You might not have fried them after all.  I have heard that one of the ways
MicroChip increased the security of their devices is to increase the UV
exposure needed to erase the configuration bits.  This is because some
enterprising souls figured out how to manipulate the chip voltage and
erasure techniques to clear the code protect bit while still leaving the
code itself intact.  By making the configuration bits much harder to erase,
the contents of the program memory will be gone by the time the protect bit
is cleared.

Anyway, it could be that you just need to increase your erase time over
what you had been using, since your programmer might report that device is
not blank even if only the configuration byte is non-blank.

If you are using old (pre-used) chips that you KNOW don't have the new
security features, your chips might still be OK.  UV light sources weaken
with age, and it is possible that all you need to do is increase the erase
duration to compensate.  If you find it take a lot longer to erase chips
now, you might want to replace your UV tube.

Finally, check for dirty quartz windows on the chips themselves, and maybe
(this one is a stretch) the chips are just getting harder to erase with
age.


CIAO - Martin R. Green
elimar@bigfoot.com

----------
From:   unknown667[SMTP:unknown667@HOTMAIL.COM]
Sent:   Wednesday, September 10, 1997 12:51 PM
To:     PICLIST@mitvma.mit.edu
Subject:        frying a PIC

For some reason I'm unable to erase my PIC16C74A.  I've got a Datarase II 4
chip UV eraser, which has been working fine, and the Microchip umm...
quickstart or something programmer.  Suddenly, today, I find that when the
chips come out of the eraser, the programming software I'm using
(MPS16C.EXE) reports that the chip is not blank.  Any ideas on how I could
have fried the chips?

---
Unknown