Peculiar problem with LG Flatron 21inch CRT Color TV

lg flatron tv crt

I am facing a problem with one LG 21" Flatron CRT CTV. Whenever I do a cold power-up of this TV, the mains circuit breaker on the main power distribution box trips. The circuit breaker is rated at 6 amps. This doesn't happen very often. If I leave the TV switched off for about 3 hours or so and power it on again, the MCB trips. Otherwise, all other TV funtions work perfectly.

I tried changing the circuit breaker. I even tried using a 15A rated mcb in place of 6A. Still it trips!

LG support has not been very helpful.Any help in diagnosing this problem is highly appreciated.

The model number is RA-21FE46VE. Do any of you have a soft copy of the service manual for this model that you can share? Thank you.

- Pooja

lg flatron tv user manual

If I had to guess, I would suspect the degaussing circuit. The degaussing coil is connected in series with a PTC resistor. This PTC resistor gets hot and quickly limits to current through the degaussing coil. Degaussing only occurs on cold starts.
My guess is that the degaussing coil has a short in it. The coil draws way too much current and trips the breaker. However, before the breaker tripped you built up some heat in the PTC. Therefore, if you reset the breaker and then repower the set, it may turn on.
Unplug the degaussing coil and see if the problem goes away. If it does, then you know the problem is in the coil circuit. (The degaussing coil demagnetizes the CRT. It usually has a two pin plug attached to the power board. The coil itself is clipped around the edge of the CRT.)

lg 21inch color tv repair

Banjo,

Thanks for the response. I checked the degaussing circuit. I unplugged the coil connector from the PCB and tried powering on. But the same problem persists.

Any one knows if the service manual for this set is available anywhere? The chassis is M- 091D FIGHTER.

LG Flatron 21inch CRT.

ptc tv crt

Hai PoojaK
I think the sugessions given by Banjo should work. Bocoz there is nothing except the SMPS and the degauss to trip your MCB. Ithink you should check all the varistors related to the power supply (MOV's) and the PTC which switches the degauss coil. As you have disconnected the coil and still have the problem, its very clear that the problem is with the above said components on the PCB. Best of luck.

Re: lg flatron tv crt

hi

just u replace the bridge rectifier diodes i think it solved

Not sure about the previous post...

Degauss is the obvious culprit but I have seen damaged thermistors in the degauss circuit before now. The thermistor module is actually two thermistors, one in series and one across the coil in most cases, it is possible for one to go faulty and still draw too much current even when the coil itself is disconnected.

Next question: are any other devices (VCR, DVD, Satellite etc) connected to the TV? A fault in the filter capacitors near the AC mains input can cause high leakage to chassis and create an unwanted current path via the attached equipment.

6A MCB is only just adequate for a TV with degauss and an SMPS. If you can, try a type B or type C MCB which have slower reaction times to overload.

Brian.