EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: ornea on February 03, 2021, 04:04:46 am
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Davo the robot vacuum sucked up some bathroom floor water.
Initial measurements indicated close to short circuit on the +/- input to the motor (VCM-200CLDA).
Found 2 mosfets shorted so replaced. It ran for about 2 meters then a puff of smoke and stopped.
Found additional failed mosfets so I have replaced all 6. (3 x N-ch 3 x P-Ch)
Before pressing back into service I scoped the gates of the mosfets but they are not what I expected. See attached.
Does this look normal. I was expecting something else. I have a 15ohm resistor in series with the 21.6v feed to limit current and limit damage. From the trace it appears it peaks around 300mA, I was expecting more. The resistor does get warm. (Very hot before I replaced the mosfets)
Happy to provide any additional info or pics. I am guessing what info to provide. I am hoping to make sure all is ok before I remove the limiting resistor.
There are 6 wires in the cable harness. I am assuming 2 for power and the remaining 4 are status and control signals. Can I assume that the mosfet drive sequencing is generated on the motor PCB and not from the main controller board. Is that typical?
The pink trace is the volts across that resistor, the other traces are connected to the gates of the three N-CH mosfets.
Warmly welcome and suggestions, tricks and advice.
[attachimg=1]
Image showing the hookup
[attachimg=2]
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Have attached the Gate traces to the P-Ch mosfets in the hope it may prove useful.
[attachimg=1]