Quote Originally Posted by Russ Kincaid View Post
... and tried to program a 12F675 that had already been successfully programmed. ...
Curious ...

Do you know if the program that was already loaded in it was using the Internal Oscillator with MCLR disabled?

I've had some difficult times trying to reprogram 675's and F88's after that scenario.
But I was able to get them back by turning on power to the chip at just the right time in the programming sequence. Took 10-15 or more tries each, but did get them all back.
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