3D Printing: Simply cannot get Monoprice Select V2 hotbed to heat up. I have redone all wires.

[suchamoneypit]

My hotbed simply won't heat up. It is upgraded with a Mosfet installed by someone else (bought secondhand). I opened up the box portion with the PSU and saw the power cable to the Mosfet from PSU had fallen out it was so loose. I rewired it with solder and though for sure that was the fix. Put it back together, no go. Bed doesn't raise in temp at all. I take it back apart and now an additional power cable and ground cable going to the mosfet had fallen out. At this point I think for sure this is the problem, and I take out, and properly solder all 4 of the main wires for the mosfet installed, and test all cables relate to the hotbed to make sure are all firmly installed and no looseness.

 

After this, turned on the printer, and it immediately heated like a champ to 70C, and started printing. 1.5 hours into its 5 hour print and the bed temp drops off again, eventually down to ambient. Now its back like it was, not heating up at all even after 25 min. I took it apart, rechecked every cable going to/from the mosfet, and they are all still good. Worth noting before it seemed to randomly work sometimes after sitting for a few days. Seemed to begin working again with no rhyme or reason.

 

Im very confused, printer has been down for almost 1.5 months because I've been busy with other things. Im not sure what some other failure point are.

[WereCatf]

If it's working sometimes and sometimes not, it's a loose wire/solder somewhere.

[suchamoneypit]

16 minutes ago, WereCatf said:

If it's working sometimes and sometimes not, it's a loose wire/solder somewhere.

I've triple checked all connections within the PSU box area. Maybe im gonna have to flip over the printer (annoying) and see if I can see anything physically under the bed. Not exactly sure what im looking for or if there is a connector that can come loose or something.

[suchamoneypit]

Someone has suggested it could be a faulty mainboard citing issues they had and fixed. I'm going to try and poke around with a multimeter to figure out if that's the case. Hopefully I can help someone else out with the same problem by solving it.