SONY LCD TV problem kdl-22BX200

If you shine a bright torch on the screen from various angles can you see any semblance of a picture? i.e. is it just the lack of backlight causing lack of visible picture?

In general Sony TV manuals are at Sony support.

Thanks Andy,

Yes I can see a faint picture. So I guess it is a backlight problem?

So if the tubes strike but draw too much current they would behave like this?

Bob

I should have been clearer, I need a service manual. I have found one paid for service manual which I ordered but the seller informed me that it had no circuits so I've cancelled that one.

Bob

I don't know. There are replacement CCFL and/or inverter kits available (ebay etc) for laptop sized screens, not sure if they're easily available for TVs ...

That's certainly the case on inverters for cold cathode backlight lamps on monitors, the they monitor the tube current and if the lamp doesn't strike within 2s or so then they shut the inverter down to avoid damage (to both). During the strike phase they output voltages in the 1kV or so range which folds back to a lower level when running.

A monitor that I had used 4 tubes, 2 top, 2 bottom with 4 separate feeds to the lamps split off 2 transformers, drivers and a dual channel controller chip. The chip controlled the shut down and if a single tube failed to strike then all lamps where turned off.

If you don't mind dismantling the screen to get direct sight on the tubes then you can usually spot what is going on. Replacement lamps can be obtained at reasonable cost but if one set stays off altogether then it might be an inverter problem and they aren't so cheap. Pink or obviously dim tubes are on the way out. Alternatively, connecting just one tube at a time to the inverter would give you a chance to look at each tube in isolation to see if one is out completely or dim during the

In the end, mine was an inverter fault following a tube failure (common) so I disabled one side of the controller (surface mount bodgery) and ran the 2 good tubes (1 top, 1 bottom) off the other inverter channel.

Can't see any on ebay at the moment. Still not sure if is the tubes - not all would fail at once or if the PSU is knackered or what.

Seems a shame to toss it away but possible not worth spending much money or time on it.

Bob

You could always send Sony UK support an e-mail. When I had one of their better cassette recorders, I found them very helpful until the spares stock ran out about 15 years after they stopped making them. As were my local Sony approved repairers.

Last time I used them they new how to charge for spares. Made Philips seem reasonable.

I've not got to the taking it apart stage yet - I did that with a laptop once to change the tube - horrible job - everything is so flimsy once apart! Pulling off the 4 inverter connections in turn has not given any clues as the unplugged ones over-volt immediately. I might try loading them with a resistor but the circuit might be looking for the non linear resistance curve of a tube if it is really clever. Not sure what the power for each tube would be - got to be a few watts and a few hundred volts once struck. So maybe 40kohms ish?? Total power consumption is 43watts according to the label so maybe half that for the screen? Maybe I'll have a play when I've more time. I only got the TV off freecycle last night as a "spares or repair" so it might go back that way.

Bob

In article , Bob Minchin writes

The tubes I've looked at were 5mA or so and I am guessing they will have a run voltage of 600V (quick look, maybe check data) which suggests a resistance of 120k but at 3W so better use a chain of resistors to survive volts and power. No need to go daft though if it's only on for a second or 2.

Insulate and keep the hands well clear though.

True recycling/DIY, good luck!

That TV seems to have an AZ1K-5-3 chassis. I can't find anything much on that variant either, I wonder how many basic design features it shares with the more common AZ1K chassis? Although that is a big screen chassis so the actual inverters are probably very different.

As usual I'd esr the caps before condemning the inverters, although the inverters do seem to fail on Sony sets...

After some searching I found a manual for the later KDL-22BX300 which uses the AZ1-FK chassis, it may have enough common features to be useful.Plus it's the same size screen so may use similar inverters:

Thank you very much for taking the trouble to post a link to that manual. The model is different and the inverter is different but it does give me some ideas for the sort of circuitry they use. I've also used the site to get a manual for our main Bravia TV No problems with that yet but good insurance to have the manual just in case.

Much appreciated

Bob

No probs :) I still reckon it's caps though! :)

Lee

Which caps are you thinking of Lee? The main PSU is fine. The inverter in your service sheet only has small value caps in the inverter and the tubes are run on AC.

Cheers

Bob

Sorry if you already know all this, but low esr caps in the PSU are a common cause of backlight/inverter failure. Even if the rails appear to measure correctly. I take it you've 'scoped the PSU rails to check for noise?

Lee

Doh! while I did mean *the* low esr caps give trouble I *meant* to say by drifting high esr. But you all knew what I meant ;)

Lee

Let me know if/how you fixed this because I have the self same problem. TV has barely been used