Shorted FETs In Dental Device Repair
This device has visited my shop a while ago with water damage issue. Today the same machine has come back dead but not sure what the cause; let us find out.
When powering up the device there was no sign of life whatsoever and that was enough reason for me to open up the machine and check it out.
While the machine connected to power, I traced the 220 source to the main transformer and I was getting that.
I also checked the main AC power going out of the transformer and I was getting 10 AC volts to the red and black wires as you can see in the photo.
When I checked the power DC power going to the main capacitors I was getting nothing so the logical thing to trace backward to find the problem and sure enough I found it.
The fault was the two Mosfets that feed power to the main capacitors and when I checked the power there sure enough there was no voltage reading either. Part number: P40NF10L (I already shared the data sheet in the previous article).
Both were shorted out and needed replacement. I still have the same exact parts from the first repair that I did on this device.
I replaced the two shorted Mosfets, checked for any cold soldering but found none did some cleaning and I powered on. As it is seen in the photo, the device is up and running. The customer was happy to get his machine working again and I was too.
This article was prepared for you by Waleed Rishmawi, one of our ‘Master Authors’ and currently working in the Bethlehem area of Palestine repairing electrical and electronic equipment.
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Note: You can check his previous article on Shorted 2SK2837 FET In Welding Machine