I received a phone call from my neighbor to pass by his
place to check on his decoder which he believed was hit by power surge.
I passed by and the decoder was brought to me but since I
had no tools to open it up I decided to take it with me to my workshop.
Once on my workbench I opened it and I scanned the board
(power and main board) and I could not see any suspect component.
They all looked very innocent, I pulled my meter and tested
across the main fuse and found it open. Fuses rarely die of old age, there must
a reason why and in most cases they die when there is a short on the supply and
therefore I started testing components on the power supply which are directly
connected to the main power line.
So I decided to start with the rectifier diodes and I found
one which was shorted and this put a smile on my face, this must be an easy
fix!
With this I concluded there are still shorted component(s) I
did not pick, I continued checking and I could not get any other component and
this caused me some stress because I had marked this assignment as simple.
I removed the diodes one leg from the circuit one by one and
applying the power via the series bulb and once I removed the last diode I
noted the bulb was now dim (off) and I realized the diode was failing under
load since I was not able to pick it using the meter.
That is why when you find one diode is shorted, it is
advisable to replace the four diodes otherwise the chances of the customers
calling back with the same problem is high.
I replaced all the four diodes and after applying the power
via the series bulb, the bulb was bright and then dim and with this I concluded
no more shorted components in the supply.
I connected the power board back to the main board and the decoder
worked like a charm.
Thank you friends
See you in the next class
