Power FET and 5 Watt 2.2 0hm Wire Wound Resistor Problem
The complaint by the customer for this 21″ CRT Philips TV was no power. No power problem can be due to the main fuse open circuit, bad On/off switch, bad power components, shorted components in the secondary side, dry joints and etc. No matter which component or circuit that can cause no power, one has to always check on the main fuse first.
When i measured the main fuse (as seen in the photo below), it was tested good. Even the On/off switch also tested good. If you are comfortable in checking the AC supply input, you may do so as different repairers will have different procedure in doing their troubleshooting job.
When i measured the main filter capacitor there was no voltage and this means there must be a component that had an open circuit preventing the current from reaching the main filter capacitor. So I began to check on the components after the main fuse and I found a 5 watt 2.2 Ohm resistor had an open circuit-see the photo below:
Usually there will be a reason why the resistor had open circuit. The reason is most probably there is a shorted component (semiconductor) in the power primary side that had consumed too much power causing the resistor to open. Just before I check on the power FET, I saw that this FET pins/legs had dry joints as seen in the below photo:
I took the power FET and check and it was indeed shorted. I continued to check on all the components in the primary side including the SMD components and all were found to be good.
Note: If you want to learn the fastest and accurate ways to test components, I can recommend you Jestine Yong’s ebook on Testing Components.
The shorted FET part number was FQPF7N60 and finding it from the local market was not that tough. As for the resistor, since I can’t find the 5 watt 2.2 Ohm resistor, I have used 7 watt 2.2 Ohm as replacement.
After fixing the components, I connected a 60 watt bulb in series with the ac supply to make sure that there is no longer short circuit.
Once I powered the TV (with the series light bulb trick) I could see that the bulb was not bright and it went to dim straight away. I could also see the standby LED was lit which indicates a good sign I can put in the main fuse and power the TV up.
Once I put back the main fuse and turned the TV ON, below picture was seen. I’m glad that the TV was fixed and managed to earn some income from this repair work. If you want to learn how to repair CRT TV then you can get Humphrey’s Ebook HERE.
This article was prepared for you by Suranga Bandara who owns an Electronics shop in Anuradapura, Sri Lanka.
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