I got a phone call from a client who wanted his television checked by a technician, it was a referral case from another client I had repaired his gadget previously.
He directed me to his place within the neighborhood and was able to trace his place. After sanitizing my hands, I was ushered in and shown the television.
I asked for brief history and was told they shut it down previous evening and in the morning the television never wake up.
I applied the power to confirm what they said and indeed there was no sign of life even the standby light was absent.
With that I took the television to my workshop and after opening it I went straight to check the state of the safety components beginning with the main fuse and to my surprise noted it has a thick jumper wire across it and this lead me to conclude the television had a previous repair.
I soldered another jumper wire across and this time applied power using the series bulb current limiter and noted the bulb was very bright nonstop.
I did voltage testing across the main capacitor and got very low voltage and this confirmed to me that there is a shorted component before this capacitor or the capacitor itself is shorted.
Using digital meter set to diode mode I tested across each diode and the main capacitor and got no beep at all.
This lead me to conclude the component causing this problem maybe failing under load because the meter could not pick it up.
I decided to use my multi-component tester to test the four rectifier diode and these were the results.
According to the results I got I was not happy with diode 3 and 4. I changed the two diodes and again applied powers and still the bulb was very bright.
I then decided to check the status of the switching transistors and noted one was dead short.
Like I have said the television had a previous repair and seems the technician changed these two mosfet 6N80C which was previously smd mosfet 5n70D.
I decided to google the specs of the two transistors and realized the later was more powerful in terms of power handling.
I went to the shop to buy these components and realized in my market they never store smd components and that why the previous guy used this type (non smd) I decided to go his way and bought 5N60C, still not exact specification with the original but within.
After replacing those components including the main capacitor, I applied the power again using the series lamp current limiter and noted the bulb was dim, in fact almost off and with this I concluded no more shorted component and I can now safely replace the main fuse with a new one rated 3.15A.
I decided to re-assemble the motherboard and applied the power and noted the standby light is red, I pressed the standby key and noted the back-light are on.
I lifted the TV flame a bit since I had put it upside, screen lying on a soft material and could see “no signal” on the screen, I started to celebrate the success.
I decided to keep the TV on for 3 minutes and shut it down again and removed the power cable from the outlet and decided to touch the component I replaced and noted one of the transistors just replaced was getting very hot.
I figured that could be the problem why the transistor shorted in the first place, I decided to add a heat sink to this transistor as you can see above.
I took the TV back to the owner and informed him the component I have used which are not exact but promised to imports the exact soon and will do replacement immediately they land here in Kenya.
I asked the owner how they shut down the television at night and they told me by remote only and I advised them to be switching from the socket otherwise they will overwork the components.
This is the final results
By Humphrey Kimathi
Author LCD LED television repair guide