My CR-10S printer has stopped working. The heated bed does not heat. I checked and I am not getting power to the bottom of the bed. The soldiered connections look good. I traced back to the mosfet board and discovered that two LEDs are lite up. When I measure the voltage on the mosfet board I have 12v between the red and the outside black wire, but no voltage between the red and middle black wire. Is the problem the mosfet board or the motherboard?
Without schematics it’s hard to know. You’re correct in checking the voltages. The n-channel mosfets are used as a low side switch, so the 12v will always be on. What you need to check is the voltage drop across the heated bed (measure the voltage from the 12v supply side of the bed to the other side of the bed) while its on. It should be close to 12v.
Then check the voltage from the gate-source on the mosfet. It should be 3.3-5v depending on the mcu voltage.
Finally you should disconnect the heated bed and measure the resistance between the two terminals of the bed heater, this should be pretty low.
Thank you for all the information. I have a new mosfet switch coming this Monday. I will try that first, since the mosfet switch does turn on intermittently and I get 10.5v at the terminals on the heat bed. When that happens the bed does heat.
The new MOSFET will not help you much, if you have nothing where you could connect it. The pins of the current MOSFET seem not the best choice. You would have to use a spare pin of your board and have to change the firmware so that it uses this pin.
Sorry for the confusion. I have a new mosfet board coming on Monday.
@Robert_Setterlund If this is an answer to my post, then it makes no difference. Normally you attach this new MOSFET to the connectors for the heatbed of your board, but you have problems with that, so it will not work.