Broken Printer - What to check?

[Matsubaa]

My printer quit at the very beginning of a print. I left the room with it warmed up and homing. When I came back, I found it cooling and powered down with only a skirt printed.

I shut it down to reset and now only the power indicator on the motherboard turns on. I have no fans, no display and no indication of a connection on the PC end of the USB.

The PSU is delivering enough power to light the LEDs (which isn't much, granted) so I assume for now that it's okay.

What's my most likely suspect? Am I checking fuses? Replacing the motherboard? How do I narrow this down?

[wotor]

Check fuses first, if they blown out you have shortage in the system. Most likely heating element, temperature sensor or heated bed.

[William]

Hi，You can check if there are three lights on the motherboard when the printer is turned on normally.
You can refer to this:

v3板正常情况.jpg (221.89 KiB) Viewed 8051 times

I hope this can help you.

[Matsubaa]

I haven't gotten a chance to go back and open up the case to check which lights specifically are on but I did get my multimeter on the heater cartridge and I have ~11 Ohm. Casual Googling suggests this should be 14+/- 10% so this seems low. Did I find my short or is that not low enough to be conclusive?

[Matsubaa]

I've dug in and I have only the light labeled "12VB" (hard to read the silkscreen) lit up. Hopefully that narrows down the candidates for the short?

Honestly as I got in there, I see that the 15A fuse wasn't seated properly and the 10A fuse appears to have some kind of scorching on it.I'll clearly be dusting it out and replacing some fuses at the very least.

Update - Pulled out the connector for the heated bed and I'm reading 0.2 Ohm resistance across VIN to GND so I'm gonna guess I found the problem.

[William]

Hi, If there is only one light on the motherboard and there is a problem with the motherboard, you will need to replace it.

[Matsubaa]

Aside from the fuses, I don't know that anything's wrong.

Does anyone know the significance of the 3 lights? I assume they all mean something different and wonderfully diagnostic but I found no documentation what they actually mean.

[William]

Aside from the fuses, I don't know that anything's wrong.

Does anyone know the significance of the 3 lights? I assume they all mean something different and wonderfully diagnostic but I found no documentation what they actually mean.

Hi, If the three lights on your motherboard are not lit,
the printer will not work properly.

In the case of the VB reaction hot bed,
the VE feedback is the hot end and other cases,
and the 5V lamp feeds back the case of the LCD lamp.

[Matsubaa]

So for clarity's sake -

The 3 lights should be on, regardless of the condition of the fuses in question.
I've blown 1 fuse (10A) pertinent to the heated bed which my 0.2 Ohm multimeter measurement says is definitely shorted.

Am I definitely going to need to replace both the mainboard entirely and the heated bed?
Or am I definitely replacing the shorted-out bed and conditionally replacing the mainboard pending the fuse replacement?

[wotor]

If fuse is blown out, most likely your mainboard survived. Check if bed clips are causing the short, it is well known problem with them.