20 Jul
2006
20 Jul
'06
3:59 p.m.
Philip Pemberton wrote:
This is an SX engine, isn't it?
If so, there are _4_ PCBs involved :
The one on the end of the fuser, which simply connected the thermistor to
the cable harness. The other stuff on that PCB has nothing to do with the
temeperature contorl
The DC controller board, which monitors the resistance of the thermistor,
and procduces the fuser drive signal
The protection board which disables the fuser if something goes seriously
wrong
The AC input board which contains the fuser control triac and protection
relay
In any case, I find thinking about which boards are involved to be the
first step to board-swapping, which is not a route I want to take. I
prefer to think about the signals involved, to monitor those, and then
check back to components.
Don Y wrote:
There are two different PCB's involved in dealing (directly)
with the fuser. One supplies power to the lamp. The other
monitors temperature, etc. OPen the rear door. Apply power. Wait 3 or 4
seconds (not TOO
long else the error sets and you have to power down for several
minutes for it to clear itself). You should see the lamp light
up in the first few seconds or so.
Nope. The fuser's completely off.
The supply has an overtemperature cutoff device that breaks
the circuit to the filament. If you don't see 24V at the
lamp, this could be open (i.e. broken).
On every laser printer I've ever worked on, the fuser lamp runs off the
mains. Not off 24V or anything like that. And yes, it's directly on the
mains, there is no isolating transformer (the control signals are
isolated by optoisolators and/or relays)
Also be warned that there are snubber networks across the relay and
triac. If the fuser is open (or removed) you will see mains voltage
across the connnector on the AC block even when the fuser should be
turned off, since your voltmeter is so high an impedance that the
snubbers will easily pass enough current to drive it.
There is a thermistor located near this cutoff device
that
performs temperature *control*. It obviously relies on
a processor (hence is not a reliable means of preventing
OVERtemperature cutoff :> ).
I have a note (to myself) about replacing an upper fan
to fix an intermittent "50" error. You might want to check
Presumably becuase the thing was overheating?
if the fan is bound, shorted, etc.
The bearing on the opposite side to the motor is known to fail. These
fans are easy to take apart, then you can clean up the parts and
reassemble with a bit of light oil on the bearings. It will at least tell
you if the fan was the problem.
If NOT,
power off (before the error sets). Wait a few seconds
(no, not a few MINUTES, just a few seconds ... 5 or 10) and then
power on *again*. See if the light comes on this second time...
No activity on the second attempt either.