C-3721 (fuser over-temperature) - How is it related to door adjustment?

[John Kaufmann]

Bizhub C280, error code C-3721, [Service Manual drops the hyphen: C3721], one of three codes for "Fusing abnormally high temperature detection":

• C3721 (Center of the heating side)
• C3722 (Edge of the heating side)
• C3723 (Pressurizing side)

Fusing unit appears normal, certainly not over-temperature. (After resetting the code, I set fuser temperature to its lowest limit. It still threw the error after restart.)

But the Service Manual's 2nd troubleshooting step (after checking the fusing unit installation) is "Check the open/close operation of the right door." What is that about? That is consistent with other problems the machine is having (duplex jams because duplex transport sensor fails to trip, because door is out of adjustment), but I don't see the connection. How is fuser over-temperature related to the door?


Related question: getting the door closure adjusted properly seems impossible. On closer inspection, it appears that the door frame itself is out of plumb, as if the right rear corner took an impact causing geometry distortion (though I'm not sure how functionally significant it might be). Have you ever seen this?

[Blizzoo]

The operation of the right door has a role in actuatate the fusing lamp power after is closed.Usualy a door that is not fully closed or not actuatate that switch will throw warm up failure not abnormal high temperature.


After inspect parts manual i think that sw is the number 5 in attach.
switch.jpg

[EarthKmTech]

On some machines there is a fusing mains power momentary switch for the right side door. Don't remember if there is one on the C360 series.

The entire rhs door is available as a spare part if it is damaged - if chassis is bent machine should be disposed of, end of story.

Mains power fluctuations can cause fuser errors on this model - particularly if a momentary large inductive load is sharing the same power circuit / outlet / powerstrip. Such as a refrigerator, large AC motor paper shredder, or anything else with a large AC motor for that matter.

Additionally, the fuser may look good but still be faulty. If all above checks out ok and the machine is a repeat offender I replace the fusing unit and it usually never comes back in.

[John Kaufmann]

The operation of the right door has a role in actuatate the fusing lamp power after is closed. ... After inspect parts manual i think that sw is the number 5 in attach.
switch.jpg

Thanks, that makes sense. I really appreciate you taking the trouble to post that picture and point me to that switch.

[John Kaufmann]

On some machines there is a fusing mains power momentary switch for the right side door. Don't remember if there is one on the C360 series.

Thanks. That's consistent with what Blizzoo wrote.

The entire rhs door is available as a spare part if it is damaged

Nothing damaged about the door. Tried a replacement IAC, but no change in fit.

- if chassis is bent machine should be disposed of, end of story.

Do you see that often? Any idea how the chassis gets bent? I think this is related, because the jam history has a lot of duplex transport errors, also suggesting door out of adjustment. From the history, that has apparently been going on for over a year before throwing the fuser error.

Mains power fluctuations can cause fuser errors on this model - particularly if a momentary large inductive load is sharing the same power circuit / outlet / powerstrip. Such as a refrigerator, large AC motor paper shredder, or anything else with a large AC motor for that matter.

Thanks for the suggestion, but this machine has its own office circuit, and still has an expensive surge suppressor. I think I can rule out power fluctuations.

Additionally, the fuser may look good but still be faulty. If all above checks out ok and the machine is a repeat offender I replace the fusing unit and it usually never comes back in.

Ah, but that's not when the chassis shows some sign of being bent? [Still trying to figure out how that happened, or how long it may have worked in that condition.]

[copier tech]

If this is a recent install the frame gets bent when the delivery guys use ratchet straps the secure the machine in transit & they pull the strap too tight, this can crush the frame etc seen it a few times

[John Kaufmann]

If this is a recent install the frame gets bent when the delivery guys use ratchet straps the secure the machine in transit & they pull the strap too tight, this can crush the frame etc seen it a few times

Iinteresting. It is not a recent install (been there almost three years), but the jam history indicates that problems with the door (and so, perhaps, the frame) go back a long way, perhaps to the installation. Can handling within the office aggravate that kind of problem, to the point of throwing the fuser temperature error? The machine should not bend when moved, should it?

[John Kaufmann]

On some machines there is a fusing mains power momentary switch for the right side door. ...

The operation of the right door has a role in actuatate the fusing lamp power after is closed.Usualy a door that is not fully closed or not actuatate that switch will throw warm up failure not abnormal high temperature.

After inspect parts manual i think that sw is the number 5 in attach.
switch.jpg

Interesting: I'm sorry it took me a couple days of thinking about it to recognize this question, but isn't that switch the one that provides the general 'right door not closed' warning, as opposed to a specific cut-off of fuser power? (The switch wiring goes to the PRCB (Printer Control Board) as opposed to the DCPU (DC Power Supply) that supplies the fuser power.) That general 'door not closed' signal may also be relayed from the PRCB to DCPU to cut off fuser power -- it would make sense, and there is a lot of communication between PRCB and DCPU -- but why wouldn't the error then be simply 'right door not closed', as opposed to 'fuser over-temperature'?