Lexmark T64X -- Redundant NVRAM

Lexmark's early Optra T printers experienced a lot of non-volatile RAM (NVRAM) failures ("954 NVRAM Failure" error message). There was only a single NVRAM IC in the machine and it was on the Engine Controller PCA, so that was straightforward enough -- replacing the Engine Controller PCA was the fix.

I imagine all those failures were what led Lexmark to build redundant NVRAM into the T64X models. Those machines all have three NVRAM ICs -- one on the System PCA, one on the Interconnect PCA and one on the Control Panel PCA. With NVRAM data existing in triplicate, an error from one NVRAM IC can be worked around and the printer can go on operating normally, instead of succumbing to a fatal error as the early Optra Ts did. All well and good, but it introduces a little servicing wrinkle that can make for some costly, clumsy repairs.

When any one of those three PCAs is replaced^[1] for whatever reason, once initialized in a given machine, the replacement PCA is 'married' to that machine. It can't be used elsewhere; it can only stay where it is, or go back to the factory.

That can be a bit sticky when you have a coin-toss/guesswork troubleshooting situation; e.g. a printer that powers up with a blank display.

On the face of it, the fault is probably in the Control Panel PCA, but it's entirely possible for it to be in the System PCA. All you can do in that situation is quote the customer for the total cost of replacing both^[1] parts, because that's what you may end up doing to fix the printer.

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[1] Only replace one item at a time; the printer must have access to two of its original NVRAMs to be able to initialize the replacement part. Replacing two items at once will render the machine unrecoverably inoperative. Each part installed must immediately be put through a full power-on reset (POR) routine.

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