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Old 18th Mar 2021, 2:12 pm   #1141
ScottishColin
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Default Re: Non-working Commodore PET 3016

OK - device fitted. Main difference is that the screen is full of characters, and does not clear.

UI10/11 pin 1 - go high and stay there. Checked at 4.30V with a meter.

RAM chips - pin 4 has no reading (ie it stays at the same level with and without the scope connected. I checked the voltage at 0.40V on all RAM chips.

Pin 15 goes high and stays there - again checked with a meter at 4.30V constant.

Scope readings to follow.

Colin.



Quote:
Originally Posted by SiriusHardware View Post
Quote:
...and in a straightforward manner that would be ideal. Unfortunately I don't have sufficient knowledge to comment on the viability of this as an option
Me neither, at least not without using a diagnostic ROM, which remains an option.

The only other sure way to do it is to remove them all intact and use something else, like an Arduino, to independently test them.

Or remove them all intact, fit sockets and if possible fit combinations of them to try to find a combination of 8 out of 16 of them which will work as 8K, if that is a valid combination in these machines. Then cycle through the remaining ones to find out which ones stop the machine from working, much as you did with yours.

My suggestions before that:-

Fit the NOP tester in place of the CPU and check again to see if there is activity on UI10 / UI11 pin 1. If so, then it just shows that the CPU is currently getting into a loop or a mode where it is just not attempting to read from system RAM, and we can disregard the lack of activity there when the CPU is fitted.

Similarly, the RAS and CAS lines of the system RAM, pins 4 and 15 on each 4108 chip. Is there activity there during a NOP test?

Lastly, still while running the NOP test, scope the BD0 to BD7 lines again to see what they look like.

UI10 pins 11-12
UI10 pins 13-14
UI10 pins 15-16
UI10 pins 17-18
UI11 pins 11-12
UI11 pins 13-14
UI11 pins 15-16
UI11 pins 17-18
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Old 18th Mar 2021, 2:26 pm   #1142
ScottishColin
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Default Re: Non-working Commodore PET 3016

OK - scope readings attached - see last page as well.

I'm getting a flickering between the square waves and a roughly 1V reading. I've tried to attach a video so you can see what I can't capture with a screenshot.

https://drive.google.com/file/d/1LSZ...ew?usp=sharing

https://photos.app.goo.gl/JdbGZ89z5evNXo9z7

Colin.


Quote:
Originally Posted by ScottishColin View Post
OK - device fitted. Main difference is that the screen is full of characters, and does not clear.

UI10/11 pin 1 - go high and stay there. Checked at 4.30V with a meter.

RAM chips - pin 4 has no reading (ie it stays at the same level with and without the scope connected. I checked the voltage at 0.40V on all RAM chips.

Pin 15 goes high and stays there - again checked with a meter at 4.30V constant.

Scope readings to follow.

Colin.



Quote:
Originally Posted by SiriusHardware View Post
Quote:
...and in a straightforward manner that would be ideal. Unfortunately I don't have sufficient knowledge to comment on the viability of this as an option
Me neither, at least not without using a diagnostic ROM, which remains an option.

The only other sure way to do it is to remove them all intact and use something else, like an Arduino, to independently test them.

Or remove them all intact, fit sockets and if possible fit combinations of them to try to find a combination of 8 out of 16 of them which will work as 8K, if that is a valid combination in these machines. Then cycle through the remaining ones to find out which ones stop the machine from working, much as you did with yours.

My suggestions before that:-

Fit the NOP tester in place of the CPU and check again to see if there is activity on UI10 / UI11 pin 1. If so, then it just shows that the CPU is currently getting into a loop or a mode where it is just not attempting to read from system RAM, and we can disregard the lack of activity there when the CPU is fitted.

Similarly, the RAS and CAS lines of the system RAM, pins 4 and 15 on each 4108 chip. Is there activity there during a NOP test?

Lastly, still while running the NOP test, scope the BD0 to BD7 lines again to see what they look like.

