Westinghouse SK-32H240S Continued problems

[retiredcaps]

Re: Westinghouse SK-32H240S Continued problems

I followed PlainBill's advice by
testing the CCFL's by unplugging all but one connector and powering it up in a dark room. I did this for all six connectors and had a flash for each one.
So I assume all six lamps are working.

PlainBill's test above is only valid if the ccfl is completely broken. If the ccfl is completely physically broken, then it won't light. A ccfl can still light up and be bad because it is drawing too much current (i.e. it is near its useful life) or the return wiring is frayed internally.

A inverter PWM IC operates as an "all or nothing". Either all the ccfls work or none at all.

2 seconds to black can be

a) bad caps
b) bad ccfls
c) bad ccfl wiring (especially the return wiring)
d) bad secondary windings on the inverter transformer

More details starting with post #19 at

https://www.badcaps.net/forum/showthread.php?t=10419

Also, see budm's Inverter tester using old CFL

https://www.badcaps.net/forum/showthread.php?t=19987

[Mike95inNJ]

Re: Westinghouse SK-32H240S Continued problems

I received the replacement transformer today and replaced it but unfortunately it did not fix the problem. I followed PlainBill's advice by
testing the CCFL's by unplugging all but one connector and powering it up in
a dark room. I did this for all six connectors and had a flash for each one.
So I assume all six lamps are working. I could see each individual lamp light
up on the screen as well. Same symptoms as described by Xavier Renowned.
Westinghouse logo shows up, goes black, backlights come back on then goes black. Is it possible that the burn mark from the fried transformer ruined the pcb itself? Any advice would be helpful.
Thanks, Mike

[Mike95inNJ]

Re: Westinghouse SK-32H240S Garbage picked yesterday.

I found this yesterday morning being tossed to the curb. I found this post and I'm glad I did. These forums are always helpful to me when trying to fix a discarded lcd/plasma tv. This was a two seconds to black tv. I saw the three bulging caps right away and thought to myself I'd have it up and running in no time. Then I got a closer look and saw the fried transformer. If I had'nt read this I would've never known about these known issues and just want to say thank you to everyone that posts replies to help out noobs like me when it comes to trying to bring a tv back to life. I ordered the transformer I found on ebay for $9.69 free shipping from China. Just have to wait a couple of weeks for delivery. I hope the pcb itself isn't ruined by that nasty burn mark.
I already replaced the bad capxcon caps. I'll post a followup after replacing the transformer. Thanks again for all the expertise offered here. I appreciate it.
Take care, MikeinNJ

[Xavier Renowned]

Re: Westinghouse SK-32H240S Continued problems

That capacitor is 2200 uf and 10v I replaced this one too, but the new one is too big for the heat sink bridge plate now and there isn't space to lay it on its side. sorry haven't been on since Nov. busy Christmas season.

[Dgtech]

Re: Westinghouse SK-32H240S Continued problems

CRAP!!! Now I caught a snag with this TV. There is a capxon at location C709 (inside the two heatsinks). It had the white glue on it covering the value. When I lifted it up from the board, the glue snatched off the plastic covering with the value. I need to know what this cap is. I tried to find a schematic or parts list with no luck.

[PlainBill]

Re: Westinghouse SK-32H240S Continued problems

As kc8adu said, it's the most practical way to identify a transformer with an open or shorted secondary (it is highly unlikely there would be an open primary).

A much better method would be a ring tester, but that is a rather specialized piece of equipment that most hobbyists won't have.

PlainBill

[kc8adu]

Re: Westinghouse SK-32H240S Continued problems

beause you will find the bad one open or many shorted turns.stands out from the others.made in the same batch they should all be close.

So, why does transformer resistance matter so much when identifying faulty inverter transformers? (Noob here!)

[tom66]

Re: Westinghouse SK-32H240S Continued problems

Do the math. The typical CCFL draws about 4 - 6 ma at 800 - 1200 volts. Taking the worst cases (6 ma, 800 volts, 150 ohm difference), the variation is only .9 volts, about .1%

PlainBill

So, why does transformer resistance matter so much when identifying faulty inverter transformers? (Noob here!)

[PlainBill]

Re: Westinghouse SK-32H240S Continued problems

Same here - I've replaced a 4010A which read about 100 ohms below all the others, but it worked fine. I thought the resistance was part of how they balance the current in each bulb, so I was surprised it worked...

Do the math. The typical CCFL draws about 4 - 6 ma at 800 - 1200 volts. Taking the worst cases (6 ma, 800 volts, 150 ohm difference), the variation is only .9 volts, about .1%

PlainBill

[tom66]

Re: Westinghouse SK-32H240S Continued problems

Agreed, no guarantees, but there is one indication. I've replace a 4006A type transformer, the secondaries read about 950 ohms. On the replacement the secondaries read somewhat lower - around 800 ohms as I remember. Yet the new transformer worked perfectly. The only conclusion is the 'after market' transformer has the correct turns ratio, but heavier gauge wire - which should be less likely to break.

