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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 10th Mar 2021, 5:31 pm   #861
Mark1960
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Default Re: Non-working Commodore PET 3016

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Originally Posted by ScottishColin View Post
Nothing on either UF7/10 or UF8/10.
Is “Nothing” always high or always low?
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Old 10th Mar 2021, 5:39 pm   #862
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Default Re: Non-working Commodore PET 3016

Steady high state.

Colin.
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Old 10th Mar 2021, 5:42 pm   #863
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Default Re: Non-working Commodore PET 3016

I keep looking at the wrong schematic. Can someone please confirm the correct one is named 320349.pdf and runs to nine pages? If so I'll post a copy unless that's already been done earlier in the thread. Thanks.

Alan
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Old 10th Mar 2021, 5:46 pm   #864
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Default Re: Non-working Commodore PET 3016

This is a link to them online.

http://www.zimmers.net/anonftp/pub/c...ers/pet/2001N/

Of the pages ending in -1.gif to -9.gif, the one we are looking at at the moment is the display RAM, sheet 8.

http://www.zimmers.net/anonftp/pub/c...N/320349-8.gif
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Old 10th Mar 2021, 5:52 pm   #865
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Default Re: Non-working Commodore PET 3016

Colin: Do you see activity on the SD0 to SD7 pins of UF9? (Pins 3,18,4,17,7,14,8,13).... or are those lines all in steady states?
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Old 10th Mar 2021, 5:55 pm   #866
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Default Re: Non-working Commodore PET 3016

Steady high on all those pins on UF9.

Colin.
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Old 10th Mar 2021, 5:57 pm   #867
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Default Re: Non-working Commodore PET 3016

Thanks Sirius. For the benefit of anybody else who likes to see the whole picture I've attached the PDF for the entire system board.

Alan
Attached Files
File Type: pdf 320349.pdf (1.72 MB, 16 views)
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Old 10th Mar 2021, 6:00 pm   #868
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Default Re: Non-working Commodore PET 3016

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Steady high on all those pins on UF9.
Steady high states on all those pins is consistent with you having the same character repeating over and over again, although it's not quite clear why 11111111 would translate to ';'.

Next up, look for activity on the A0 to A9 pins of UF8 (5,6,7,4,3,2,1,17,16,15). Do you see activity, or steady states, on those pins?
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Old 10th Mar 2021, 7:02 pm   #869
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Default Re: Non-working Commodore PET 3016

I'm getting square waves that are consistent on all of those pins. There seems to be activity (in that the waves 'shift' a little and have larger and smaller gaps between them over time, but they're all the same height and shape.

***EDIT - checked UF7 and it's the same as UF8 ***

Colin.
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Old 10th Mar 2021, 7:49 pm   #870
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Default Re: Non-working Commodore PET 3016

The way I think this is supposed to work is that the address lines SA0-SA9 continually count up from 0000000000 to 1111111111, and at each different address the Video_Latch signal pulses to latch the data coming out of UF7-UF8 into UF9. Problem is that instead of the random data you might expect from un-initialised RAM, you seem to have steady high states on the outputs of the RAM even though the address is continually changing.

Apart from the RAM itself, the only other place those steady highs can be coming from is the buffer pair UE7 UE8, but (if working) they should only place data on the SD0.. SD7 lines when their pin 19s are low.

The two pin 19s are connected to the RAM R/W pins (10) and you have already said that line is steady high, so the buffers should be disabled and the RAM ICs enabled in read mode.

Therefore, what you see on SD0-SD7 is either coming out of the RAMs, or the RAMs are not placing their contents on the SD0-SD7 lines.

Anyone have any thoughts on this?

Could you check to see if the RAMs both have +5V on their pins (18)?
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Old 10th Mar 2021, 8:02 pm   #871
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Default Re: Non-working Commodore PET 3016

Wow you look away for an evening and the world shifts - well done, a screen display...

You say you get square waves on the scope on the address lines can you check the shape of SD0-SD3 UF8 11-14 and the same for UF7 pins to see if they are nice clean 0-4V square waves - if not we could have a line driver issue again or a select suppressing / raising that short section into the latch.

It should be the same results as the data requested in post #865 - should have read more closely or have we not seen the answer to that yet?
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Old 10th Mar 2021, 8:03 pm   #872
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Default Re: Non-working Commodore PET 3016

You could check the video RAMs by swapping them over with a couple of the system RAM chips. Might change, or otherwise, the display output which could give some clues.

