I was printing on my IIISi tonight and, between jobs, it switched from
working normally to displaying "50 SERVICE" (with the "50" flashing)
and not accepting print jobs.
I don;'t know the IIISi, but on all the HP (and Canon) laser printers
I've worked on, error 50 is a fuser problem. Either the fuser got too
hot, or more likely it didn't get hot enough.
Power cycling doesn't help.
There is a protection circuit in these machines (certainly the ones I've
worked on). If there's a fuser error, the machine will not work unless
it's been turned off for soemthing like 15 minutes (this is so if the
fuser has rteally got too hot, it's got time to cool down). There's a
capacitor on the DC controller board you can discharge to clear this
(very useful if you know the fuser is not too hot...), but I have no idea
if it's the same on the IIISi, or where that capacitor is.
Anyway, the most common cause of this is a problem with the fuser heater
itself. On the printers Iv'e worked on, this is a tungsten-halogen bulb
down the middle of one of the fuser rollers. If you extract the fuser
assmebly, it's generally fairly obvious where the lamp connections are,
and it's easy to test the lamp filament for continuity. Most of the time
when you get this error, the lamp is open-circuit, you need to replace it.
There's also a thermal swtich in series with the lamp inside the fuser.
This isthe final protection method, if things go badly wrong this will
cut the lamp power and prevent the thing seriosuly overheating. You can
test this too, it should show a dead short.
If all that's OK, then the proeblem is with the controller circuitry. I
could easily talk you through the CX and SX stuff, I've worked on them,
I've done component-level repair on them. But I suspect yours will be
I've done a little poking around, but haven't
managed to find a service
manual for the silly thing. Bitsavers has only one file under
The servie manual will certainly be a boardswapper guide, but it might
show interconnections, etc.
Have you tried the Australian HP museum? There are some printer service