PlainBill

Same here - I've replaced a 4010A which read about 100 ohms below all the others, but it worked fine. I thought the resistance was part of how they balance the current in each bulb, so I was surprised it worked...

[PlainBill]

Re: Westinghouse SK-32H240S Continued problems

For this reason, I will replace all three but then again, there's no guarantee.

Agreed, no guarantees, but there is one indication. I've replace a 4006A type transformer, the secondaries read about 950 ohms. On the replacement the secondaries read somewhat lower - around 800 ohms as I remember. Yet the new transformer worked perfectly. The only conclusion is the 'after market' transformer has the correct turns ratio, but heavier gauge wire - which should be less likely to break.

PlainBill

[Dgtech]

Re: Westinghouse SK-32H240S Continued problems

On the OTHER hand, I worry that another will fail and my customer will be unhappy.

PlainBill

For this reason, I will replace all three but then again, there's no guarantee.

[PlainBill]

Re: Westinghouse SK-32H240S Continued problems

It's a shame; the inverters otherwise are a good design (quality caps, good layout & easy to replace the transformers.)

I've got mixed feelings, Once you have the concept, troubleshooting them is easy, and the cost to repair is minimal. On one hand, I'm happy because it was an easy fix. On the other hand I feel sorry for the original customer. On the OTHER hand, I worry that another will fail and my customer will be unhappy.

PlainBill

[tom66]

Re: Westinghouse SK-32H240S Continued problems

And from the variety of types that fail, it's not a bad batch, but a systemic problem (poor quality wire, poor winding technique, or both).

PlainBill

It's a shame; the inverters otherwise are a good design (quality caps, good layout & easy to replace the transformers.)

[PlainBill]

Re: Westinghouse SK-32H240S Continued problems

Yes those Darfon transformers seem to die all the time.

And from the variety of types that fail, it's not a bad batch, but a systemic problem (poor quality wire, poor winding technique, or both).

PlainBill

[tom66]

Re: Westinghouse SK-32H240S Continued problems

Yes those Darfon transformers seem to die all the time.

[retiredcaps]

Re: Westinghouse SK-32H240S Continued problems

Where is a good place to find them.

$10 on ebay + free shipping.

http://www.ebay.com/sch/i.html?_nkw=4301+transformer

lcdparts.net also has it, but it is 3x the price.

http://lcdparts.net/TransformerDetai...ProductID=2774

[Dgtech]

Re: Westinghouse SK-32H240S Continued problems

I have the same TV and the same problem. I bought this today from someone who had this problem before. They replaced one of the three transformer on the inverter board as it burned the board open. This time (about three months later) it was the transformer on the oposite side of the board that burned open.
Is this a bad batch of transformers? Should I replace all three to be on the safe side? Where is a good place to find them.

Pics below.

I should also mention that resistance checks have been done and they look ok - the ones that weren't burned.

[PlainBill]

Re: Westinghouse SK-32H240S Continued problems

I have been working on a 32" Westinghouse TV and so far I have replaced the inverter transformer and some of the badcaps that I found.

What is unusual is that after replacing the bad components the TV still won't work. When I turn it on it shows the logo then goes black, then, if I leave it on the picture will show up for a second, then goes black again.

The capacitors I replaced may not be the right ESR or ripple current rating.

The old caps were CapXons and the two I replaced were a 2200uF 10v GF 105 C P733 VENT, and a KY 16 v 1000uF (M)105 C 7(7) 8e. Any Links fro finding the specs for these caps would be greatly appreciated. Replaced with 2200 uF, PL(M) nichicon and a 1000 uF FM Matsushita Panasonic cap.

I also replaced a 5D 3KV, blue ceramic capacitor that was reading 9 pF instead of 5 pF

In the pictures i have circled the parts I replaced and would like to know where to go next in trouble shooting this board?

This appears to be and should be troubleshot as 'two seconds to black'. The pictures aren't very good, and without a picture of the bottom of the power supply / inverter it's going to require a little extra work. Since you will be doing the work, I don't mind.

The following tests should be done in as dark a room as possible - you are going to be looking for a brief flash from the backlights.

Set everything up so you can see the back of the LCD panel. There are usually enough light leaks that you can see if the backlights are on even from the back.

Disconnect all of the cables to the backlights except one. Turn on the TV. You should see a brief flash before the protection circuits kick in. Turn the TV off, unplug the first CCFL and plug in the next. Turn on the TV and watch for the flash. Repeat for each of the remaining 4 CCFLs.

With luck, all of the CCFLs except one will light. If none light, repeat, but hooking up a pair at a time, rather than only one.

Report your results.

PlainBill

[Th3_uN1Qu3]

Re: Westinghouse SK-32H240S Continued problems

Could be the CCFL lamps. Do you have another known good inverter you can use to test?