This machine has had C440's on and off for a year. They always reset, and don't blow the thermostat. It's had three or four sets of thermistors. Today I think I found a cause. It helped that it had a mild meltdown. The pressure roller stuck to the heat roller in the center then ripped free.
The new thermistors still look new. No surprise there. But when I pulled the side heat lamp I noticed burn marks that exactly coincide with the meltdown area on the heat roller. My theory is that this lamp had some particularly hot spots toward the center of the lamp, and when it heats the outer edges on longer runs, it's also blasting certain areas in the center of the heat roller with excessive heat.
eS305 C440_9 1.JPG
The fuser frame was busted out around the claws, so I brought with the frame, heat roller and lamps. I believe this next part is more consequence than cause. When I removed the metal frame within the plastic frame, I found the black wire to the thermistats was melted through it's insulation and the metal frame was probably hot (120vac hot, and 240C hot). I didn't have a nice convenient solution for that one.
eS305 C440_9 2.JPG
I still have some of those nice silicon thermistor tubes that protect the wiring to some thermistors. I cut one in half lengthwise and laid it between the wire and metal frame, then tightened down the screws. I'm sure that will be adequate to insulate it electrically from the frame at normal operating temperatures.
I'll be curious if the power issues make any difference (sags of 12vac hot to neutral, and spikes of 7.0vac ground to neutral). Maybe the power issues may change.
I haven't seen a heat lamp like that since the Canon NP-1010's and NP-1020's. Often the lamp would swell up or warp so much that you couldn't change the heat roller without busting the swollen lamp. =^..^=
The new thermistors still look new. No surprise there. But when I pulled the side heat lamp I noticed burn marks that exactly coincide with the meltdown area on the heat roller. My theory is that this lamp had some particularly hot spots toward the center of the lamp, and when it heats the outer edges on longer runs, it's also blasting certain areas in the center of the heat roller with excessive heat.
eS305 C440_9 1.JPG
The fuser frame was busted out around the claws, so I brought with the frame, heat roller and lamps. I believe this next part is more consequence than cause. When I removed the metal frame within the plastic frame, I found the black wire to the thermistats was melted through it's insulation and the metal frame was probably hot (120vac hot, and 240C hot). I didn't have a nice convenient solution for that one.
eS305 C440_9 2.JPG
I still have some of those nice silicon thermistor tubes that protect the wiring to some thermistors. I cut one in half lengthwise and laid it between the wire and metal frame, then tightened down the screws. I'm sure that will be adequate to insulate it electrically from the frame at normal operating temperatures.
I'll be curious if the power issues make any difference (sags of 12vac hot to neutral, and spikes of 7.0vac ground to neutral). Maybe the power issues may change.
I haven't seen a heat lamp like that since the Canon NP-1010's and NP-1020's. Often the lamp would swell up or warp so much that you couldn't change the heat roller without busting the swollen lamp. =^..^=