Sony KDL-22BX200 - no inverter

[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

[ocf]

Any idea if the computer CCFL inverter will be powerful enough to test the lamps in the tv? CFL tubes that are usually connected to this inverter are 12" coloured ones. Input to inverter is 12v

[ocf]

Update and some progress finally!

I received a generic LCD inverter model number AVT4029, I have included an image below, it takes 10-30v DC input and powers 4 lamps up to 22"



I decided to test this on a Bush tv that has an backlight issue, the input for the original inverter in the TV is identical to the above generic one. Both use a 6 pin connector, 2 pins each for ground and 12v and one pin each for Von/off and brightness adjustment.

The generic inverter powered the Lamps perfectly and the TV looks good!

Next step was to test the Sony with the inverter, unfortunately it does not have a 6 pin output as the bush did, in this case the inverter is combined on to the main power PCB.

I jury rigged the inverter to use the 6pin power from the bush tv and connected the lamps from the Sony. THEY ALL WORK!! The Sony turns on and picture is clear as day with the generic inverter so no lamp issue there.

Problem must be with the power circuitry of the inverter on the mainboard I am still only seeing 6v on the primary coils of the inverter this clearly should be 12v. I replaced the only capacitor that was on the inverter side of the power board but this made no difference. What could be making that 12v signal drop by half? When I put my multimeter probes on the primary side I see an initial 6v when the TV starts but this steadily drops and does not rise again as if a cap is is discharging.

The V on/off pin on the inverter connector that tells the inverter to turn on and off, does anyone know how this is triggered? I am thinking to jury rig the generic inverter inside the TV and hook it up to a 12V source on the power PCB but the inverter wont turn on unless it sees that V ON signal.

Any advice welcome guys!

[Turnip]

Hi ocf,

Had the issue maybe twice, both times transformer with shorted turns. My first one had a bulgy supply cap C2006(1000/16) so replaced it and noted the inverter supply voltage was 14v rather than your 6v and with a duff transformer.

Was initially confused as checked tranny secondary windings with an Avo and couldn't notice any difference - With a digital meter it was obvious - Chris.

[ocf]

Are you referring to the inverter transformer or the transformer that takes the AC input from wall and makes the DC for all the boards?

I have already replaced the inverter transformer and this has made no difference, also replaced all caps except 2 680uf ones that I didn't replacements for. C2006 has been replaced

[ocf]

I can get the generic inverter to power the sony's lamps if I give it 5v on the V on/off pin. I tested it with an external 12v and 5v transformer. If I could internalise this generic inverter and find a place to draw 12 and 5v on the mainboard then this could work.

I have found a 12v and 5v source but they are still live when power is off and the inverter needs to power down when the TV is turned off.

Any suggestions?

[ocf]

another crazy idea  -

Internalise both 5v and 12v power supplies, hook them up to the AC input internally and connect them to a rocker switch to be able to turn them on and off at will?

A bit extreme?

What else could be causing the 6v on the primary of the inverter coil. I can see a full 12v on D2031 and at various other locations on the board, could I just jump another internal 12v rail to the primary coil and cut the current lines to it?

[downunder]

Another thought, seeing that the Sony is "operational": Check the self-diagnostic service menu. May tell you what section has failed.
From standby, press display, 5, vol down, power on the remote. The display could give you a clue.         Bruce

[ocf]

I will try this today.

Any pointers on what I could test next, what would be the component that feeds the primary coils?

[ocf]

does anyone know if there are schematics for the board, I have the relevant sony service manual but it has nothing past a basic block diagram of the system.

[ocf]

I found a 5v rail that drops to 0v when tv is on standby jumpered this to V on/off of generic inverter and jumpered 12v + ground to inverter also. New inverter now turns on and off with the TV itself.

New inverter fits at a bit of a squeeze under the DVD player, its got a plastic cover and the underside of the DVD drive is thick plastic so I'm not too worried about arcing.

TV is reassembled for the most part and I am testing for the next few hours.

Looks like this one is fixed, unconventional repair I admit but it works! I wonder if the inverter will be ok with having a constant 12v source to it despite it not being used, hopefully without the 5v Von signal the 12v will just hang about untill needed and not stress the circuit somehow.