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Sony KDL-22BX200 - no inverter

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ocf:
Hi Guys,

I have a Sony KDL-22BX200, backlight comes on for a second then goes out. Known issue with this board. I decided to replace the transformer as the secondary windings were showing unequal resistance values, this did not solve the issue.

I really jumped the gun replacing the transformer as I can now see that input on primary windings is only 6v.

I have a bulb tester on the way that I will use to test the lamps. Should I test the inverter output using a fluorescent bulb?

Cant seem to find a schematic for the PCB and the Sony service manual doesn't have any detailed schematics for the power board.

What do I test next? I'm quite new to tracing circuits and understanding how they work any help would be greatly appreciated

ocf:
I just found the following thread - https://groups.google.com/forum/#!topic/uk.d-i-y/Gh4aFc-Q4SA

Same issue with same Sony model is being talked about , someone mentioned that a bad bulb could be the issue, inverter might be shutting down due to high power draw.

I have a universal inverter on the way but its not here till monday, I have an inverter from a PC 12" CCFL tube, would that be powerful enough to test the bulbs in the tv?

ocf:
Below is a link to a very high resolution image of the board, hover over the picture to zoom in on a section.

https://spares2repair.co.uk/sony-kdl-22bx200-power-inverter-vya194g-05-v-0

Tomorrow I will test the bulbs by connecting them one by one to the inverter to see if there's one that is causing the inverter to shutdown,
Any suggestions what I should test next other than the CCFL tubes themselves?

downunder:

Hi ocf,

Almost certainly you have a bad CCFL. Protection is so designed that any imbalance in the CCFLs will close the set down. For this reason you cannot
test 1 CCFL at a time. Protection will be triggered.

Best option is to strip the panel to expose the CCFL cavity so you can see exactly which lamp or lamps are inert for the short time you have when you
power the tv on. Even a lamp which glows pink rather than white is enough to make the tv go into protect.

You need to remove the lcd display (not needed for this test) and the various diffuser sheets...don't get these sheets out of order or back-to-front, or you'll be in all kinds of shite

Bruce

ocf:
Hi downunder,

Thanks for the reply! makes sense now that it could be one of the bulbs. That still doesnt explain the 6v on the primary windings, is this possibly a low power state the supply to the inverter goes down to when it shuts down for safety? Surely it would go to 0 and not just half the 12v input.

I will look over the schematic and get the CFL's uncovered ASAP

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