David, I found the following entry @
http://www.anatekcorp.com/faq/printer.htm

HP laserjet3 printer has error 50.

Usually I replace the triac or the two resistors connected in the ac power module.   This does not solve the error. I have four other power modules with same problem.


Error 50 implies a Fuser error. Besides faults in the AC power module, in the fixer assembly, the fuser lamp itself, or the in-line thermal fuse, or the thermo-switch, can go open, so check for continuity (low-ohm's) through these.   Sometimes, unfortunately, the DC Controller boards on the LJ 3's can fail and give a type 50 error, and need replacing. But before replacing, first check the two cables to the DC controller, at J206 & J208, and the solder on the connectors.  However, if your problem was localized to the AC power board, after all, then besides the Triac and those two resistors, check the triac driver optoisolator IC, and look for any bad solder on the connectors. Also, if you see any of those bright green Sony electrolytic caps anywhere, check if they leaked. If so, you need to clean up well under them, repair any board damage, and replace the cap. To clear a type 50 error from the machine, you must power-off for at least 15 minutes. END

Additonal Printer Resources:
http://www.partsnowinc.com/
http://outfield.external.hp.com/cgi-bin/spi/main

Good Luck!
Erik Hundrieser

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