·
AHome
·
Blog
·
Electronics
Repair Questions & Answers
Two
Shorted Diodes But Four Replaced
A super market owner across the street came running to my shop and asked for a 1.5 amp fuse. He explained that the electronic scale that they have at the shop went dead. He said he will replace the fuse and let me know. Soon enough I found out that the fuse he installed gone open again which confirms my fear that the power supply in that device was shorted and needed repair.
The scale is too big to fit in one shot so this is the display of the scale and the next photo is the rest of the
scale.
It was not the best
clean electronic scale that I ever worked on; it was dirty and needed a lot of
cleaning. The repair is my job and the cleaning is the owner part.
So let us repair the power supply inside this device
It is a 24 volt power supply with 3 amps rating. I was not thinking of repairing it when I first opened the power supply. I thought of ordering a new power supply. The owner did not want to wait for the new part to come so he told me to go ahead and get it fixed.
If you look closely to the fuse, you would see or think it was intact but in fact when testing with the multi meter, the fuse was open. Since the fuse was open, the logic and common sense is to check first of all the bridge rectifier.
As expected, one of the
diodes was reading a dead short and the other diode was giving me reading both
ways. Four of the diodes of the bridge rectifier were replaced.
I saw this burnt mark
on the metal holding the power supply board but discovered later on after
testing the Mosfet that this burnt mark was old and other technician replaced
the shorted Mosfet with a new one.
After checking all the
parts on that power supply board, I determined to use the light bulb trick to
find out if there is still shorted part that I may have missed while testing
It was confirmed that
the power supply board is free of any shorted component and this is the time to
put the fuse back and get the machine working again
No comments:
Post a Comment