can i try to desold some logic to test with logic tester?If you are using the Kernal ROM with my PETTESTER it shouldn't matter which version you use - because my PETTESTER ROM is designed to work with any known PET Kernal ROM.
The only reason my PETTESTER wouldn't work (and the CPU stop executing instructions) is if the Kernal ROM contents became corrupt (or read incorrectly). In this case, this is only valid for a few bytes of the Kernal ROM.
If you have put this Kernal ROM into another (working) PET - and my PETTESTER correctly identifies the checksum as being correct - then this is as good as it gets. Of course, it could be the IC socket the Kernal ROM is plugged into - you were responsible for replacing this item, soldering it and checking the pins for continuity.
Ditto for the PETTESTER ROM itself (and the associated IC socket).
If you transplant the Kernal and PETTESTER ROMs from this (faulty) PET and try them in a (working) PET and they work - then they are good...
Dave
How can i do to test this please??The only way it COULD fix the problem is if it is producing noise on the power lines or is drawing a high current - but you should have tested for this as the very first thing you did.
Time to leave white flag i suspectSelect AC volts on your oscilloscope (a low voltage range) and 'scope each of the power lines.
Keep reducing the volts/div knob until you start seeing noise - noise will always be present - and measure the peak-to-peak value (the highest and lowest voltage). Adjust your oscilloscope trace level to be in the middle of the oscilloscope screen. Positive voltages are then higher than the middle of the screen and negative voltages are lower than the middle of the screen. 0V (of ac noise) is in the middle.
Adjust the oscilloscope timebase to also obtain the maximum amount of noise. Noise appears at certain frequencies - so having your timebase set too fast or too slow will miss it. We are looking for the "inverse goldilocks scenario" (i.e. the worse noise).
There are multiple power rails (2 off +5V, +12V and +5V). I would suggest measuring them all now - although the two +5V supplies are the only ones that would actually affect us with the PETTESTER.
Look for hot devices to see if any device is passing a lot of current. The total can't be excessive, otherwise the voltage regulator(s) would have shut down.
Dave