E Studio 350 fuser heater question

[cooked]

There are two thermistors on the fuser. An edge thermistors and a centre thermistor. The error 9 indicates either of these has detected an over temperature. So it looks as you say to be the control of the IH (induction heating) coil. There is no control itself in the coil. The coil is connected directly to the IH board which is switched by the logic board. I would suspect the IH board is permanently on. It is less likely to be the logic board.

Just to add to confusion...

The heater element is not permanently on. It is only turned on when it is required. for example if the side door is open the heater is not on. It just seems that when it is on, it is not being regulated.

So the edge sensors are working. ( The machine is detecting over temp from them ) They must go to a board ( possibly the IH board ?) where they help with the heater regulation. It could be that there is a problem there. Where is the IH board located.?

Doug.

[Ropariva]

There are safety mechanisms in the Toshies that cut the 24v rail and therefore all high voltage including feed to the IH coil. Any of the doors opened will cut the power to the IH.
The IH board is directly behind the Fuser unit

If you can check that there is power permanently to the IH coil from turn on to machine fail, then I think your board is faulty.

[blackcat4866]

On these old beasts you can have the white sheath worn through, shorting the heater to the roller. If you find the short you need to change the heater and IH board together. =^..^=

[Ropariva]

That's absolutely correct. Seems the board and coil are ok in this one, just not switching off. If the coil had shorted there is usually obvious splatter marks and the board will also be dead.

[cooked]

Hi all, Update on problem.

I checked the IH board with Huntron and found nothing that would indicate a problem.

This turned my attention back to the sensors. I had previously eliminated them because the impedance dropped with heat which I was expecting. I spliced in some old sensors from a E 351C (and modified the mount to fit), The result was that the heater was being regulated, all be it at a temperature that was too low for proper fusing. This definitely eliminated the IH board and pointed the problem back to the sensors.

I have since ordered and received (took over 2 weeks to arrive in NZ) a set of sensors which has cured the problem.

It appears that the sensors must have gone slightly resistive. The resistance of the original sensors were about 800K when cold. The new sensors where just over 1 M ohms.

Thanks all for the help.

[buuluu]

Thanks,

I have done this a number of times after taking the fuser out and checking or rechecking. The result is always the same, machine goes through the motions of starting up then stops with the service spanner and error code C440. 08-400 shows 9.

Doug

Replace two thermistors. It will be Ok.