Panelview 900

Panelview Part #: 2711-K9A8, that communicates via DH+ to a SLC504.
There are two PV's on the network. One has lost its application. Downloaded the application and all works but on reboot the application is lost. There are error messages on powerup but none correspond to anything in the manual. Most the time it states "2016 application file has errors". Then in the setup menu it states that no valid application is available...
There's a chip DS1643-120 on the main board. We took the chip from the working PV and problem seems to be gone. We then took the same model chip from another PV (PV 900 with DH485) and this did not work.
The chip is a nonvolatile RAM. I wonder if they are specific to each PV model?
What is the best way to repair this?

The DS1643-120 is a small nonvolatile timekeeping RAM, so it's probably the system's clock. How exactly it's involved in the validity check for the application file, I can't say.

It's possible that chip is also where the PanelView model is stored, which the OS would check to be sure that the installed runtime firmware and the installed comms daughtercard are consistent and correct. That would explain why a chip from a DH485 model terminal didn't work.

You could try to read the contents of the chip in the DH+ terminal and write it into a new chip byte-by-byte, but you're already far past what a typical repair shop would try to do for these terminals.

Update:
We ordered a DS1643-120 nonvolative RAM and installed it on the defective Panelview. Loaded the application, power cycled and it kept the program!!! I already had a company lined up to read data from another working RAM chip and program the new ones. Sometimes we are lucky. We ordered the new chip from Radwell, they are available on ebay but with long delivery time. These RAM chips are no longer in production so battery life will be an issue.

It might sound stupidly simple but I wonder (if you hadn't tried already) would a reflash of the firmware have done anything? Perhaps it plays some part in this chips operations and may have become corrupted?

Presumptious on my part though.

I have a couple of old PanelView 900 terminals knocking around. I might open one and have a nose around for this chip. I don't think I've ever had one open before?

Regards,
George