Alan
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Old 10th Mar 2021, 8:06 pm   #873
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Default Re: Non-working Commodore PET 3016

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Originally Posted by ajgriff View Post
You could check the video RAMs by swapping them over with a couple of the system RAM chips. Might change, or otherwise, the display output which could give some clues.

Alan
If they are socketed just swapping them over should change from a ; as

3B or 00111011

will be

B3 or 10110011
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Old 10th Mar 2021, 8:06 pm   #874
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Default Re: Non-working Commodore PET 3016

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check the shape of SD0-SD3 UF8 11-14 and the same for UF7 pins to see if they are nice clean 0-4V square waves
Those pins (four from UF7, four from UF8) go to the eight inputs on UF9 and Colin says he has steady high on all of those.

Doesn't mean that it is not also worth looking on UF7 pins 11-14 and UF8 pins 11-14 but it's hard to imagine where all 8 of those signals would go missing on the way to UF9.
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Old 10th Mar 2021, 8:07 pm   #875
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Default Re: Non-working Commodore PET 3016

I'm afraid none of the RAMS are socketed as far as I know.
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Old 10th Mar 2021, 8:24 pm   #876
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Default Re: Non-working Commodore PET 3016

5.30V confirmed on both pin 18s.

Colin.


Quote:
Originally Posted by SiriusHardware View Post
The way I think this is supposed to work is that the address lines SA0-SA9 continually count up from 0000000000 to 1111111111, and at each different address the Video_Latch signal pulses to latch the data coming out of UF7-UF8 into UF9. Problem is that instead of the random data you might expect from un-initialised RAM, you seem to have steady high states on the outputs of the RAM even though the address is continually changing.

Apart from the RAM itself, the only other place those steady highs can be coming from is the buffer pair UE7 UE8, but (if working) they should only place data on the SD0.. SD7 lines when their pin 19s are low.

The two pin 19s are connected to the RAM R/W pins (10) and you have already said that line is steady high, so the buffers should be disabled and the RAM ICs enabled in read mode.

Therefore, what you see on SD0-SD7 is either coming out of the RAMs, or the RAMs are not placing their contents on the SD0-SD7 lines.

Anyone have any thoughts on this?

Could you check to see if the RAMs both have +5V on their pins (18)?
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Old 10th Mar 2021, 8:28 pm   #877
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Default Re: Non-working Commodore PET 3016

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Originally Posted by SiriusHardware View Post
I'm afraid none of the RAMS are socketed as far as I know.
Sorry, forgot about that. Too much time spent staring at a 2001-8 motherboard.

Alan
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Old 10th Mar 2021, 8:28 pm   #878
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Default Re: Non-working Commodore PET 3016

Yep - all RAM chips are soldered on this motherboard.

Colin.


Quote:
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I'm afraid none of the RAMS are socketed as far as I know.
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Old 10th Mar 2021, 8:40 pm   #879
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Default Re: Non-working Commodore PET 3016

11-14 on UF7 and UF8 are steady high.

Colin.

Quote:
Originally Posted by SiriusHardware View Post
Quote:
check the shape of SD0-SD3 UF8 11-14 and the same for UF7 pins to see if they are nice clean 0-4V square waves
Those pins (four from UF7, four from UF8) go to the eight inputs on UF9 and Colin says he has steady high on all of those.

Doesn't mean that it is not also worth looking on UF7 pins 11-14 and UF8 pins 11-14 but it's hard to imagine where all 8 of those signals would go missing on the way to UF9.
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Old 10th Mar 2021, 8:44 pm   #880
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Default Re: Non-working Commodore PET 3016

Quote:
Yep - all RAM chips are soldered on this motherboard.
Which lands us with a bit of a headache, because the simple tests which Tim and AJ suggested are not easily possible.

So far when we have suspected an IC might be dud they have always been something quite run of the mill and with the exception of the CPU, relatively cheap and easy to replace. With something as exotic as the 6114 RAMs I really prefer not to take the approach of hacking them to pieces on the off chance that they may be faulty.

PET specialists among us - is it possible that the video RAM is being intentionally filled with FF during the early stages of initialisation?

Colin: You're obviously a lot more comfortable with removing and replacing ICs now, but how have you been doing that, by cutting the pins, removing the chip body and then removing the pins individually?
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