Mulja tv repair portal
Equipment Repairs => LCD TV forum => Topic started by: paul150470 on December 29, 2011,05:12:19
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:sign0144:
Hello guys, had a fuse pop in daughters bedroom tv, typical electronics smoke ozone / smellfrom back of case. Replaced fuse and popped immediately.
Upon opening the back up, a capacitor CX2 adjacent to coil LF2 shows a black line down its centre. This corresponds with the central moulding of the coil.
Capacitor appears OK, and is measuring 265nF, a little lower than its marked 33k, but it is showing a reading.
Coil is showing 8k-10kohms across any two terminals, excepting one pair which are showing 0.5ohms.
I'm guessing the coil is the problem! Anyone confirm this? What should impedance be?
I do have access to enamelled copper wire due to my work in electric motors, so could probably rewind the coil if I had to.
Can the coil be purchased from anywhere? would anyone have wound one before and have general winding instructions?
thanks for any info, Paul
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Hello Paul, You sound slightly teccie so you will be fine with this, the coil is effectively two windings on one bobbin, these are both isolated from each other no resistance should be measured. What spacing are the pins from each other?
Tony Walker
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As Tony says, there are two coils on that bobbin. It's even printed on the board which pins the two windings connect to.
Measuring between the two pairs of coil pins, you should get an ohmic reading, which will be the same for each winding. Testing between the two windings should give open circuit.
Unless there's a very low reading between the two coils, I am doubting this will be the reason for the fuse blowing. Look at the semiconductors. Starting with the mains input bridge rectifier. I suspect it's much more likely either the input bridge or the main chopper has failed, or even the PFC circuit chopper, but looking at it, I don't think there's any PFC.
The bridge rectifier is the rectangle between the big round black capacitor and the square yellow one, and the chopper will be on the heatsink to the left of that.
Post the part number of the board and tv model, that's a combined PSU and inverter on one board.
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Hi Tony, Dave;
yes, slightly teccie! But electric motors are my thing, I've wound a few prototypes in my time!
I agree, the choke certainly looks like two distinct coils and windings appear similar.
Coil A on left of the device measures 8.5 kilo ohms, Coil B on right side of device is measuring only 0.5 ohms.
I can also get a reading of 8 kilo ohms between the two coil ends.
They are wound with 0.4mm wire so I wouldn't expect the impedance to be too high really, but it looks like there is a connection across the two coils.
Looking at pin out of the choke, the 4 pins are on a 12.7 x 10.5mm square.
I can't see any physical damage on the choke, but the capacitor also pictured is immediately adjacent the choke, and the black 'smoke' line corresponds to the area between the two coils.
PSU board number is LS1904006A. I can take the bridge rectifier out next if thats next suspicios item. Certainly there's no sign of bulging or smoke damage to any components.
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both windings should read the same if you have some spare psu you
should get one to fit and cure fault
dave
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thanks for responses so far.
I will rewind the coils when back at work next week, and refit to PSU board before reassembling the TV.
Will report back results here