The LaserJet III is a robust and reliable printer; a fine example of
Hewlett Packard engineering. A few resources
are collected here to help with repairs. Flemming Gottsche made
a schematic of the
AC power supply to the fuser and kindly
allows it to be published here as a pdf file available by http. The
document is copyright (c) Flemming Gottsche, 2000-present. For
permission to publish the diagram or make any commercial
application ask Flemming. Use a Web search to find a current
address.
Harald Zech made a thorough study of a subtle failure of the
printed circuit board RG1-1438. Harald's
Troubleshooting: HP LaserJet III Malfunction ``50 SERVICE''
is also a pdf document available by http. The document is
copyright (c) Harald Zech, 2005-present. For permission to publish
or make any commercial application ask Harald.
His eaddress is specified at the end of the document.
With power on, the LaserJet III keeps the fuser at operating
temperature. To prolong the lives of the power supply and
fuser, powering down at the end of the working day is recommended.
Capacitor C153 and the triac Q101 have been replaced in
machines here.
Best viewed with a Web browser.