UI10 pins 11-12
UI10 pins 13-14
UI10 pins 15-16
UI10 pins 17-18
UI11 pins 11-12
UI11 pins 13-14
UI11 pins 15-16
UI11 pins 17-18
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Old 18th Mar 2021, 2:28 pm   #1143
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Default Re: Non-working Commodore PET 3016

Quote:
Originally Posted by ScottishColin View Post
Tried this - no difference (ie blank screen which has power).
That's actually quite informative if the 2001-8 is anything to go by because it suggests that:

1. The PET might be getting past the character screen stage of the boot process without the PIAs in place.

2. At least one of the PIAs is probably faulty.

For what it's worth both 6520 PIAs were faulty in my PET. Failure of PIA2 resulted in the random character screen and PIA1 caused a problem with the internal datasette port.

I wouldn't do anything about the PIAs at the moment. Leave that until progress has been made with the RAM issues. Ultimately if one or both PIAs needs replacing there are reasonably priced alternatives to the original 6520s. Perhaps best to cross that bridge when we come to it.

Alan
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Old 18th Mar 2021, 3:07 pm   #1144
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Default Re: Non-working Commodore PET 3016

Quote:
OK - device fitted. Main difference is that the screen is full of characters, and does not clear.
When you say 'device fitted' I imagine you mean the NOP tester, and probably in its original form. If so that should be generating reads from every memory address from 0000 to FFFF and some of those should be from the system RAM, yet you appear to have no system RAM read activity through UI10 / UI11 because the read mode of those buffers is never being activated, that is, pin 1 of those buffers is never being taken low.

I expected you would get a screen full of random characters with the NOP device in because instead of executing the PROM code (which includes a routine to clear the screen) the CPU is just executing continual NOP instructions, so never clears the screen RAM.

I'll have to wait until this evening before taking a look at the scope traces - duty calls.
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Old 18th Mar 2021, 3:50 pm   #1145
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Default Re: Non-working Commodore PET 3016

In post #1142 you are listing pairs of pin numbers, but only one trace is active in each scope capture. Was it the first or second pin that was on the active trace?

With the NOP generator connected the 6502 is scanning through all 64 K addresses, but the ram is only active during the first 16 K of those, so it does look correct that there would be some flicking of the signal between active and inactive.
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Old 18th Mar 2021, 4:03 pm   #1146
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Default Re: Non-working Commodore PET 3016

Try to trace /RAS0 back to its source, look for activity on UG1-12 and UG1-13 with the scope.

Also check activity on UH1-3 and UH1-11.
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Old 18th Mar 2021, 4:14 pm   #1147
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Default Re: Non-working Commodore PET 3016

Tracing the /CAS signals back, check for activity on UH4-12.

Both /CAS and /RAS depend on UH4 so this might be a common fault for both problems.
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Old 18th Mar 2021, 4:30 pm   #1148
SiriusHardware
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Default Re: Non-working Commodore PET 3016

Quote:
In post #1142 you are listing pairs of pin numbers, but only one trace is active in each scope capture.
The second pin in each line in #1142 is directly connected to the first pin in each line, that is, they are electrically the same place, hence only one scope trace per pair of pins.

Quote:
it does look correct that there would be some flicking of the signal between active and inactive.
In principle yes, but remember that we do not seem to be getting a buffer read enable signal for UI10/UI11 on their pins 1s, therefore those buffers will not be passing the system RAM content through to BD0-BD7. If we do see activity on BD0-BD7 it may therefore be other devices on the BD0-BD7 lines which are creating the periodic activity - the flat-line / inactive periods may be the very periods when we should be seeing the output from the system RAM.

Last edited by SiriusHardware; 18th Mar 2021 at 4:49 pm.
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Old 18th Mar 2021, 4:58 pm   #1149
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Default Re: Non-working Commodore PET 3016

These readings are all with the NOP device in place.

UG1-12 - no movement on the scope.

UG1-13 - goes high (5V) and stays there)

UH1-3 - no movement on scope

UH1-11 - nice square waves attached.

Colin.


