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  • dave_m's Avatar
    December 4th, 2017, 01:05 PM
    I agree we should do the easy stuff first that will give us some data points. Yes, with the 6520 PIA's and the 6522 VIA removed, if all else is...
    15 replies | 947 view(s)
  • dave_m's Avatar
    December 4th, 2017, 12:26 PM
    KC, I wonder what problem could get good ASCII characters on the screen as the voltage slowly decays away? Out of spec power supply voltage? With a...
    15 replies | 947 view(s)
  • dave_m's Avatar
    December 4th, 2017, 10:06 AM
    From the display indications at turn-off, it seems like the main board is almost working. Check all the DC voltages. All the DC voltages can be found...
    15 replies | 947 view(s)
  • dave_m's Avatar
    December 3rd, 2017, 03:30 PM
    Pin 9 of the CPU is the Least Significant Bit (LSB) address line and should be pulsing if the PET is executing instructions. So on a DC voltage...
    27 replies | 2368 view(s)
  • dave_m's Avatar
    December 2nd, 2017, 10:39 PM
    Ian, After the voltage tests, since it seems that your ROMs are on sockets, for a quick and dirty test, replace the kernal ROM at UD6 with a 2532...
    29 replies | 980 view(s)
  • dave_m's Avatar
    December 2nd, 2017, 11:36 AM
    I know Commodore PET main boards are not considered 'High Reliability" electronics, but in the aerospace industry, if a board had been cleaned using...
    13 replies | 480 view(s)
  • dave_m's Avatar
    December 1st, 2017, 11:39 PM
    Mike, I can always count on you for great ESD safety tips! :) -Dave
    13 replies | 480 view(s)
  • dave_m's Avatar
    November 30th, 2017, 10:05 AM
    Frank, I'd have to agree. With a Commodore, leave well enough alone. Some collectors have a fascination with 'pretty' PETs. I'm just glad mine...
    13 replies | 480 view(s)
  • dave_m's Avatar
    November 29th, 2017, 01:25 PM
    Alec, Not sure I would use WD40. I would use Isopropyl Alcohol 90% + pure to clean the board. Any excess will quickly evaporate. You do not want...
    13 replies | 480 view(s)
  • dave_m's Avatar
    November 27th, 2017, 03:41 PM
    Wow, this is very tricky. Something on the address or data lines would cause more problems than you are seeing. Is it possible that your highly...
    8 replies | 251 view(s)
  • dave_m's Avatar
    November 27th, 2017, 02:36 PM
    Are the PIA 6520 chips on sockets? If so, replace G8 (PIA#1). The lines for cassette #1 and the Vertical Sync interrupt circuit are in that chip.
    8 replies | 251 view(s)
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About MikeS

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About MikeS
Location:
Toronto ON Canada
Interests:
Cromemco,S100,PET,AIM65,PC
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Geezer

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