Olevia LT30HVS - Inverter Transformer

[aliasdck]

Got this TV off a guy on craigslist. His description of the problem sounded like it could likely be bad caps, so I took the plunge and bought the TV from him as is.

Got it home and plugged it in. Just as the TV comes out of standbye, the backlights would come on for a split second (during which, you can see a nice bright blue screen) then the TV shuts off.

No bulging caps in the power supply and power supply voltages were correct and solid. Decided to take it apart further so I could inspect the inverter board. I measured all the inverter transformers and sure enough, one of the transformers primary windings is completely open. All others are around 900 to 1k ohm.

Did some diggin around on the net and apparently this is a common problem with these boards.

The inverter board is a Darfon. Here is a pic from lcdparts of the board:

http://www.lcdparts.net/LCDTVInverte...ginal=V144-001

Anyone know where I can get one of these transformers? On the top, it is stamped with: 4009A448003 but Im not sure if that really means anything because a google search isn't coming up with anything.

[PlainBill]

Re: Olevia LT30HVS - Inverter Transformer

Got this TV off a guy on craigslist. His description of the problem sounded like it could likely be bad caps, so I took the plunge and bought the TV from him as is.

Got it home and plugged it in. Just as the TV comes out of standbye, the backlights would come on for a split second (during which, you can see a nice bright blue screen) then the TV shuts off.

No bulging caps in the power supply and power supply voltages were correct and solid. Decided to take it apart further so I could inspect the inverter board. I measured all the inverter transformers and sure enough, one of the transformers primary windings is completely open. All others are around 900 to 1k ohm.

Did some diggin around on the net and apparently this is a common problem with these boards.

The inverter board is a Darfon. Here is a pic from lcdparts of the board:

http://www.lcdparts.net/LCDTVInverte...ginal=V144-001

Anyone know where I can get one of these transformers? On the top, it is stamped with: 4009A448003 but Im not sure if that really means anything because a google search isn't coming up with anything.

"Sometime your bargain turns sour; sometimes you get lucky." 4009A is the part number, the rest is a production code or something like that. Double check your readings, the inverter I had had a covering of flux that made reading the resistance a little tricky.

These guys have the transformers. I've dealt with them, they seem to be good people. Better hurry, they only have 466 in stock.

PlainBill

[aliasdck]

Re: Olevia LT30HVS - Inverter Transformer

yea Ive doubled checked the transformer. Had problems getting a reading on a few of them so I was aware of that problem. Made sure to get good contact on the actual pin of transformer... not just the solder pad.

Just a few minutes ago I followed this guy's (holdentogether) advice over at rcgroups.com:

Ok I also have the nasty Dafron V144-001 inverter board in my 30" LCD TV I see a lot of other people are having problems with these.

I didnt fix it but I fooled it and It was easy. On the 20 pin oz960 which is a ccfl controller I noticed that pin 10 was rising and staying well above 2.75v thresehold,( more like 3.75v) this will allow the Backlight to start up for a second or two then turn off. The reason for this is pin 9 is low allowing the oz960 to not monitor overcurrent on start up. then as pin 9 rises in voltage pin 10 should be falling in voltage, but mine doesnt. So an easy fix is to put a LED from pin 10 to ground This holds pin 10 to around 2.4v, normal operating voltage.

http://www.rcgroups.com/forums/showp...5&postcount=74

I followed his advice just as a quick test and the TV Turned on and stayed on. I can see a darkened band across the tv right where the bad transformer's ccfl should be. I suppose that bulb could be bad, but I'm 100% sure this transformer's primary is reading open. Whereas the others are nearly identical.

But at the same time this confuses me a bit... as it sounds the function of all this is too turn the set off if an overcurrent is detected in the Inverter (which is at first disabled during the initial startup). A shorted transformer winding would cause an obvious overcurrent... but an open one? Not sure how that plays into his description of how his mod is working.

But then again, I haven't seen a pinout of that chip or a schematic of the board so I can only make assumptions about his idea and whats really going on.

