I am looking at an older HP LaserJet 3P printer that will not print for a
friend. I do not have a service manual, but figured I would give this a
shot.

Symptoms: Plug in and power on the unit and it runs through its "05" self
test, then the green "on-line" light illuminates and the printer is in the
"ready" mode. If you try to send a job to the printer, the green light
flashes indicates it is receiving the file, but then the LCD panel indicates
an "error 52".

I disconnected the computer and attempted to print the self test page by
depressing the on-line (to go offline), then simultaneously depressing the
"alt" and "test" buttons. This then goes through the same 05 self test
followed by an 06 print test. At the conclusion of the 06 print test, you
can briefly hear the page feed motor and then the "52 Error" message is
illuminated.

I've checked the HP support web site and it indicates that the 52 is a
temporary internal error and that pressing the "continue" button may clear
the error. But, in my case, it tries to go through the test again, but you
get the same result.

My Hypothesis: I speculate that the sheet feed mechanism is not working
properly since no paper is ever picked up from the front paper tray. I have
found a small solenoid in the front side cover that appears to lock out the
paper pickup cam from rotating and selecting the sheet. I believe that it
is not getting a signal (it measured 120 ohms across the input to its coil
so I believe it is OK) to disengage the lock and allow the cam to rotate and
pick up the paper. (The gear that drives this is turning, but the latch
never disengages since the coil never energizes during the cycle.

I believe that the printer processor board and mechanics are good and that
the 05 self test passes properly. I think that the 52 error comes when the
printer does not see any paper ever get advanced since it expects one. Does
this make sense?

My next step is to look at the control board and try to trace the paths from
the solenoid pins on the connector to a drive transistor. Does anyone have
a schematic and if so could they point me to the transistor number and type
or provide test voltages so that I can determine what is happening.

Also, if anyone has seen this type of error on this printer before or has a
more likely root cause, I'd love to hear your thoughts. Without a service
manual I know I'm working in the dark, but do believe that the problem seems
to be around the electronics driving the paper feed/pickup solenoid. Thanks
in advance for your help.

Bob Shuman