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Cbm 8032 capacitor

Reconnect J8 back to the PET logic board.

Set your multimeter to read DC Volts and connect the black lead of the multimeter to the negative (black wire) of the external capacitor.

With the red lead of the multimeter, check the following connector pins:

J8 pin 4 (key on pin 7). Approximately +9V.
J10 pin 4 (key on pin 3). Approximately +16V.
J11 pin 1 (key on pins 2 and 3). Approximately +9V.

If your multimeter can read both positive and negative voltages then skip the next step. If your multimeter can only read positive voltages, then swap the red and black leads over at the multimeter.

Read the voltage on J10 pin 1 (key on pin 3). Approximately -9V.

Report back the voltage readings for each measurement.

This should give us an idea what is going on.

Can I also ask you to look at bridge rectifiers CR2 and CR4 for signs of burning or damage.

Dave
 
Last edited:
And i don't know if this can change the results but i removed the expansion board for the tests so there is no processor on board
 
Excellent.

Did you accidentally measure J8 pin 1 instead of J10 pin 1?

-6V seems a bit low to me.

If so, can you remeasure at the correct point please.

Can you also measure the DC voltage on J8 pin 2 please. This was going to be my next voltage measurement anyhow.

Dave
 
Ibdon't know if this can help you but i give you all the voltages of j8
Pin
1 -6v
2 10v
3 10v
4 10v
5 -6v
6 10v
7 no pin
8 8.84 v
9 8.32 v
 
daver2 said:
Excellent.

Did you accidentally measure J8 pin 1 instead of J10 pin 1?

-6V seems a bit low to me.

If so, can you remeasure at the correct point please.

Can you also measure the DC voltage on J8 pin 2 please. This was going to be my next voltage measurement anyhow.

Dave
Click to expand...
Maybe the ram extension board is the problem ?
 
Lololobolosse said:
And i just spot that theres now 10v at the bic capacitor instead of 0.1v now
Click to expand...
I was just going to ask you to measure the voltage across the "big capacitor" and to verify that it is approximately 10V DC!

So far so good!

Your problem was possibly some oxide build up on connector J8 that has now gone since you have removed it and reconnected it.

Next, set your multimeter to read DC volts.

Connect the black (negative) lead of your multimeter to the black (negative) lead of the external big capacitor.

Measure the DC voltage at the following points:

Diode CR6 - measure the voltage on both wires of the diode with the red (positive) lead of your multimeter.

Diode CR7 - measure the voltage on both wires of the diode with the red (positive) lead of your multimeter.

Diode CR5 - measure the voltage on both wires of the diode with the red (positive) lead of your multimeter.

Diode CR1 - measure the voltage on both wires of the diode with the red (positive) lead of your multimeter.

Note that all of the voltages should read positive - with the exception of those for CR1 that should be negative. If you are using an analogue multimeter, you may have to swap the multimeter leads over again.

These readings measure what DC voltage is going into each voltage regulator (and should align with what you have already measured) and what is coming out of each voltage regulator. We are now checking that the voltage regulators are working correctly.

Dave
 
daver2 said:
I was just going to ask you to measure the voltage across the "big capacitor" and to verify that it is approximately 10V DC!

So far so good!

Your problem was possibly some oxide build up on connector J8 that has now gone since you have removed it and reconnected it.

Next, set your multimeter to read DC volts.

Connect the black (negative) lead of your multimeter to the black (negative) lead of the external big capacitor.

Measure the DC voltage at the following points:

Diode CR6 - measure the voltage on both wires of the diode with the red (positive) lead of your multimeter.

Diode CR7 - measure the voltage on both wires of the diode with the red (positive) lead of your multimeter.

Diode CR5 - measure the voltage on both wires of the diode with the red (positive) lead of your multimeter.

Diode CR1 - measure the voltage on both wires of the diode with the red (positive) lead of your multimeter.

Note that all of the voltages should read positive - with the exception of those for CR1 that should be negative. If you are using an analogue multimeter, you may have to swap the multimeter leads over again.

These readings measure what DC voltage is going into each voltage regulator (and should align with what you have already measured) and what is coming out of each voltage regulator. We are now checking that the voltage regulators are working correctly.

Dave
Click to expand...
Cr6 is 8v one side 5v the other
Cr7 is 10v /5v
Cr5 is 12.50 /20v
Cr1 is 11.35 /5v
 
They all look good as well. So far so good.

I assume the CR1 voltages are really negative (unless you swapped the probes around of course)...

My next question is regarding the memory expansion board.

I would recommend first trying to get the PET running as simply as possible. This should involve just transplanting the 6502 CPU from the memory expansion board to the PET logic board - observing anti-static precautions and making sure you insert the 6502 chip the correct way round into the socket.

Before you do this - is this something you feel comfortable about doing (bearing in mind if you insert the CPU in the wrong way around you could do some damage to it).

