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Commodore PET CBM 4016 ASSY 8032080 RIFA burn and more
- Thread starter DrAlis
- Start date
daver2
10k Member
Yes, pin 9 looks good.
Either set the oscilloscope into a 'one shot' mode, or else 'sweep' the timebase.
I will give you some more pins to check shortly.
Dave
Either set the oscilloscope into a 'one shot' mode, or else 'sweep' the timebase.
I will give you some more pins to check shortly.
Dave
daver2
10k Member
OK, I am going to start from the 'outside in'.
I need to know whether each pin is HIGH, LOW or PULSING again. Remember to adjust your oscilloscope timebase to make sure you are not missing things.
UC3 pins 7, 9, 10, and 11.
UB1 pins 2 and 3.
UA2 pin 13.
UC2 pins 8, 9, and 10.
UD4 pins 1, 2, 12, and 13.
Based upon what we see, we will try and home in on the problem.
Dave
I need to know whether each pin is HIGH, LOW or PULSING again. Remember to adjust your oscilloscope timebase to make sure you are not missing things.
UC3 pins 7, 9, 10, and 11.
UB1 pins 2 and 3.
UA2 pin 13.
UC2 pins 8, 9, and 10.
UD4 pins 1, 2, 12, and 13.
Based upon what we see, we will try and home in on the problem.
Dave
daver2
10k Member
There are a few errors there...
UB1 pin 3 should be a 1 MHz clock. Can you recheck this pin again please?
There should also be some activity on the pins we looked at on UC3.
Can you check UC3 pins 1, 2, 3, 4, 5 and 6. Let's see what signals are going into UC3.
Dave
UB1 pin 3 should be a 1 MHz clock. Can you recheck this pin again please?
There should also be some activity on the pins we looked at on UC3.
Can you check UC3 pins 1, 2, 3, 4, 5 and 6. Let's see what signals are going into UC3.
Dave
I correct: UB1: pin 3: pulse (oszi claims 2 mhz, photo below)
I add: UC3: pins 1 to 8: low pulse high pulse (something sometimes happening here with around 1hz as well) pulse pulse high low
i feel it changes while it runs - seems pettester is running?
I add: UC3: pins 1 to 8: low pulse high pulse (something sometimes happening here with around 1hz as well) pulse pulse high low
i feel it changes while it runs - seems pettester is running?
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daver2
10k Member
I am a little concerned about continuing until we can ensure that we get correct measurements first time.
Your oscilloscope states 2 MHz fir UB1 pin 3. However, if the oscilloscope has a tinebase setting of 250 ns/div, then the period of the clock is 4 divisions = 1,000 ns = 1 us = 1 MHz.
It could be that the oscilloscope trigger level us too low, and it is picking up some 'bounce'. This may account for the indication of 2 MHz? But we need to get this resolved. It should be 1 MHz, not 2 MHz.
Likewise UC3 pin 3. You have identified this as HIGH, but it should also be pulsing at 1 MHz.
If we can't write to (or read from video RAM) this should not give us a blank screen - but a random one. I therefore suspect we are looking at two concurrent faults.
Is your PET configured for 40 or 80 columns? 40 Columns (J7 installed) would account for UC3 pin 1 being LOW, otherwise (80 columns with J8 installed) would indicate a problem with this pin (or pin measurement).
Dave
Your oscilloscope states 2 MHz fir UB1 pin 3. However, if the oscilloscope has a tinebase setting of 250 ns/div, then the period of the clock is 4 divisions = 1,000 ns = 1 us = 1 MHz.
It could be that the oscilloscope trigger level us too low, and it is picking up some 'bounce'. This may account for the indication of 2 MHz? But we need to get this resolved. It should be 1 MHz, not 2 MHz.
Likewise UC3 pin 3. You have identified this as HIGH, but it should also be pulsing at 1 MHz.
If we can't write to (or read from video RAM) this should not give us a blank screen - but a random one. I therefore suspect we are looking at two concurrent faults.
Is your PET configured for 40 or 80 columns? 40 Columns (J7 installed) would account for UC3 pin 1 being LOW, otherwise (80 columns with J8 installed) would indicate a problem with this pin (or pin measurement).
Dave
Dear Dave,
ok UB1 Pin 3 is 1 MHz as you correctly derived from the waveform. It turns out the trigger setting does matter for the frequency shown. I assumed the frequency shown is somehow calculated from the waveform by some smart algorithm. I guess it just counts trigger passes. Pffff... Dave, that is what happens if you work with people that picked this hobby without any formal or informal education in electronics.
Somebody want to recommend a good read/view on osci use?
However, I stand firm on UC3 pin 3. I can not find any activity there on any timescale. High high high. (Unless I did something wrong.)
It is a 40 column.
I fully understand your concern around my measurement performance. I am just a really fresh clueless apprentice (in this domain) figuring stuff out as we go along. We are both doing this for fun, I hope. Also if easy: Could you please point me / post the Zimmer schematic that you are using currently. You gave me the link before, but I still find the material hard to impossible to navigate. Thanks for your patience!
ok UB1 Pin 3 is 1 MHz as you correctly derived from the waveform. It turns out the trigger setting does matter for the frequency shown. I assumed the frequency shown is somehow calculated from the waveform by some smart algorithm. I guess it just counts trigger passes. Pffff... Dave, that is what happens if you work with people that picked this hobby without any formal or informal education in electronics.
