Panasonic GP6DU Technical Manual page 117

For all units requiring service, if the serial number is below YB4550001, APPLY
THIS EEPROM DATA UPDATE regardless of the original failure or customer
complaint.
If this EEPROM update does not resolve the listed symptoms, a replacement DG
board may be needed.
Call Panasonic's Tech Support line at 1-800-743-2335 for assistance and/or
a board authorization #.
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