"My HP Laserjet III is giving a "50 Service" error. So something is wrong with the fuser. But the lamp is not burned out. Also, the fuser roller is pretty clean.
When I turn on the printer, the light in the fuser comes on for a second. Then there's a click from the power supply (or around there), and the light goes off.
The 05 Self Test message comes up.
Then Warming up (takes a while).
Then, both online and page feed lights go out and "50 Service" appears.
The power supply and fan are working and the ozone filter is clear."
(From: Geir Knutsvik (firstname.lastname@example.org).)
What about the fuser? Does it make heat? I have in some cases have faulty opto electronics for sensing paper and drawers result in Error 50.
In worst case it cold be the main pcb ...expensive... check dc controller.
(From: Mark Wolfe (email@example.com).)
5 bucks says it's Q101 in the power supply (crosses to NTE 5620). I've seen quite a few where this was the problem. Check the power connector at the right end of the fuser, it's under a plastic cover. There should be about 115 VAC there during the warm up, you'll have to stick something in the cover open switch to get it to power up. If there is 115 VAC, it's the lamp in the fuser. If there isn't 115, it's save to say it's Q101 which is the triac that supplies the fuser. Get a new heatsink with the new triac. Cost here with tax to fix the problem is $7.07 + my labor. :)
(From: Terry (firstname.lastname@example.org).)
This error can be caused by missing 24 v, bad Thermistor, Fuser Bulb or Thermoprotector. Replacing the fusing assembly is quite easy by removing the 4 silver screws that secure it.