Electrolux ERG22 vacuum cleaner pcb fault

[momaka]

Re: Electrolux ERG22 vacuum cleaner pcb fault

I don't have the most experience with FETs but seems to me that I need to test the FET out of circuit and work my way back to the power switch if it tests bad.

Does that sound about right?

Not only that, but you CANNOT test components in circuit using resistance test or diode check or continuity when there is voltage in the circuit or a battery connected. ALWAYS remove all power sources when trying to test a component in circuit. Otherwise, you risk doing more damage to the board and also your multimeter (especially the case with circuits with higher voltages.) Also, those component testers are often inaccurate for in-circuit readings, so I don't recommend you use it for that.

So to be sure about the MOSFET... yes, remove it out of the circuit and test it.
If it's an N-ch FET, you should get a diode reading (~500-700 mV range) between Drain and Source when red multimeter probe is on Source pin. Reversing the probes should give no reading (open circuit.) Next, connect black MM probe to Source and touch the Gate pin with the red probe while using diode test. Then move the red probe to Drain. The MOSFET should now be turned on and you should see a low or almost no voltage drop between Drain and Source (as if the pins are shorted together.) If you touch the Gate pin with your finger, that should discharge it and the Drain-Source connection should disappear back into an open-circuit. Note that this test only works for testing MOSFETs out of circuit.
For P-ch MOSFETs, these tests above are the same, but just switch the positions of the red and black probe for each test... or use your component tester, if you prefer.

[Crystaleyes]

So, I have this Electrolux vacuum which had the batteries revently replaced and now it won't work.

The voltage from the batteries is arriving to the board without problem (+/- 12v) @ CN4 & CN6.
The motor works fine when voltage is applied to FM+1 & FM-1. The switching on and off is made in the negative line between CN6 and FM-1, and all components have been tested as fine apart from a FET.

The problem appears to be that the PHD71NQ FET (Q18) isn't switching when the power button is pressed.

I say this as when I started to connect my component tester to this FET, the motor fired up.

The exact situation was that one clip was on the Gate, and when the second pin was touched to the Drain, then the motor kicked in, nothing was connected to the Source.

Should also mention that there is the 12v on both the Gate and Source pins at all times. Drain connects via a couple of inductors (L5 & L6) to the motor supply.

I don't have the most experience with FETs but seems to me that I need to test the FET out of circuit and work my way back to the power switch if it tests bad.

Does that sound about right?