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richard at home
June 25th, 2014, 02:10 AM
Hi All,

Just started looking at my first PET.

It's a 3032 and there is nothing on the display.

Power is all good

Initial probing showed nothing going on with the video circuit.

Next I took a look at the processor.

All address lines are high!

Clock is ok, reset high.

IRQ is permanently low.



SCRATCH THAT!

As I was typing this, I just re-powered to see when IRQ went low and READY has just appeared on the screen...:)


So maybe there is a dodgy socket somewhere....

richard at home
June 25th, 2014, 02:40 AM
Hmmm...

It appears that UC7 6520 (keyboard interface) is generating the IRQ and sometimes it doesn't get serviced, so the system hangs.

Sometimes is does get serviced and I get a display.

The display is odd in that it's showing random BASIC syntax errors.

The ROMs are homebrew EEPROMS of some sort, in positions UD9, 8, 6 and 5. Nothing in UD7, 4 or 3.

richard at home
June 25th, 2014, 03:53 AM
Looks like UD7 being missing is a problem... Need to track down one or blow my own...

dave_m
June 25th, 2014, 07:51 AM
Looks like UD7 being missing is a problem... Need to track down one or blow my own...

The TI 2532 EPROM is a direct replacement for the PET 4K ROMs. The more available 2732 EPROM will need a simple adapter to match the ROM pinouts.

Note that many new device programmers do not support the 2532 which requires a 25V programming voltage.