Westinghouse SK-32H240S Continued problems

[retiredcaps]

Re: Westinghouse SK-32H240S Continued problems

as for the secondary windings:
i'm not sure which is primary and which is secondary when looking at them, but i measured the resistance of the transformers connections from top to bottom and this is what i got. (in circuit)
1. 1765, 1760
2. 1807, 1805 (the new replacement)
3. 1733, 1728

The readings above look good as per

http://www.lcdparts.net/TransformerD...ProductID=2774

Going from here will be more difficult since most of the easy things are already tested.

Basically the inverter PWM IC works as "all or nothing". Either all the ccfls and its circuitry works or nothing. The PWM IC will take 2 to 3 seconds to make that decision.

The main culprits are bad caps, bad ccfls, bad ccfl wiring and bad inverter transformer windings. From your tests, it seems the only left is the pwm IC and it circuitry which isn't easy.

[MajesticMike]

Re: Westinghouse SK-32H240S Continued problems

couldn't i some how override that decission to shut off the backlights and jump power somewhere to force the backlights on? or provide my own power from another source to turn on the existing transformers?

[retiredcaps]

Re: Westinghouse SK-32H240S Continued problems

couldn't i some how override that decission to shut off the backlights and jump power somewhere to force the backlights on?

I'm not the type of person to "over ride" any protection mechanism. For one, I don't want to be liable for any ramifications of such actions.

Others have done it using either/or

a) resistor
b) capacitor
c) shorting out pwm ic pins

[selldoor]

Re: Westinghouse SK-32H240S Continued problems

as for the secondary windings:
i'm not sure which is primary and which is secondary when looking at them, but i measured the resistance of the transformers connections from top to bottom and this is what i got. (in circuit)
1. 1765, 1760
2. 1807, 1805 (the new replacement)
3. 1733, 1728

Whilst the replacement may be in spec with what lcdparts suggest we usually look for each pair to be within 3% which they are but 1728 v1807 is more than 4% so that could be triggering the protection.

[kerbsjacob]

Re: Westinghouse SK-32H240S Continued problems

hello everyone, same symptome here. I have replaced a fried transformer to only get two seconds to black symptom. I have a fair amount of experience with lcd tv's, fixed many with many differnt problems.

This unit has darfon B070-401. I replaced a burnt transformer. Unit still went back into shutdown mode. Cause appears to be inverter chip LX1692. All ccfl are good. The ccfl chip has a pin that connects to cap and works as a timer to transistion between ignite and run mode. The chip has an internal current source to charge the 2uf cap. when voltage rises avove .5 v the overcurrent protection is enabled, when the voltage rises above 3.5 v the overvoltage fault is enabled. By bypassing the cap with a 1 meg ohm resistor I am able to prevent the voltage on the pin from rising over 2v, this prevents the overvoltage fault from being enabled. I do not know if the controller exits ignite mode or not. However, with this bypass resistor installed, the lamps will all stay lit. The odd thing is that the overvoltage input voltage does not appear to exceed the threshold at which the fault should be triggered.
Anyone have any suggestions, I cant tell why this thing keeps shutting down or why bypassing the timer cap to prevent over voltage fault will cause it to stay on. I think something besides overvoltage is also changed or disabled, but dont know what. Unfortunately it is not safe to leave the 1 meg resitor installed, as it wont shut down on open lamp or high voltage arc. this could cause a fire.

Does anyone have a schematic to show what is going on for the protection on this board. I looked at the datasheet for the lx1692, but it only has an example of the single transformer application. this unit uses three transformers, so there must be an op amp or other circuitry inbetween that converts the fault signals from all three transformers to the info that is used by the chip. The voltages that come from the high voltage feedback caps range between 24v to 30v peak to peak on a sinusoidal waveform. no caps are shorted and voltages appear to be fairly consistant.


I have a feeling that replacing the other two transformers may solve the issue as the old ones are not matched perfectly tot he new one. I really want to understand how the protection works and why this small difference triggers the fault protection. Really I cant be shure which fault mode is being triggered, or if the chip never enters run mode. From the datasheet of the driver, I cant seem to determine why the the thing shuts down.

Does anyone have a detailed schematic, this thing is driving me crazy!

[bpopilek]

Re: Westinghouse SK-32H240S Continued problems

Hello, I am too in possession of one of these wonderful TVs and have the same backlight issue. I have already replaced a defective transformer that was burnt very badly. In addition, I only showed one cap to be bubbled and defective, so it too was replaced. I am not still sitting here with the same 2sec to black problem. Outside of buying a replacement power supply board, can anyone help further?

kerbsjacob, can you tell me what pin you jumpered on the LX1692 so I can see if I have the same results? Thanks!

