Thanks mlord - reading up on the pic 12F629, used in the 11GPS, the datasheets state the chip has an internal clock operating at 4Mhz. Looking at the other chips there appears to be buffer chips that depend on this clock to manage the flow of information. (My low level understanding of the relationship between the components in the circuit)
But based on your statement that an "external Oscillator device provides that clock for the PIC in this case", then replacing the 629 for a 683 would be an option. Now if the 4Mhz clock in the PIC 12F629 is utilized then the 683 most likely would not work.
I tried rewriting the 12F629 chip, the write was successful, but the operation still fails - error 16 and 17. Recall, I can replace the entire Serial Board with a known working one, and the 11GPS scope regains full function and operation. So something on the board is failed. The only remaining component is the PIC 12F629, and my trouble shooting does not point to an internal failure of the PCB itself. My testing shows continuity and no shorts based on what I see operation should be from the traces and schematics.
Reading various articles I picked up some information about calibrating the internal oscillator. See here: http://picprojects.o...recal/recal.htm
I also read articles stating that the program code, firmware, has instructions embedded concerning the same.
My current working theory is the Pic 12F629 was damaged - specifically the 4Mhz oscillator piece. So the chip can be read and written to, but the oscillator component is damaged. Again, based on reading, this oscillator component is fragile and a voltage spike could cause harm. I don't know if the linked article above, recalibration utility, is an option or relevant. I would assume the firmware should have the code to set the correct parameters for the chip.
So, the big question, if I replace the Pic 12F629 and program it with the correct firmware will anything else need to be done? Is the calibration issue a non-issue in this application?