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Toxic
07-19-2021, 09:00 PM
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
07-19-2021, 09:08 PM
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
07-19-2021, 09:24 PM
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
07-19-2021, 09:27 PM
Toxic just an idea:
https://www.copytechnet.com/forums/konica-minolta/59512-bizhub-pro-1200-code-c-3906-a.html?59512=#post261286

Toxic
07-19-2021, 09:36 PM
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
07-19-2021, 09:49 PM
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
07-19-2021, 11:38 PM
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
07-21-2021, 11:29 PM
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
07-22-2021, 12:03 AM
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
07-22-2021, 01:51 AM
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. =^..^=

Toxic
09-29-2021, 12:58 AM
Another update...
Few days ago i replaced new th4 sensor, same result,periodically c-3906,maybe little less more occurence than before but can not be sure about that.
Removed back cover, conected voltmeter and current meter on lower fuser lamp L3 and observe while printing.
Everything looks ok, lamp getting about 230v and draw about 1.4A, i was assuming some wiring or conection to lamp is lossing in some moment but that is ok.
This also should exclude thermostats, connector, lamp, lamp wiring,...as a culprit.
In continuous print L3 have about 50 seconds ON and 7 seconds OFF working cycle.
One time i manage to catch moment before C-3906 , L3 was continuously working for over 120 seconds before get coded.
At the end my suspicion is more abot PRCB than some hardware problem in fusing unit, AC board...
I will let it go for now , 3906 comes once over 1-2 days so it is not so much hassle to reset.

allan
09-29-2021, 01:24 AM
Is it possible to take the fuser to another machine?

Toxic
09-29-2021, 01:33 AM
Good idea and i would try that but dont have another machine near.

tulintron
09-30-2021, 04:02 PM
Another update...
Few days ago i replaced new th4 sensor, same result,periodically c-3906,maybe little less more occurence than before but can not be sure about that.
Removed back cover, conected voltmeter and current meter on lower fuser lamp L3 and observe while printing.
Everything looks ok, lamp getting about 230v and draw about 1.4A, i was assuming some wiring or conection to lamp is lossing in some moment but that is ok.
This also should exclude thermostats, connector, lamp, lamp wiring,...as a culprit.
In continuous print L3 have about 50 seconds ON and 7 seconds OFF working cycle.
One time i manage to catch moment before C-3906 , L3 was continuously working for over 120 seconds before get coded.
At the end my suspicion is more abot PRCB than some hardware problem in fusing unit, AC board...
I will let it go for now , 3906 comes once over 1-2 days so it is not so much hassle to reset.If it overheats, the lamp is ok.

TH4 sensor ok.


PRCB receives signal from TH4 and reports error when it occurs. PRCB ok.


CN213 from PRCB sends TH4 signal to ACDB to turn off L3.


I would look the other way. ACDB

tulintron
09-30-2021, 04:04 PM
Someone doesn't turn off L3 when they should. But the order to turn off comes

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