C-3906 Pro 1100

[Toxic]

Mess with C-3906 on 1100 almost whole day.
Machine power up always ok and idle but every time after about 200-300 A4 printed sheets throw up C3906.
Lower part of fusing unit where is heating roller looks like hotter than it should be in my subjective opinion.
Removed and cleaned TH4 sensor, no result.
Put another TH4 sensor from 950 (99% working), same result.
Lamps testing resistance seems to be ok.
Removed back filter box to make more air circulation, no result.
Removed back cover, check i/o check rear fan behind fusing, both low/high speed runing.
Tested all fusing sensors in i/o check, all show reasonable readings 150-180 celsius.
Checked wiring from sensor to fusing back connector and to PRCB, everything looks ok.
When testing both sensors on lower heating roller both shows almost same resistance like expected with cold or hot fusing unit.
I try to unplug TH4 and power up, instantly get C3906.
No more ideas for now , tomorow i will get new TH4 sensor but i doubt it will solve problem.

Anybody see something like this?
Machine have about 6 mil and i did not maintain it till recently.

[blackcat4866]

The only time I've seen the C3906 is when my enduser sprayed an entire can of air into the fuser, thoroughly freezing the thermistor. I'm surprised that there weren't shattered pieces of heat lamp everywhere, but everything survived, just needed the DIPSW reset.

A lot more common is C3903, which can be the modular connectors getting shattered, and making poor electrical contact. I've replaced at least 3 sets of those modular connectors. It's usually pretty obvious once you look at the connectors. =^..^=

[Toxic]

You mean on connector on the rear of machine where fusing connector slide in?
I checked both connector, machine side removed and look from inside for bents contacts, did not see anything strange.
Somehow i doubt it is connection problem, if so error will be intermitent and i have almost same pattern when error will come up, after 200-300 prints.

[tsbservice]

Toxic just an idea:
Bizhub Pro 1200 code C-3906

[Toxic]

Thank you my friend, you are never bothered to search for everybody but i already google for this error and read that topic.
Tomorow i will try to clean that fan just in case altough it is not so dirty.

[tsbservice]

Thank you my friend, you are never bothered to search for everybody but i already google for this error and read that topic.
Tomorow i will try to clean that fan just in case altough it is not so dirty.

I'm stuck with my lack of experience. Nevertheless I will never left stone unturned in my desire to help fellow tech.

[blackcat4866]

You mean on connector on the rear of machine where fusing connector slide in?
I checked both connector, machine side removed and look from inside for bents contacts, did not see anything strange.
Somehow i doubt it is connection problem, if so error will be intermitent and i have almost same pattern when error will come up, after 200-300 prints.

The C3903 did clear, then re-occurred after a paper jam (customer had to open/close the imaging drawer). For a couple weeks it was every other day. =^..^=

[wjurls]

Recheck the lower heater. Could be a bad filament that is losing connection once it heats up. It happens. If you remove the front fuser cover and cheat the door you should be able to see if the lamp is coming on.

We've seen a number of hard C-3906 failures on 951's that end up being the PRCB.

[Toxic]

Update:
Next day after my last post i removed and cleaned rear fan behind fuser (although it was not so dirty), removed lamp 3, visual check, looks ok.
For whole day no error and done about 15k prints without problem.
Put back rear machine cover and filter box.
Today get 3906 again after first 200 prints, just reset without touching anything else and after that done about 15-20k prints with no problem.
Got new sensor but not installed yet, i wish to track problem and this is very interesting and misteriously for me.

@wjurls
Good idea, i can see upper lamps from back and i will try that but problem now is error does not get so frequent, only if it starts again to throw error every few minutes.

[blackcat4866]

Just to confirm, yes the machine will initialize with an open lamp, but may go into long warmup cycles. Also, an intermittent thermostat can give these effects. They're not that expensive, and can react differently under electrical load, than when they're cold on the test bench. =^..^=