Somebody want to recommend a good read/view on osci use?However, I stand firm on UC3 pin 3. I can not find any activity there on any timescale. High high high. (Unless I did something wrong.)
It is a 40 column.
I fully understand your concern around my measurement performance. I am just a really fresh clueless apprentice (in this domain) figuring stuff out as we go along. We are both doing this for fun, I hope. Also if easy: Could you please point me / post the Zimmer schematic that you are using currently. You gave me the link before, but I still find the material hard to impossible to navigate. Thanks for your patience!
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daver2
10k Member
Oscilloscopes are not (generally) smart... You should (when measuring the frequency) make sure the trigger point is midway on the trace to ensure that the oscilloscope is not reading undershoot or overshoot (bounce) as I suspect it was. This comes with practice and knowledge...
The Tektronix website has some good reference material. See https://www.tek.com/en/documents/primer/setting-and-using-oscilloscope and https://www.tek.com/en/documents/primer/oscilloscope-basics for examples. There is also a Learning Centre https://www.tek.com/en/support/learning-center.
There is other material around - but I would go for the major manufacturers of oscilloscopes to ensure you are not getting suckered into bad practices.
The website you want is: https://www.zimmers.net/anonftp/pub/cbm/schematics/computers/pet/univ/index.html.
You have identified that your board assembly is 8032080. This makes it either an 8032, a Univ or a Univ2. Check each of the three Zimmers directories until you find the one with the assembly/parts list matching your board.
The parts list (if you look at 8032080-02) identifies a PCB of 8032079 and a logic (schematic) diagram of 8032081. These are the diagrams you want...
What we have just been looking at was: https://www.zimmers.net/anonftp/pub/cbm/schematics/computers/pet/univ/8032081-08.gif.
Glad your machine is a 40-column machine. I was just querying UC3 pin 1 that was LOW in a previous post.
If the machine is 40 column (40C) UC3 pin 1 will be connected to 0V via J7 - so this is correct. In 80 column mode (80C) UC3 pin 1 should be connected to BA0 (via J8) and it should have had a signal on it...
If UC3 pin 3 truly doesn't have a clock of 1 MHz on it, we need to work our way back to find out where it has gone!
It says it comes from sheet -06.
It does, and it doesn't! If you chase this signal back to sheet 6, it comes (ultimately) from sheet -01 - so that is where we need to go to.
Check the 6502 CPU pin 39. The 1 MHz clock should be present here.
This signal is then buffered by UD15. The clock signal goes 'in' on pin 1 and comes 'out' from pin 2. Check both these pins for our 1 MHz clock.
If it is present on UD15 pin 2, there must either be a break in the PCB track or something is dragging the signal HIGH or LOW.
You can 'chase' the signal from sheet -01 to sheets -02, -03 and -06. Look for the signal on these sheets (IC pins) and see if the 1 MHz clock is present or not.
Note that resistor R13 must be present and working. The resistor pulls up the signal to +5V, and UD15 pulls it down to 0V (when required).
>>> We are both doing this for fun, I hope.
Yep. Well, I am trying to pass on my knowledge to others as we try to find the fault. Keep asking the questions - I am happy to answer them...
Dave
The Tektronix website has some good reference material. See https://www.tek.com/en/documents/primer/setting-and-using-oscilloscope and https://www.tek.com/en/documents/primer/oscilloscope-basics for examples. There is also a Learning Centre https://www.tek.com/en/support/learning-center.
There is other material around - but I would go for the major manufacturers of oscilloscopes to ensure you are not getting suckered into bad practices.
The website you want is: https://www.zimmers.net/anonftp/pub/cbm/schematics/computers/pet/univ/index.html.
You have identified that your board assembly is 8032080. This makes it either an 8032, a Univ or a Univ2. Check each of the three Zimmers directories until you find the one with the assembly/parts list matching your board.
The parts list (if you look at 8032080-02) identifies a PCB of 8032079 and a logic (schematic) diagram of 8032081. These are the diagrams you want...
What we have just been looking at was: https://www.zimmers.net/anonftp/pub/cbm/schematics/computers/pet/univ/8032081-08.gif.
Glad your machine is a 40-column machine. I was just querying UC3 pin 1 that was LOW in a previous post.
If the machine is 40 column (40C) UC3 pin 1 will be connected to 0V via J7 - so this is correct. In 80 column mode (80C) UC3 pin 1 should be connected to BA0 (via J8) and it should have had a signal on it...
If UC3 pin 3 truly doesn't have a clock of 1 MHz on it, we need to work our way back to find out where it has gone!
It says it comes from sheet -06.
It does, and it doesn't! If you chase this signal back to sheet 6, it comes (ultimately) from sheet -01 - so that is where we need to go to.
