1st Gen M2 heat bed dead again :(

[javafuel]

It died during a 16 hours PETG print job with 90C heat bed. Based on the look of the print, it stopped heating early stage of the print job. This is the 3rd time it has stopped working on me. Previous two incidents were involving printing ABS and power connector melted.

I've added a big MOSFET after the last incident. There is no melting connector this time, and heat bed LED indictors (on viki LCD and MOSFET) turn on when heating command is sent (via Proterface USB and SD). The original 12v PSU brick's LED is on as well, but the bed just doesn't heat up at all.

I'm clueless as what went wrong this time. Any suggestions would be appreciated.

[ednisley]

original 12v PSU brick's LED is on as well

The fundamental problem is the absurdly high current drawn by the 12 V platform heater.

All those LEDs show the low-current control path works fine, but I'm reasonably sure the teeny LED on the front of the platform isn't glowing, so the high-current path is broken.

The platform heater connector sits at an abrupt angle to the back of the platform, so I suspect it's flexed often enough to break a joint inside the heater. Some folks have repaired that connection, but I'd treat it as a message to upgrade the platform to a +24 V heater. Install the new platform, keep the external MOSFET, swap in a 24 V supply, and you're good to go.

It could be a failed wire between the MOSFET and the platform connector. Even if it's the heater, those wires are due for replacement with heavier-gauge silicone-insulated wires, because the original PVC insulation gets crumbly after a while.

A multimeter will be your friend: a big voltage drop anywhere other than across the heater locates the failure.

[javafuel]

original 12v PSU brick's LED is on as well

All those LEDs show the low-current control path works fine, but I'm reasonably sure the teeny LED on the front of the platform isn't glowing, so the high-current path is broken.

That little green LED is on while heat bed command is sent.

but I'd treat it as a message to upgrade the platform to a +24 V heater. Install the new platform, keep the external MOSFET, swap in a 24 V supply, and you're good to go.

It's on the bottom of my to do list because it requires so much time to rewires everything, plus replace all 12v parts that I've already invested in.

Thanks for the advice, Ed. I'll find time to troubleshoot it. Wish me luck.

[ednisley]

That little green LED is on

Mmmmm, my remembery has failed.

I thought there was an LED on the edge of the platform, connected in parallel with the heater power. That's not what you have, alas.

Turn the power off, unplug the heater connector at the platform, and measure the heater resistance. If it's more than a few ohms, there's your problem.