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Shorted board, no enable to heater or fan mosfets

Posted by mxaniac 
Shorted board, no enable to heater or fan mosfets
September 04, 2017 11:48AM
I have a Tevo Black Widow with a 24V RAMPS 1.4 board. I was plugging in to the USB port while the printer was on which is a bit of a convoluted path when something sparked and I smelled the uhh ohhh odor. I didn't see what I touched, the printer is on a cart with the controller box inside on a shelf and hard to reach so I didn't see much but a spark in the shadows. I believe the legal term for my action would be negligence (A failure to behave with the level of care that someone of ordinary prudence would have exercised under the same circumstances.), regardless it's done now.

I have no fan or heaters, everything else seems fine. LCD does seem pretty dim when running on USB power though. I can't see any burned traces, fuses seem to be fine. Everything has the +24V, and the mosfets work correctly but they are only getting about 1.6V on the enable pin when I turn on the heater. That trace runs to some 8 pin devices with labels like RPK1, they are labeled much like resistors with 100, 104, or 182 printed on them. I'm not an electronics technician nor a EE, I don't know what these devices are or how to test them. Since the problem exists on all 3 circuits it is probably not them though.

Vcc does test out to 5V if I use a GND pin on the same header as a pin labeled Vcc. If I do Vcc to input power ground it's less than 2V.

I haven't figured out the schematics I've found. I don't understand what P$1-P$6 are on the wiki schematic, although my board isn't exactly the same.

I'm hoping someone could steer me in the right direction on resolving this. Any help would be appreciated.

Thanks,

Rich
Re: Shorted board, no enable to heater or fan mosfets
September 04, 2017 01:23PM
This is the board I have: MKS 1.4

I put a jumper between the input GND and the GND on J2 (test header perhaps?) and now my heater works, but the servos just squeal when you turn them on. D3 now lights up as well.

I should probably just buy a new board, are any of the others like the MKS-Base 1.5 a worthwhile upgrade or should I ignore complications in my life and replace it with exactly what's in it now?
Re: Shorted board, no enable to heater or fan mosfets
September 05, 2017 01:48AM
The RPK devices are just 4 resistors in a convenient 8 pin package of the value stated (100, 104, or 182) (10 ohm, 100k ohm, 1.8k ohm)

From your description and tests, it seems like you have burned 1 or more tracks on the board.
Re: Shorted board, no enable to heater or fan mosfets
September 05, 2017 09:23PM
Ahhh, RPK - Resistor Package. Makes sense.

I ordered a new board, no reason to deal with the hassle and frustration of trying to repair the old one.

Thanks,

Rich
Re: Shorted board, no enable to heater or fan mosfets
September 08, 2017 02:18PM
Still have the same problem with the new board. I think I fried the 8825 drivers because most of them have no Vref and get extremely hot immediately.
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