Lexmark C782 MFP with the message insufficient memory to support scanner operation. On start up the memory count goes to 512mb. The total memory required for scanner to operate is 708mb according to Lexmark. Could this be a memory card or formatter(system board as Lexmark call them)? If I unplug the scanner from the system board the base machine works fine. As the memory card and system board cost around ?00 I don't want to purchase them without being sure they are at fault. Many thanks in advance for any advise you may have.
these memory errors in the last months, seems that Lexmark used bad chips for both system memory and the optional DIMM required for the MFP.

If the machine counts up to 512MB Memory, the 256MB soldered on the system board are unusable. You could check the RAM by removing the optional RAM-DIMM, the Firware card and the PCI-Card which connects to the Scanner.
(In most cases, i was not able to reach the RAM-Test since the printer would report a "960.xx Memory Error" at power-on.
"960"-Errors represent the Onboard-RAM, "961" Memory in Slot 1 and so on ...)

Press both Arrow-down and Arrow-right keys while switching the printer on. Release keys when the readable text is displayed.
In the following menu scroll to "Hardware Tests", enter the sub menu, scroll to "DRAM Test" and activate the Test by pressing the "Enter"-Key. The printer should reboot to the RAM-Testmode and displays two numbers, representing test loops and a fault count.

In your case you should replace the System Board. Make sure to buy a new part. Used boards contain system data from the machine they were used in and are unusable as replacement parts.