Non-working Commodore PET 3016 - Page 37 - UK Vintage Radio Repair and Restoration Discussion Forum

ScottishColin · 1st Mar 2021, 1:03 pm

OK - I've gone through UD6-UD9 pins 9, 10 and 11 (DA0-DA2) and got some varying results.

UD6
If I use Pin 20 on UD9, I get waves of c. 2V on pin 9, 4V pin 10 and 4V pin11.

However, if I use Pin 20 on UD7, the waves on UD9 definitely go up to c. 4V, 5V and 5V

UD7 and 8 are giving me consistent waves of 3v, 5V (spiking to 6) and 5v (spiking to 6) on pins 9, 10 and 11 respectively.

UD9 will only give me square waves if I use pin 20 on another IC (eg UD8) - the same voltages as UD7 and 8. However, if I use pin 20 on UD9, I get waves but they are very much not square ones like the others.

Would a document with some graphs be more helpful?

Colin.

Quote:

Originally Posted by SiriusHardware

Resistances certainly look more uniform now although DA0 is a tad lower than the rest in both directiions.

What about DA0 and DA2 compared to the others on scope?
DA0 still half the size of the others?
DA2 still flatlined?

ScottishColin · 1st Mar 2021, 1:20 pm

Here's a document showing the difference in height of pins 9/10/11 UD9 against pin 20 UD9 or Pin 20 UD7.

https://drive.google.com/file/d/14l4...ew?usp=sharing

Colin.

ScottishColin · 1st Mar 2021, 1:55 pm

And as a final update this morning, I cannot get any waves from UD6 if I use pin 20 on UD6, only pin 20 from other PROMs.

Colin.

Mark1960 · 1st Mar 2021, 5:03 pm

DA0 is better when UD7 is enabled, but still driving to a lower voltage than the other data lines.

I don’t see the output on DA0 when UD8 or UD6 are enabled, but still suspect there is something loading the DA0 output of the proms and stopping them from driving as high as they should.

For the spikes on the data lines, I think this is just short time pulses with a 4MHz sample rate on 20us per division. You might want to check how they look at 10us or 5us per division, just to help your understanding of what you see on the scope, but I don’t have any concerns about those.

I think its time to consider removing the data bus buffer, maybe only the one connected to DA0. Unless anyone else thinks there is something else that could be stopping the proms driving DA0 to the same level as the other data lines.

dave cox · 1st Mar 2021, 5:10 pm

I think you proved earlier that the CPU was running through the whole address range (activity on A0-A15) so the PROM UD6 *should* be selected (pin 20 low) at some point. I would be following the pcb trace/continuity from UD6/20 back to whatever drives it - it will some kind of address decoder, but i can't find a handy schematic to go further !

dc

Mark1960 · 1st Mar 2021, 5:24 pm

Sirius shows the address decoding in #683.

I think Colin was seeing the chip enable at UD6 but no data with chip enable low, but maybe Colin could confirm.

ScottishColin · 1st Mar 2021, 5:52 pm

All the PIn 20s seem to be driven from UD2 pins 14,15,16,17 (Sheet 1 of the schematics).

Should I see continuity from those pins to pins 20 on UD6/7/8/9 when the power is off - or do they only get continuity when something actually happens in UD2?

Colin.

Quote:

Originally Posted by dave cox

I think you proved earlier that the CPU was running through the whole address range (activity on A0-A15) so the PROM UD6 *should* be selected (pin 20 low) at some point. I would be following the pcb trace/continuity from UD6/20 back to whatever drives it - it will some kind of address decoder, but i can't find a handy schematic to go further !

dc

ScottishColin · 1st Mar 2021, 5:58 pm

Here's what I see on Pin 11 (green) against either UD7 pin 20 (good) or UD6 pin 20 (bad).

https://drive.google.com/file/d/16nK...ew?usp=sharing

Colin.

Quote:

Originally Posted by Mark1960

Sirius shows the address decoding in #683.

I think Colin was seeing the chip enable at UD6 but no data with chip enable low, but maybe Colin could confirm.

ScottishColin · 1st Mar 2021, 6:29 pm

OK - I went back to UD2 pin 14 to see if that would trigger any data on the scope to UD6 Pin 11 - nothing, but it does with pin 15 (Sel D), so to me that points to a UD2 problem?