[kevinm34232]

Re: Westinghouse SK-32H240S Continued problems

I just picked up 18 of these models from a hotel, Im assuming all have the 2 secs to black problem. The one that I tested did. Im also assuming most will be bad transformers but Ill have plenty of working ones to test on if you guys need voltages to compare, etc.

[retiredcaps]

Re: Westinghouse SK-32H240S Continued problems

Im also assuming most will be bad transformers

ebay hint. Ask the seller who is selling just one 4301H if they will sell multiples at a discounted price. You would be surprised at the answer.

[kevinm34232]

Re: Westinghouse SK-32H240S Continued problems

One thing Ill mention is this TV shuts the backlight off in about 10 seconds when there is no input connected and that could throw you off if you don't know that

TV1 was fixed with replacement of T3 (open secondary winding), and replace C611 (470uF 25V), C710 (1000uF 10V) both bloated.
TV2: T3 and C710

[kevinm34232]

Re: Westinghouse SK-32H240S Continued problems

TV3: T3
TV4: T3
TV5: T2

I see a pattern here, Im out of transformers for the time being..

[budm]

Re: Westinghouse SK-32H240S Continued problems

The bad part is that one went out, the other may go out soon also.

[bpopilek]

Re: Westinghouse SK-32H240S Continued problems

Two Questions:

1. I see lots of replacement power supplies on eBay for this TV model. Only problem is that they don't look like the one I have in mine. The ones for sale have 6 individual transformers for the backlights, while mine has 3 dual inverters. Are they interchangeable or do I need the same one I already have?

2. If I can only use one like mine originally came with, any further tips for getting the 2sec to black resolved? I have replaced a fried transformer with a new one, and plugging each CCFL in individually, I can see that all 6 work. I also replaced the only cap that was bubbled, but that did not fix it either. Could it be something else causing it, or could I still have more bad caps even though they all look good with nice flat tops?

Thanks for reading!

[budm]

Re: Westinghouse SK-32H240S Continued problems

The board needs to be the same, your TV model may have more than one version sof the chassis or the LCD panel assembly, depends on which the manufacturers are.
Bad cap can look normal.
For example:
https://www.badcaps.net/forum/showth...ghlight=al2416

http://s807.photobucket.com/user/bud...?sort=3&page=1

[kevinm34232]

Re: Westinghouse SK-32H240S Continued problems

I will have at least 1 extra working power supply to sell as one of the screens got cracked.

[bpopilek]

Re: Westinghouse SK-32H240S Continued problems

I will have at least 1 extra working power supply to sell as one of the screens got cracked.

How much are you looking to get for the power supply?

[kevinm34232]

Re: Westinghouse SK-32H240S Continued problems

Dunno PM me if you want we'll discuss it.

[kevinm34232]

Re: Westinghouse SK-32H240S Continued problems

I have received 10 more transformers from China which I got much cheaper.. Replaced the first one and TV shut down backlight. Tried another transformer same thing. Tried another one of the TVs same thing.

Checked ohms readings on secondary windings they are all over the place. 3 were close on both sides, even those wouldn't keep TV on although they seem to test fine. I finally took a known good transformer and put it in the same place and it was fine.

I know there have been others who had same shutdown issue after transformer replacement so maybe same batch, beware... I guess you get what you pay for in this case..

[budm]

Re: Westinghouse SK-32H240S Continued problems

They may be rejected from factories and being sold as new.

[retiredcaps]

Re: Westinghouse SK-32H240S Continued problems

I have received 10 more transformers from China which I got much cheaper.

Complain to seller. You may get a refund or a new batch.

I have recommended and used ebay sellers for inverter transformers and I can't recall a case where it didn't work in 3+ years here. You, unfortunately, would be the first.

[bpopilek]

Re: Westinghouse SK-32H240S Continued problems

I am so frustrated! I purchased an entire set of 16 replacement caps to put on this board, and I am still getting the two seconds to black problem. I have also replaced a blown fuse, and a fried transformer. I do not see any other components on the board that have any signs of damage. Is there something I am overlooking? Could the new Transformer still be part of the problem, or could I still have another transformer that is bad but just hasn't totally fried yet? I am at a loss, and would appreciate any other thoughts or suggestions. Thanks!