MOSFET Question / All things Extruder dead

Kind of a newbie here, but I think I might’ve fried my MOSFETs. my XY&Z steppers all work fine, but the first attempt at a print started off ok, the hotend began heating, but the fan wasn’t running. I assumed it wouldn’t start until it reached a certain temp, but then the hotend temp suddenly started dropping… all the way back to 22 degrees (room temp). THEN the fans kicked on. Now neither works. XY&Z all still operate fine though.

I purchased everything from here with the 30a upgrade a few weeks ago.

I checked voltage and with the ground on the 4 pin power plug I’m getting 12v at D8+ D9+ & D10+, but with the positive on the power plug I’m not getting any appreciable voltage from D8- D9- or D10-.

The thermister seems to be working fine, it warms up from body temp and seems to read fairly accurate.

a visual on the MOSFET & Poly fuses shows no signs of overheating or damage and all solders look fine.

I never even hooked up the bed, so I’m not sure how I could’ve fried that one too… is there something else I should be checking?

I may have found the problem… I checked resistance to the hotend heater and got nothing… ZERO ohms… so that seems to indicate an open circuit… I pulled the heater element and applied 12v directly to it and nothing… so I’ll try to find another heater element and see if let y’all know if that fixes the problem.

I’m also getting 12v @ D9 & D10 now…

Zero ohms indicates a short, not an open. Check to see where the power wires are soldered to the plate in case you’re only dealing with a bad solder job.

You’re right, perhaps better stated “The needle never moved when connected”, so it’s an “open”.

I checked the wires going into the heater cartridge and they appear ok, but still no love… (or heat). I picked up a new one at the local electronics store, will give it a shot.

Thanks for the clarification, I’m an clearly not an electrical engineer. But I’m learning!!!