21 Inch Hotpoint CRT Television Dead Now Repaired
I received this television from a customer and the complaint was dead but Power On led is lit and red in colour. This means the television is getting power on the secondary side and also the microprocessor is powered but getting “all is not well” feedback and hence going into standby mode.
I hit the menu button and the television fired and I was able to see a faint line across the screen before the television went into standby again.
With this I got a clue that the problem is on the vertical circuit, therefore I can now open the set and do further testing on the vertical circuit.
I opened the set and before removing the board (Hv cap) I had to make sure there is no high voltage charge still held on the anode cap and this I did using the trick above.
I scanned around the vertical circuit looking for any suspects and was not able to pick any suspicious looking component.
So I decided to start checking all the capacitors around the circuit and I was able to pick one capacitor C451 (100uF/35V) whose ESR was very high as you can below.
I thought to myself that it is only culprit and therefore replaced it and again applied power and to my surprise the problem remained the same, no improvement at all. I pulled my meter and tested all voltages to the vertical i.c and I noted all pins had over 30 dc volts except the ground.
This is strange and I suspected the vertical i.c must be having a problem and therefore I replaced it too. I applied the power once again and this time the television came up beautifully but again I was not happy with the final product.
The screen had huge coloured spots as you can see below.
I suspected the posistor and therefore decided to check if it is okay or not. The best test for posistor is by direct replacement whenever you see colour patches on the screen. Usually if a posistor shorts it will blow the fuse and in my cause the fuse was intact and therefore suspected it was open.
When the posistor is open the television will still work but you lose the cleaning function of the degaussing coil which works together with the posistor.
Usually when the posistor is working it gets very hot and in this case I touched the top of the posistor and it was cold and with that I concluded it is open since like I said earlier a shorted posistor will always blow the fuse.
I replaced it with one I found in the junk board and after powering on the screen now crystal clear.
Thank you friends.
Humphrey Kimathi is from Nairobi Kenya and the author of
3) CRT Television repair course and
4) Basic Electronics course.
He is also a blogger at Electronicsrepairmadeasy.com
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