Colin.

ScottishColin · 1st Mar 2021, 6:50 pm

OK - just checked with power off - good continuity from pins 14, 15, 16 & 17 to UD6/20, UD7/20, UD8/20 & UD9/20 respectively.

Colin.

Quote:

Originally Posted by ScottishColin

All the PIn 20s seem to be driven from UD2 pins 14,15,16,17 (Sheet 1 of the schematics).

Should I see continuity from those pins to pins 20 on UD6/7/8/9 when the power is off - or do they only get continuity when something actually happens in UD2?

Colin.

Quote:

Originally Posted by dave cox

I think you proved earlier that the CPU was running through the whole address range (activity on A0-A15) so the PROM UD6 *should* be selected (pin 20 low) at some point. I would be following the pcb trace/continuity from UD6/20 back to whatever drives it - it will some kind of address decoder, but i can't find a handy schematic to go further !

dc

Mark1960 · 1st Mar 2021, 7:13 pm

Quote:

Originally Posted by ScottishColin

OK - I went back to UD2 pin 14 to see if that would trigger any data on the scope to UD6 Pin 11 - nothing, but it does with pin 15 (Sel D), so to me that points to a UD2 problem?

No I think UD2 is ok, you see the chip selects on UD6, 7, 8 and 9 change from high to low, but you don’t see any output on pin 11, DA2 from UD6 when UD6 chip select is low. I guess its possible that data in the first section of UD6 all has DA2 at 0, but it seems unlikely.

SiriusHardware · 1st Mar 2021, 7:19 pm

Doesn't seem to be anything wrong with UD2, which is producing the UD6 _CS1 (pin 20) pulse that you are showing on your yellow upper trace.

With power on, can you check the voltage on UD6 CS3 (pin 21)? (should be +5V).

When you are looking at UD6 pin 11 (D2) you are also looking at UD7 pin 7, UD8 pin 11, and UD9 pin 11 because all of those pins are connected together.

The fact that you have no activity on the D2 data line when UD6 _CS1 is low is surprising. As I recall, you just about got your Arduino Mega PROM reader working. If it's still lying around, try reading UD6 to see if it is still OK.

ScottishColin · 1st Mar 2021, 7:43 pm

4.94V - same as UD7/8/9 pin 21.

I'll check the PROM.

Colin.

Quote:

Originally Posted by ScottishColin

All the PIn 20s seem to be driven from UD2 pins 14,15,16,17 (Sheet 1 of the schematics).

Should I see continuity from those pins to pins 20 on UD6/7/8/9 when the power is off - or do they only get continuity when something actually happens in UD2?

Colin.

Quote:

Originally Posted by dave cox

I think you proved earlier that the CPU was running through the whole address range (activity on A0-A15) so the PROM UD6 *should* be selected (pin 20 low) at some point. I would be following the pcb trace/continuity from UD6/20 back to whatever drives it - it will some kind of address decoder, but i can't find a handy schematic to go further !

dc

Quote:

Originally Posted by SiriusHardware

Doesn't seem to be anything wrong with UD2, which is producing the UD6 _CS1 (pin 20) pulse that you are showing on your yellow upper trace.

With power on, can you check the voltage on UD6 CS3 (pin 21)? (should be +5V).

When you are looking at UD6 pin 11 (D2) you are also looking at UD7 pin 7, UD8 pin 11, and UD9 pin 11 because all of those pins are connected together.

The fact that you have no activity on the D2 data line when UD6 _CS1 is low is surprising. As I recall, you just about got your Arduino Mega PROM reader working. If it's still lying around, try reading UD6 to see if it is still OK.

ScottishColin · 1st Mar 2021, 8:18 pm

Good shout. It's blank - all 00s. Checked several times.

I checked UD7 with the same Arduino sketch and wiring and that reads ok.

Seems to me that I might need a new UD6....is this a fat-fingered possibility with the number of times I have been poking at it with a probe?

And can you point me at the right .bin so I can get a new UD6 from the same person as before?

Thanks.

Colin.

Quote:

Originally Posted by SiriusHardware

Doesn't seem to be anything wrong with UD2, which is producing the UD6 _CS1 (pin 20) pulse that you are showing on your yellow upper trace.

With power on, can you check the voltage on UD6 CS3 (pin 21)? (should be +5V).