Check the 6502 CPU pin 39. The 1 MHz clock should be present here.
This signal is then buffered by UD15. The clock signal goes 'in' on pin 1 and comes 'out' from pin 2. Check both these pins for our 1 MHz clock.
If it is present on UD15 pin 2, there must either be a break in the PCB track or something is dragging the signal HIGH or LOW.
You can 'chase' the signal from sheet -01 to sheets -02, -03 and -06. Look for the signal on these sheets (IC pins) and see if the 1 MHz clock is present or not.
Note that resistor R13 must be present and working. The resistor pulls up the signal to +5V, and UD15 pulls it down to 0V (when required).
>>> We are both doing this for fun, I hope.
Yep. Well, I am trying to pass on my knowledge to others as we try to find the fault. Keep asking the questions - I am happy to answer them...
Dave
daver2
10k Member
>>> i can bridge those two...
Please don't do that. This signal goes to multiple places.
Dave
Please don't do that. This signal goes to multiple places.
Dave
daver2
10k Member
EDIT: Don't necessarily trust the Commodore schematics (especially the scrawled pin numbers). Download the 6520 and 6522 datasheets and check the pin numbers. For both devices, the clock pin is 25 (as I detail below). Hence why looking at pin 23 you don't see 1 MHz - it is not the correct pin!
Check the following pins for our 1 MHz signal...
UD4 pin 11(74LS10).
UB16 pin 25 (6520 PIA).
UB2 pin 25 (6520 PIA).
UB15 pin 25 (6522 VIA).
See which pins have the signal and which do not.
With the PET power OFF, you can also use a multimeter (set to read a low resistance) for conductance between UD15 pin 2 and the other points mentioned above (don't forget to include UC3 pin 3 as well).
It is possible there is a track break or a via (from one side of the PCB to the other side) is open circuit.
You should be able to work out where by following the PCB track from UD15 pin 2 to all of the other locations using your oscilloscope or multimeter. As soon as the signal dissapears (or the track becomes open circuit) that is where we need to look at in detail.
Is this clear?
Dave
Check the following pins for our 1 MHz signal...
UD4 pin 11(74LS10).
UB16 pin 25 (6520 PIA).
UB2 pin 25 (6520 PIA).
UB15 pin 25 (6522 VIA).
See which pins have the signal and which do not.
With the PET power OFF, you can also use a multimeter (set to read a low resistance) for conductance between UD15 pin 2 and the other points mentioned above (don't forget to include UC3 pin 3 as well).
It is possible there is a track break or a via (from one side of the PCB to the other side) is open circuit.
You should be able to work out where by following the PCB track from UD15 pin 2 to all of the other locations using your oscilloscope or multimeter. As soon as the signal dissapears (or the track becomes open circuit) that is where we need to look at in detail.
Is this clear?
Dave
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daver2
10k Member
It is UB <blank> 2 on the Commodore schematic, so (yes) it is probably UB12! Another error on the schematics...
So, follow the pin and PCB track back from UC3 pin 3 looking for signs of PCB damage.
Unless we are chasing another Commodore schematic error...
The Univ2 has UC3 pin 3 pulled high and an additional gate before UC3. Your PCB is definitely marked 8032080 isn't it?
Dave
So, follow the pin and PCB track back from UC3 pin 3 looking for signs of PCB damage.
Unless we are chasing another Commodore schematic error...
The Univ2 has UC3 pin 3 pulled high and an additional gate before UC3. Your PCB is definitely marked 8032080 isn't it?
Dave
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daver2
10k Member
That pin is connected directly to +5V!
Are you doubly-sure this board is a 8032080?
It is a good thing we did NOT just bridge these two points!
Dave
Are you doubly-sure this board is a 8032080?
It is a good thing we did NOT just bridge these two points!
Dave
I have no idea that is why I posted the picture in the beginning. Also in the last picture you can see the numbers 8032080 on the right. Please tell me what this monster is. but if assy 8032080 is not a 8032080 then the documentation is an issue...
Good news if you can not figure out what this is, what chances do I have. Null...
that is why I posted the picture in the beginning. Also in the last picture you can see the numbers 8032080 on the right. Please tell me what this monster is. but if assy 8032080 is not a 8032080 then the documentation is an issue...Good news if you can not figure out what this is, what chances do I have. Null...
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daver2
10k Member
A univ board (universal) is an 8032080.
A univ2 (universal 2) is an 8032090.
Very close together, but the logic is different around UC3.
It is possible that the wire on UC3 may give us a clue if I lookup the ECOs (Engineering Change Orders) for the two boards. This will be tomorrow now.
In the meantime, could you see where UC3 pin 2 is connected to please?
You may have a very strange board. It could be marked as a 80 but is really a 90
?
Dave
A univ2 (universal 2) is an 8032090.
Very close together, but the logic is different around UC3.
It is possible that the wire on UC3 may give us a clue if I lookup the ECOs (Engineering Change Orders) for the two boards. This will be tomorrow now.
In the meantime, could you see where UC3 pin 2 is connected to please?
You may have a very strange board. It could be marked as a 80 but is really a 90
?Dave