Panasonic KX-P8420 - Manual (Page 195)

195
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To replace the printer controller board:
1 Align the printer controller board with the groove on the
back of the printer and carefully slide it back inside the
printer.
2 Tighten the two thumbscrews on the printer controller
board that you loosened earlier, using a cross-point
head (+) screwdriver.
3 Plug in the power cord and reconnect any cables to the
back of the printer.
Printer controller board