[PlainBill]

Re: Olevia LT30HVS - Inverter Transformer

yea Ive doubled checked the transformer. Had problems getting a reading on a few of them so I was aware of that problem. Made sure to get good contact on the actual pin of transformer... not just the solder pad.

Just a few minutes ago I followed this guy's (holdentogether) advice over at rcgroups.com:



http://www.rcgroups.com/forums/showp...5&postcount=74

I followed his advice just as a quick test and the TV Turned on and stayed on. I can see a darkened band across the tv right where the bad transformer's ccfl should be. I suppose that bulb could be bad, but I'm 100% sure this transformer's primary is reading open. Whereas the others are nearly identical.

But at the same time this confuses me a bit... as it sounds the function of all this is too turn the set off if an overcurrent is detected in the Inverter (which is at first disabled during the initial startup). A shorted transformer winding would cause an obvious overcurrent... but an open one? Not sure how that plays into his description of how his mod is working.

But then again, I haven't seen a pinout of that chip or a schematic of the board so I can only make assumptions about his idea and whats really going on.

Virtually every inverter controller contains circuitry that will monitor the state of the CCFLs. Characteristics being monitored include current through the CCFLs, drive current for the transformers, and voltage out of the inverter transformers. It's a trivial* task to multiplex the various voltages onto a single pin.

*Trivial = half a dozen components per CCFL per parameter.

PlainBill

[aliasdck]

Re: Olevia LT30HVS - Inverter Transformer

Virtually every inverter controller contains circuitry that will monitor the state of the CCFLs. Characteristics being monitored include current through the CCFLs, drive current for the transformers, and voltage out of the inverter transformers. It's a trivial* task to multiplex the various voltages onto a single pin.

*Trivial = half a dozen components per CCFL per parameter.

PlainBill

Makes perfect sense, but I didn't want to be making too many assumptions.

Just ordered the transformer from that site you posted. Thanks for your help.

I'll report back with the results.

[aliasdck]

Re: Olevia LT30HVS - Inverter Transformer

Its fixed



Thanks for the help plainbill.

The transformer I got from that site you posted measured only 700 ohms while the others measure around 900 (out of circuit). I was concerned that this would cause problems (but since it works Im assuming it has the same number of turns but possibly the wire is of a different conductance). Either way I'm happy.

Unfortunetly I damaged one of the solder pads while removing the old one and had to resort to installing a few jumper wires. This was my first time removing a surface mount component... a learning experience it was.

I heated each leg individually with my solder iron. At the same time I inserted a sharp knife under the leg and bent it up and away from the pad. On the last leg I didn't notice there was a small blob of solder still connected, so when I pulled the transformer loose it took the pad and a few mm's of traces with it . For future reference, is there a better way to do this (poor mans way... only have access to a solder iron and regular bench tools)?

Again, thanks again.

[tmwalsh]

Re: Olevia LT30HVS - Inverter Transformer

chip-quik is a 'brand name' metal that will mix with regular solder, and the resulting amalgam(?) has a lower melting point than real solder, so you can almost use a hair dryer to melt the solder and remove the chip. The other alternative is copper braid that is ;fluxed'. Push the braid onto the leads, and heat. The braid will absorb the solder.

I do NOT claim any sort of expert status in this, and have pulled up more than my fair share of traces, even doing standard old style components.
tom

[PlainBill]

Re: Olevia LT30HVS - Inverter Transformer

Chip Quik is my preferred method. On one hand a small coil of the stuff will set you back over $10. On the other hand, a small coil goes a long way.

I noted the same difference in resistance, but of course the number of turns (or more correctly, the turns ratio) is the important parameter.

PlainBill

[JonathanAnon]

Re: Olevia LT30HVS - Inverter Transformer

Hi guys, sorry for digging up and old thread, but I happened to be working on the same TV.... That little trick, with the LED and pin 10 of the chip on the inverter board, works like a charm.... Seems that the secondary side of one of the inverter transformers is open circuit .. (all the rest measure 2K)... The LED trick gets the TV up and running, but I'm gonna have some job trying to find that transformer.

[budm]

Re: Olevia LT30HVS - Inverter Transformer

I got mine years ago from LCDPARTS.NET. May be alot cheaper on EBAY now