Thermofuse Cross-section

[mojorolla]

Re: Thermofuse Cross-section

In the highly unlikely even that the worst should happen, and the connection NOT get broken when it should, I don't think I would want to be the tech responsible for that fix.

Some years back, we had a tech replace the 91 degree scanner lamp thermal fuse with a 192 degree one (from the fuser) on a Canon NP400 to get the customer running.

Whatever circuit it was that controlled the scan lamp stuck "on" after-hours that night.

The following morning, the customer was greeted by a blob of molten plastic parts, including the bulk of the doc feeder.

We had an emergency service meeting the following morning getting warned to NEVER EVER do that.

(No, the tech did not get fired, as he had a very good relationship with the customer, but almost anyone else probably would have.)

melted ADF.jpg.................................................. ....................doh.jpg

Anything can be taught, except common sense.

[Lagonda]

Re: Thermofuse Cross-section

Speak of the Devil........
Just as I post our techs are not allowed to bodgy thermoswitches look what turns up....

Thermofuse.jpg

If i work out who did this he's going to be explaining to his wife why they cant pay the mortgage at the end of the month.

[Shadow1]

Re: Thermofuse Cross-section

Now that's vastly different than resetting one. That is a safety hazard, although thankfully they didn't bypass both thermostats.

[DAG COPIERS & COMPUTERS]

Re: Thermofuse Cross-section

Hey KenB, go ahead & finish up the story. How did you eventually solve the customer's problem? Did you give her another machine?

NeoMatrix, If I were you I would start by replacing the faulty thermostat itself with a new working one and see what happens next, rather than replacing the entire fixing unit. This would definitely remove any iota of doubt on a possibility of any other faulty component within the fixing unit. Just as Blackcat has said, certain Transfer bushings INTENTIONALLY use conductive plastics.

There is also the possibility that, the real culprit or faulty component could have been the THERMISTOR, itself a TRANSDUCER , which was not regulating the temperature of the unit-(UHR), therefore sending faulty electrical signal to the DC controller. The reduced ohmmeter reading, with the thermostat in circuit, in parallel with other components should have prompted you to suspect & investigate other components in the circuitry esp. the thermistor.

Generally, Insulation breakdowns, be they Thermal or Electrical is a common phenomenon in Electrical circuits . It occurs when the stress (Heat or Current) acting on the component exceeds the Tolerance limits specified by the manufacturer.