V2.1.4 Heated Bed FET problem?

[bmeehan19 0]

Hi,

Im new here, Ive tried to find a solution to what I think is an issue with my pcb. I think I may have caused the danage. I didnt have and equipment plugged into the board I just wanted to test it after receiving it. The only light on was green initially. I then turned it off and unplugged the psu. I inadvertantly turned it on without psu plugged in and the lights flashed quickly. I reconnected power and turned on again. I do hear the heated bed relay "click" and now the red indicator light associated with the heated bed receiving a signal to power on is lit up constantly. If I remove one of the safety jumpers it goes out. If i leave the safety jumper out and cycle power it stays out. If I replace jumper and cycle power it lights up again. Ive also tried recompiling firmware. Nothing shuts the light off. Is this a FET problem? Could I have damaged it with cycling power not hooked to psu?

Thank you,

Bryan

Edited June 2, 2017 by Guest

[bmeehan19 0]

Does this sound like a damaged FET? Any insight on the symptoms or what else it could be?

[fbrc8-erin 298]

I'm not really sure how you've got it set up, from your description. Could you provide photos?

Regarding the safety jumpers, the printer _will not_ power on correctly without the jumpers. On a UMO+ I think it looks like it powers on, but you can't move the extruder or heat anything.

On a UM2, you get an error message about the safety circuits.

I do not recommend attempting to power it on without the jumpers in place.

[Torgeir 264]

Hi bmeehan19,

What you assume here sounds quite right, -however, this approach should normally not destroy your PCB... So was this really what happen???

OK., anyway you should measure the input voltage to the FET, the voltage from PG5 into the resistor R54. This voltage should be at lo stage, less than 0.4 volt (approx). If this is true your FET Q1 needs to be replaced. You could also short the R57 right across the resistor -and NOT to any convenient ground point around -but across the resistor itself. If the light goes out, your processor is to be blamed -or changed...

When you indicate this is the problem, you sure have an electronics background...

So go on and do this test and please report back.

Thanks.

Torgeir.