Quote:
Originally Posted by Mark1960 View Post
Try to trace /RAS0 back to its source, look for activity on UG1-12 and UG1-13 with the scope.

Also check activity on UH1-3 and UH1-11.
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Old 18th Mar 2021, 5:00 pm   #1150
ScottishColin
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Default Re: Non-working Commodore PET 3016

No activity (stays at zero) on UH-12.

NOP device still fitted.

Colin.


Quote:
Originally Posted by Mark1960 View Post
Tracing the /CAS signals back, check for activity on UH4-12.

Both /CAS and /RAS depend on UH4 so this might be a common fault for both problems.
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Old 18th Mar 2021, 5:04 pm   #1151
ScottishColin
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Default Re: Non-working Commodore PET 3016

All - I have not done anything with the idea in #1132, mainly because I don't know how....


Happy to try it but I'll need more detail I'm afraid.

Colin.
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Old 18th Mar 2021, 5:09 pm   #1152
SiriusHardware
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Default Re: Non-working Commodore PET 3016

I am still most concerned by the lack of any discernible activity on UI10 / UI11 pin 1, without which no data can pass from the system RAM to the buffered data bus.

In addition to Mark's suggestions to chase down the lack of activity on the RAS and CAS lines, could we also, with the NOP test now in place, revisit pins 9 and 11 of UG7 both at the same time so we can see the relationship between the two signals going to those points. I am particularly interested in knowing whether you ever see both of those signals high (~4-5V) at the same time.
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Old 18th Mar 2021, 5:31 pm   #1153
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Default Re: Non-working Commodore PET 3016

Quote:
Originally Posted by ScottishColin View Post
All - I have not done anything with the idea in #1132, mainly because I don't know how....


Happy to try it but I'll need more detail I'm afraid.

Colin.
Don’t bother with #1132 yet, we’ll get back to that when we find out why there is no activity on /RAS and /CAS.

Lack of outputs from UH4 is common to both, but might be a problem with its inputs.

UH5-1 should be 1MHz square wave.
UH5-2 should have some activity or held high.
UH5-3 should be 1MHz when UH5-2 is high.
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Old 18th Mar 2021, 5:40 pm   #1154
ScottishColin
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Default Re: Non-working Commodore PET 3016

Pin 9 goes high (5v). Pin 11 shifts slightly, but no waves (checked with meter at 0.4V).

Colin.

Quote:
Originally Posted by SiriusHardware View Post
I am still most concerned by the lack of any discernible activity on UI10 / UI11 pin 1, without which no data can pass from the system RAM to the buffered data bus.

In addition to Mark's suggestions to chase down the lack of activity on the RAS and CAS lines, could we also, with the NOP test now in place, revisit pins 9 and 11 of UG7 both at the same time so we can see the relationship between the two signals going to those points. I am particularly interested in knowing whether you ever see both of those signals high (~4-5V) at the same time.
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Old 18th Mar 2021, 5:40 pm   #1155
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Default Re: Non-working Commodore PET 3016

I think the BANK SEL signal should be active-high whenever an address in the system RAM address range is being read from or written to, this signal being decoded from the high address lines by one section of UB2, 7425 (input pins 9,10,12,13, output pin 8).

This BANK SEL output is in turn taken to one of the inputs of UG7, 74LS10, (inputs: 9,10,11, output: 8) which combines the BANK SEL signal with the buffered read / write signal 'B R/W' so that read pulses for the system RAM only occur during a read from the system RAM address block.

We aren't getting the read enable pulses for the system RAM out of UG7.

I note also that the BANK SEL signal feeds back to the main timing chain on sheet 6, and interestingly, it is also one of the initial inputs to the RAS/ CAS generation circuit.

BANK SEL and BØ2 (Buffered Φ2) go into UH5, 74LS00, (pins 2,1), output from UH5 pin 3 goes into pin 15 of UH4 which is at the heart of the RAS / CAS generator circuit - so a lack of BANK SEL signal could disable all of this as well as the system RAM read signal.