When you are looking at UD6 pin 11 (D2) you are also looking at UD7 pin 7, UD8 pin 11, and UD9 pin 11 because all of those pins are connected together.

The fact that you have no activity on the D2 data line when UD6 _CS1 is low is surprising. As I recall, you just about got your Arduino Mega PROM reader working. If it's still lying around, try reading UD6 to see if it is still OK.

SiriusHardware · 1st Mar 2021, 8:49 pm

If it is duff, that's a shame - it was definitely OK when I had it (correct checksum, etc) but they are notoriously fragile. That's the one where the pin had broken off on the corner, isn't it, so maybe it's better in the long run to replace it anyway.

The file you would be looking for for UD6 is the one named thusly:-

basic-2-c000.901465-01.bin2009-08-18

under 'Files' on this page:-

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

UD7 which you've already replaced should have been programmed with the file named:-

basic-2-d000.901465-02.bin2009-08-18

If you are wondering how I know which code goes where, look closely at the circuit diagram of the PROMs, which shows the address range occupied by each PROM. UD6 = C000 onwards, UD7 = D000 onwards. Those two hexadecimal addresses are included as part of the file names above.

julie_m · 1st Mar 2021, 9:42 pm

The schematics for this PET model can be found here.

If you can't find the exact PROM at a reasonable price, it should be easy enough to bodge in the more readily available 2764. This even has enough room to do double duty as both UD6 and UD7.

ScottishColin · 1st Mar 2021, 9:51 pm

Thanks - I've found someone who supply and burn for a tenner so I'm happy with that. I'd love to know what I did.

I plan to get some new 24 pin sockets and put the PROMs into sockets so that if I need to remove them, I will remove the socket with the PROM in it, not just the PROM.

Hopefully that might save the legs a little if nothing else.

Colin.

Quote:

Originally Posted by julie_m

The schematics for this PET model can be found here.

If you can't find the exact PROM at a reasonable price, it should be easy enough to bodge in the more readily available 2764. This even has enough room to do double duty as both UD6 and UD7.

ajgriff · 1st Mar 2021, 10:09 pm

Quote:

Originally Posted by ScottishColin

I'd love to know what I did.

You probably didn't do anything. One thing I have learnt about early PETS is that chips can and do give up the ghost without the slightest provocation!

Alan

Mark1960 · 2nd Mar 2021, 2:53 am

Which of the proms was already replaced?

Does it show a better high voltage level than the others on DA0 ?

I think you still need to try and identify why DA0 is not showing a good high level. If it turns out to be the buffer its possible this could have caused the failure of UD6.

SiriusHardware · 2nd Mar 2021, 11:54 am

UD7 is the one which was recently replaced. When I had them briefly that was the only one of the four which was dud. I didn't get the character PROM UF10, but Colin read that with an Arduino shortly afterwards and it looked OK.

Shall we ask Colin to replace the data bus buffers if he is going to be waiting for a replacement UD6 anyway?

1st Mar 2021, 1:20 pm	#722
ScottishColin Octode Join Date: May 2012 Location: Perth, Scotland Posts: 1,802	Re: Non-working Commodore PET 3016 Here's a document showing the difference in height of pins 9/10/11 UD9 against pin 20 UD9 or Pin 20 UD7. https://drive.google.com/file/d/14l4...ew?usp=sharing Colin.

1st Mar 2021, 1:55 pm	#723
ScottishColin Octode Join Date: May 2012 Location: Perth, Scotland Posts: 1,802	Re: Non-working Commodore PET 3016 And as a final update this morning, I cannot get any waves from UD6 if I use pin 20 on UD6, only pin 20 from other PROMs. Colin.

1st Mar 2021, 5:03 pm	#724
Mark1960 Octode Join Date: Mar 2020 Location: Kitchener, Ontario, Canada Posts: 1,294	Re: Non-working Commodore PET 3016 DA0 is better when UD7 is enabled, but still driving to a lower voltage than the other data lines. I don’t see the output on DA0 when UD8 or UD6 are enabled, but still suspect there is something loading the DA0 output of the proms and stopping them from driving as high as they should. For the spikes on the data lines, I think this is just short time pulses with a 4MHz sample rate on 20us per division. You might want to check how they look at 10us or 5us per division, just to help your understanding of what you see on the scope, but I don’t have any concerns about those. I think its time to consider removing the data bus buffer, maybe only the one connected to DA0. Unless anyone else thinks there is something else that could be stopping the proms driving DA0 to the same level as the other data lines.