Dave
 
daver2 said:
They all look good as well. So far so good.

I assume the CR1 voltages are really negative (unless you swapped the probes around of course)...

My next question is regarding the memory expansion board.

I would recommend first trying to get the PET running as simply as possible. This should involve just transplanting the 6502 CPU from the memory expansion board to the PET logic board - observing anti-static precautions and making sure you insert the 6502 chip the correct way round into the socket.

Before you do this - is this something you feel comfortable about doing (bearing in mind if you insert the CPU in the wrong way around you could do some damage to it).

Dave
Click to expand...
I don't feel comfortable to do it i don't have a chip extractor and i just retried the cbm with the extension board still the same thing because as i know the cbm have a boot chime and also the processor seems very stuck in place and maybe i can buy a new one to place on the motherboard i juqt found one on ebay for 10 euros
 
That's why I asked.

So, if I understand you correctly, did you put the memory expansion board back into the PET and give it a try or not? If you did install the memory expansion board, did you measure the DC voltage across the large external capacitor to see whether it was correct this time or not?

If you want to buy a spare 6502 CPU that seems a reasonable price. Although the usual rules apply for buying from eBay...

You may also like to consider a ROM/RAM replacement board (e.g. https://www.hackster.io/news/the-ro...placement-for-your-commodore-pet-50d9077bdfcc and https://bitfixer.com/product/romulator/). I think both suppliers make a ready-built unit so ignore the 'kit' and ask the question.

Both of these cards permit you to replace the ROM and RAM of the PET with known good parts on the replacement board. You can also change the version of BASIC to the latest version. Both of these cards have in-built test tools (such as a NOP generator and my PETTESTER firmware) to help diagnose problems further. Can I suggest that you read up on these and consider them for later if we need them?

Dave
 
daver2 said:
That's why I asked.

So, if I understand you correctly, did you put the memory expansion board back into the PET and give it a try or not? If you did install the memory expansion board, did you measure the DC voltage across the large external capacitor to see whether it was correct this time or not?

If you want to buy a spare 6502 CPU that seems a reasonable price. Although the usual rules apply for buying from eBay...

You may also like to consider a ROM/RAM replacement board (e.g. https://www.hackster.io/news/the-ro...placement-for-your-commodore-pet-50d9077bdfcc and https://bitfixer.com/product/romulator/). I think both suppliers make a ready-built unit so ignore the 'kit' and ask the question.

Both of these cards permit you to replace the ROM and RAM of the PET with known good parts on the replacement board. You can also change the version of BASIC to the latest version. Both of these cards have in-built test tools (such as a NOP generator and my PETTESTER firmware) to help diagnose problems further. Can I suggest that you read up on these and consider them for later if we need them?

Dave
Click to expand...
I tried the cbm with the expansion board and it's still not working
And with the cable of the expansion and not the ribbon cable for the processor the big capacitor is still at 10v
 
Let's wait until you get the spare 6502 CPU then and continue our adventures.

You are aware of the pin numbering of the 6502 CPU and the orientation it must go into the PET logic board?

Dave
 
daver2 said:
I can purchase a 'reasonable' multimeter for less than 10 GBP each in the UK.
Click to expand...

The standard digital multimeter (DVM, DMM) is now a completely de-gentrified item. In the US, basic cheap Taiwanese models can be bought any day for around USD $5.00 or even less. A national discount tool retailer "Harbor Freight Tools" often issues coupons for a FREE meter with any purchase.

About ten years ago, a friend bought a handful of these cheap meters for around $3.99 each. Skeptical, we put them to the test, comparing readings with a couple of cal'd Fluke & Beckman meters from my bench. In all cases, the cheap models exceeded our expectations and tracked well with the standards.

About the only downside of the cheap meters was in their settling time. That is, they were slower to produce a stable reading. In some situations (like intermittently noisy or glitchy circuits) this can matter - but for basic, occasional use, it's not an issue.
 
My digital multimeter came free with a science magazine that my son subscribed to when he was in secondary school! He went into mechanical engineering for his University Degree, so donated the multimeter to me...

Yes, in the UK you can pickup cheap multimeters for GBP 2-3; but the figure I quoted was for (what I consider to be) a decent multimeter.

One of the 'concerns' I have regarding 'cheap' meters would be the safety aspects if you wanted to measure mains voltages or high(ish) voltages within a monitor (for example). I don't think the cheap probes are up to the job (personally).

If you are only going to use it for reading low voltage stuff - these are probably OK. Normally, a multimeter would include a fuse to protect it (and you) from harm. I don't think the cheap multimeters have a fuse either (it would increase the costs)...

Just worth bearing in mind - you do get what you pay for sometimes.

Look at the specifications for the meter and ascertain if it is the right tool for what you want it to do.

Dave
 
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