CALL SERVICE ERROR 53

On the HP Laserjet 4L/4ML/5L this error is indicated by the data light on and all others off.
4L/5L
1. Error found in RAM(or ROM, 5L only) - power cycle the printer
2. Defective or incompatible memory card - remove card and power cycle the printer
3. Defective formatter PCA - replace
On the HP Laserjet 4/4+/4Si/4V/5/4P/4MP the 53.XY.ZZ error code is decoded as follows:
53 (XY-ZZ) where

X- Hardware Type:
0 = ROM
1 = RAM

Y - Hardware Device:
0 = On Board RAM/ROM
1 = SIMM Slot one
2 = SIMM Slot two
3 = SIMM Slot three
4 = SIMM Slot four
ZZ Error number:
00 = Unsupported memory
01 = Unrecognized memory
02 = Unsupported memory size
03 = Failed RAM test
04 = Exceeded max RAM si
ze 05 = Exceeded max ROM size
06 = Invalid SIMM speed
07 = SIMM reporting incorrect
08 = SIMM RAM parity error
09 = SIMM ROM mapped to an unsupported address
10 = SIMM address conflict
11 = ROM out of bounds
12 = Could not make temporary mapping
*A 53.1y08 error is generated in LJ4+ memory is installed in a LJ4 The 53.03.01 error code is decoded as follows:
A ROM error in SIMM slot three with unrecognized memory.

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Error 54IID, IIID Only: Duplex Feed Error
1. Check Duplex Shift Plate for correct position and operation
2686 A/D Only: Main Motor Stall
1. Paper Tray is overfull
2. Fuser drive gears bent of locked up