1st Mar 2021, 5:10 pm	#725
dave cox Nonode Join Date: Jan 2009 Location: Bristol, UK. Posts: 2,061	Re: Non-working Commodore PET 3016 I think you proved earlier that the CPU was running through the whole address range (activity on A0-A15) so the PROM UD6 should be selected (pin 20 low) at some point. I would be following the pcb trace/continuity from UD6/20 back to whatever drives it - it will some kind of address decoder, but i can't find a handy schematic to go further ! dc

1st Mar 2021, 5:24 pm	#726
Mark1960 Octode Join Date: Mar 2020 Location: Kitchener, Ontario, Canada Posts: 1,294	Re: Non-working Commodore PET 3016 Sirius shows the address decoding in #683. I think Colin was seeing the chip enable at UD6 but no data with chip enable low, but maybe Colin could confirm.

1st Mar 2021, 6:29 pm	#729
ScottishColin Octode Join Date: May 2012 Location: Perth, Scotland Posts: 1,802	Re: Non-working Commodore PET 3016 OK - I went back to UD2 pin 14 to see if that would trigger any data on the scope to UD6 Pin 11 - nothing, but it does with pin 15 (Sel D), so to me that points to a UD2 problem? Colin.

1st Mar 2021, 7:19 pm	#732
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,546	Re: Non-working Commodore PET 3016 Doesn't seem to be anything wrong with UD2, which is producing the UD6 _CS1 (pin 20) pulse that you are showing on your yellow upper trace. With power on, can you check the voltage on UD6 CS3 (pin 21)? (should be +5V). When you are looking at UD6 pin 11 (D2) you are also looking at UD7 pin 7, UD8 pin 11, and UD9 pin 11 because all of those pins are connected together. The fact that you have no activity on the D2 data line when UD6 _CS1 is low is surprising. As I recall, you just about got your Arduino Mega PROM reader working. If it's still lying around, try reading UD6 to see if it is still OK.

1st Mar 2021, 8:49 pm	#735
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,546	Re: Non-working Commodore PET 3016 If it is duff, that's a shame - it was definitely OK when I had it (correct checksum, etc) but they are notoriously fragile. That's the one where the pin had broken off on the corner, isn't it, so maybe it's better in the long run to replace it anyway. The file you would be looking for for UD6 is the one named thusly:- basic-2-c000.901465-01.bin2009-08-18 under 'Files' on this page:- http://www.zimmers.net/anonftp/pub/c...pet/index.html UD7 which you've already replaced should have been programmed with the file named:- basic-2-d000.901465-02.bin2009-08-18 If you are wondering how I know which code goes where, look closely at the circuit diagram of the PROMs, which shows the address range occupied by each PROM. UD6 = C000 onwards, UD7 = D000 onwards. Those two hexadecimal addresses are included as part of the file names above. Attached Thumbnails Last edited by SiriusHardware; 1st Mar 2021 at 8:58 pm.

1st Mar 2021, 9:42 pm	#736
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: Non-working Commodore PET 3016 The schematics for this PET model can be found here. If you can't find the exact PROM at a reasonable price, it should be easy enough to bodge in the more readily available 2764. This even has enough room to do double duty as both UD6 and UD7. __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

2nd Mar 2021, 2:53 am	#739
Mark1960 Octode Join Date: Mar 2020 Location: Kitchener, Ontario, Canada Posts: 1,294	Re: Non-working Commodore PET 3016 Which of the proms was already replaced? Does it show a better high voltage level than the others on DA0 ? I think you still need to try and identify why DA0 is not showing a good high level. If it turns out to be the buffer its possible this could have caused the failure of UD6.

2nd Mar 2021, 11:54 am	#740
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,546	Re: Non-working Commodore PET 3016 UD7 is the one which was recently replaced. When I had them briefly that was the only one of the four which was dud. I didn't get the character PROM UF10, but Colin read that with an Arduino shortly afterwards and it looked OK. Shall we ask Colin to replace the data bus buffers if he is going to be waiting for a replacement UD6 anyway?