acenewman
Experienced Member
Picked up my first PET a couple weeks ago. Have things cleaned up and am starting to troubleshoot it now. Currently it has garbled text at the top of the screen and just the @ symbol filing the remainder. You can see a few photos here
https://www.dropbox.com/sh/sbkm2grdydvqs7t/AABQNj_LfGed-4QSgNKO-Eiua?dl=0
So far this is what I have checked to troubleshoot the CPU using an oscilloscope:
Pin 40 RESET is high
Pin 2 RDY is high
Pin 6 NMI is high
Pin 4 IRQ is high
Pin 37 & 39 both have a 1 MHz square wave
Pin 7 SYNC signal seems like it may not be right. My understanding is that it should be low and pulse high. Mostly it looks like a low signal with some noise in it to me. Being kind of new to this I checked the same signal on one of my working Apple iie computers and it is very different. I also went as far as to swap the PET processor into the Apple and it booted up just fine. So the processor seems to be fine.
Looking for ideas on where to go next on the SYNC signal? Also I forgot to mention I did start by checking all of the voltage rails and they were right on 5, -5 and 12 volts at the memory sockets.
Thanks for any insight you can provide, Chris
https://www.dropbox.com/sh/sbkm2grdydvqs7t/AABQNj_LfGed-4QSgNKO-Eiua?dl=0
So far this is what I have checked to troubleshoot the CPU using an oscilloscope:
Pin 40 RESET is high
Pin 2 RDY is high
Pin 6 NMI is high
Pin 4 IRQ is high
Pin 37 & 39 both have a 1 MHz square wave
Pin 7 SYNC signal seems like it may not be right. My understanding is that it should be low and pulse high. Mostly it looks like a low signal with some noise in it to me. Being kind of new to this I checked the same signal on one of my working Apple iie computers and it is very different. I also went as far as to swap the PET processor into the Apple and it booted up just fine. So the processor seems to be fine.
Looking for ideas on where to go next on the SYNC signal? Also I forgot to mention I did start by checking all of the voltage rails and they were right on 5, -5 and 12 volts at the memory sockets.
Thanks for any insight you can provide, Chris