the below with the exceptionn of UE 11 pin 1 which sits at 5.65V.
OK, can you have a look at the UD10 CS problem and I will take a look at UE11 and see under what circumstances pin 1 should be active.

Edit: It's OK for UE11 pin 1 to be static-high as that comes from the R/W line. With the NOP tester running the line is constantly in the 'read' condition.

I will look at UE16 now to see why it has such an odd supply voltage.

Edit (2): Help me out here, where even is UE16 (which sheet?)

Last edited by SiriusHardware; 20th Jul 2023 at 1:22 pm.
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Old 20th Jul 2023, 1:20 pm   #229
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Default Re: Commodore PET 4032/8050/3022

Continuity is OK but I cannot get a waveform from UE12 pin 13. This is a new chip and socket btw.

Colin.


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Quote:
I get readings on all ROM chips with the exception of UD10 - that just goes high and stays there.
UD10 is one of the three BASIC 4 ROMS so it should be getting enabled periodically by the NOP generator. Its chip select comes directly from UE12 pin 13 (SEL B). Check again for a mainly high, momentarily low chip select pulse coming out of UE12 pin 13 and if you still have that, check continuity between UE12 pin 13 and UD10 pin 20.
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Old 20th Jul 2023, 1:24 pm   #230
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Default Re: Commodore PET 4032/8050/3022

UE16 is on sheet 3 of 11 in the middle of the page (split into two).

Colin.
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Old 20th Jul 2023, 1:28 pm   #231
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Default Re: Commodore PET 4032/8050/3022

I've just realised one thing though, I have always wondered why the ICs have different second letters A, B, C, D, E, etc. Looking at the layout diagram I've realised that all of the 'A' devices are in the first upper row of chips going across, all the 'B' devices are in the next row down, all the 'C' devices are in the middle row, all the 'D' devices are in the next row down and all the 'E' devices are in the lowest row.

At the same time the numbers in the part reference number ascend as you go from left to right, so it's essentially a way of telling you roughly whereabouts on the PCB the chip is - I've never realised that before. '

Last edited by SiriusHardware; 20th Jul 2023 at 1:34 pm.
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Old 20th Jul 2023, 1:31 pm   #232
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Default Re: Commodore PET 4032/8050/3022

Quote:
UE16 is on sheet 3 of 11 in the middle of the page (split into two).
Ah, got it now thanks. That is basically 4 x 2n2222 transistors in a chip style package, so it's OK for the voltages there to be outside of the normal range.
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Old 20th Jul 2023, 1:33 pm   #233
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Default Re: Commodore PET 4032/8050/3022

Lift UE12, gently bend out pin 13 to the side so it sits outside the socket and put it back in and power on. Do you get a waveform on pin 13 then?
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Old 20th Jul 2023, 2:00 pm   #234
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Default Re: Commodore PET 4032/8050/3022

Nope.

I'm not getting anything from pins 9,10,11 and 13 now.

Colin.


Quote:
Originally Posted by SiriusHardware View Post
Lift UE12, gently bend out pin 13 to the side so it sits outside the socket and put it back in and power on. Do you get a waveform on pin 13 then?
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Old 20th Jul 2023, 2:03 pm   #235
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Default Re: Commodore PET 4032/8050/3022

Isn't that an exact re-run of the fault you replaced the original chip for?

Check pins 23, 22, 21, 20 of UE12 in that order. They should have squarewave waveforms on them, with the frequency halving as you go from 23 , to 22, to 21, to 20.
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Old 20th Jul 2023, 2:13 pm   #236
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Default Re: Commodore PET 4032/8050/3022

23, 22 and 20 are good, but I get nothing from 21.

I am now confused again (but not desperate).

Colin.
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Old 20th Jul 2023, 2:17 pm   #237
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Default Re: Commodore PET 4032/8050/3022

Check for a squarewave waveform on UD14 pin 5. If present, power off and check for continuity between UD14 pin 5 and UE12 pin 21.
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Old 20th Jul 2023, 2:30 pm   #238
ScottishColin
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Default Re: Commodore PET 4032/8050/3022

Nothing there, but I have continuity.

I believe pin 5 connects to pin 15 of UD14? If so there is nothing there. I believe that connects to pin 24 of the 6502 which does have a waveform and also has continuity to pin 15 of UD14.

I have replaced the chip in UD14 but get the same symptoms.

Even more confused now.

Colin.


Quote:
Originally Posted by SiriusHardware View Post
Check for a squarewave waveform on UD14 pin 5. If present, power off and check for continuity between UD14 pin 5 and UE12 pin 21.
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Old 20th Jul 2023, 2:45 pm   #239
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Default Re: Commodore PET 4032/8050/3022

If I understand you correctly you seem to be reporting an impossible combination of results:

-Waveform on CPU 24
-Continuity from CPU pin 24 to UD14 pin 15
-No waveform on UD14 pin 15

The last of those three statements is impossible if the first two are true. Want to have another look at it?

I am wondering if there is a bad connection to the UD14 socket pin 15 which comes and goes as it pleases. That would certainly account for the apparently intermittent nature of the problem. First we didn't have those output waveforms on 9-12 of UE12, then we did, and now we don't again.

What you are aiming to see is that squarewave waveform going all the way from the CPU pin 24 to UD14 pin 15, through the gate in UD14 and out on 5 pin of UD14 and onwards to pin 21 of UE12.
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Old 20th Jul 2023, 5:22 pm   #240
ScottishColin
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Default Re: Commodore PET 4032/8050/3022

It's the NOP tester, or more specifically the DIL socket I have it plugged into. I'll sort it first.

Colin.
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