So the first question arising from all of that is: Is there any activity at all on the BANK SEL signal line, UB2 pin 8? - this is with the NOP test still running.

Edit: And Colin has just answered that question (pin 11 of UG7 is the same point as UB2 pin 8) - so we don't have a BANK SEL signal. This is a promising lead.

You know the jumpers on the mainboard, do they look as they have ever been tampered with or altered from their original settings? My understanding is that they are metal links which were either cut or left linked as required.

Last edited by SiriusHardware; 18th Mar 2021 at 5:47 pm.
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Old 18th Mar 2021, 5:43 pm   #1156
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Default Re: Non-working Commodore PET 3016

If BANK_SEL is always low that would explain both lack of /RAS and /CAS and also lack of signal at UI10-11 and UI11–11.

But that might be jumping ahead a little, lets see what Colin finds.

Edit: crossed post with Sirius.
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Old 18th Mar 2021, 5:45 pm   #1157
ScottishColin
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Default Re: Non-working Commodore PET 3016

UH5-1 confirmed 1Mhz waves (screenshot attached).

UH5-2 - no movement off baseline

UH5-3 goes high to a measured 4V.

Colin.


Quote:
Originally Posted by Mark1960 View Post
Quote:
Originally Posted by ScottishColin View Post
All - I have not done anything with the idea in #1132, mainly because I don't know how....


Happy to try it but I'll need more detail I'm afraid.

Colin.
Don’t bother with #1132 yet, we’ll get back to that when we find out why there is no activity on /RAS and /CAS.

Lack of outputs from UH4 is common to both, but might be a problem with its inputs.

UH5-1 should be 1MHz square wave.
UH5-2 should have some activity or held high.
UH5-3 should be 1MHz when UH5-2 is high.
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Old 18th Mar 2021, 5:47 pm   #1158
ScottishColin
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Default Re: Non-working Commodore PET 3016

UB2-8 screenshot attached.

Colin.


Quote:
Originally Posted by SiriusHardware View Post
I think the BANK SEL signal should be active-high whenever an address in the system RAM address range is being read from or written to, this signal being decoded from the high address lines by one section of UB2, 7425 (input pins 9,10,12,13, output pin 8).

This BANK SEL output is in turn taken to one of the inputs of UG7, 74LS10, (inputs: 9,10,11, output: 8) which combines the BANK SEL signal with the buffered read / write signal 'B R/W' so that read pulses for the system RAM only occur during a read from the system RAM address block.

We aren't getting the read enable pulses for the system RAM out of UG7.

I note also that the BANK SEL signal feeds back to the main timing chain on sheet 6, and interestingly, it is also one of the initial inputs to the RAS/ CAS generation circuit.

BANK SEL and BØ2 (Buffered Φ2) go into UH5, 74LS00, (pins 2,1), output from UH5 pin goes into pin 15 of UH4 which is at the heart of the RAS / CAS generator circuit - so a lack of BANK SEL signal could disable all of this as well as the system RAM read signal.

So the first question arising from all of that is: Is there any activity at all on the BANK SEL signal line, UB2 pin 8? - this is with the NOP test still running.

Edit: And Colin has just answered that question (pin 11 of UG7 is the same point as UB2 pin 8) - so we don't have a BANK SEL signal. This is a promising lead.

You know the jumpers on the mainboard, do they look as they have ever been tampered with or altered from their original settings? My understanding is that they are metal links which were either cut or left linked as required.
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Old 18th Mar 2021, 5:49 pm   #1159
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Default Re: Non-working Commodore PET 3016

For the jumpers on 16K pet, I think M, I and J should be fitted. L and H not fitted.
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Old 18th Mar 2021, 5:55 pm   #1160
SiriusHardware
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Default Re: Non-working Commodore PET 3016

Quote:
UB2-8 screenshot attached
!!?? You have a waveform on UB2-8 but you don't have the same waveform on UG7 pin 11? Please confirm that and if true, with power off, check continuity between

UB2 pin 8 and UG7 pin 11

and

UB2 pin 8 and UH5 pin 2
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