Does anyone know of any issues that might be preventing some PIC16LF819's
being reprogammed in-circuit, using a Microchip ICD2 programmer?

I have 20 boards each with a PIC16LF819 (SOIC) soldered in. They all
programmed without any problems first time around. I then needed to
reprogram them and 17 reprogrammed fine, but 3 failed. In fact they fail at
the first of the programming cycle, the Part Erase. Even though the erase
reports that it succeeded, it takes a lot longer than it should (5 seconds
instead of few hundred ms) and a subsequent blank check says it failed.
Everything I have tried so far has not got them to reprogram.

The config bit settings as shown by MPLAB (v6.60) for the original and
reprogramming are:
  Oscillator:           INTRC-RA6 is Port I/O
  Wathdog Timer:        Off
  Power Up Timer:       On
  MCLR Select Bit:      RA5 is MCLR
  Brown Out Detect:     Off
  Low Voltage Program:  Disabled
  Data EE Read Protect: Disabled
  Flash Program Write:  Write Protection Disabled
  CCP1 Mux:             RB2
  Code Protect:         Enabled - All protected

I have desoldered all the peripherals components in case they were causing
the trouble. So now the only connections to the Vpp, PGC and PGD pins are
from the board's programming header, but the reprogramming still fails.

I've buzzed through and checked for shorts but no problems found.

I have tried selecting power from the ICD2 and also power from the board -
no luck erasing/reprogramming either way.

Checking the signals on a scope: Vdd is 5V (if powered from the ICD2) or
3.3V (if powered from the board); During programming Vpp reaches 13.5V (rise
time of 70ns approx); PGC and PGD both produce good squarewaves between 0V
and Vdd.

I've tried a couple of other ideas I've come across - adding a pull-down of
1k to the Vpp line, and also a pull-up of 1k to the same line (on a
different occassion) but with no success.

Could anyone please offer any suggestions as to how to get these
PIC16LF819's to erase and reprogram? BTW - the codespace is totally full,
otherwise I guess I could include a bootloader to get around this. Also, if
another programmer is likely to work better for this than the ICD2 then I'm
willing to get one.

Very many thanks,

James

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