Need INVFT320A Inverter

[dkneyle]

This is an inverter used in a range of 32 inch CFL TVs. Mine has an open transformer winding. Thought maybe someone had one in the bottom of their parts drawer? Or maybe even the transformer, which has a part number of IT-133 06CK typed on it.

There is one on FleaBay for A$50 landed in Oz, so if I can't pick up a bargain somewhere, then I'll probably buy that one. Only just makes it an economical repair.

Ironically, I stripped down the same model for scrap a couple of years ago and I sold the inverter! When fault finding today's TV I had no PS-On signal from the mainboard. I'd saved the previous mainboard because I was unable to confirm it was functional. Dropped it into this current repair and everything came up except the backlights. Flashlight test showed all other systems functional, voltages to inverter were correct. Troubleshooting inverter led to the conclusion the transformer had failed.

[budm]

Re: Need INVFT320A Inverter

So one of the two inverter transformer has open winding on the high Voltage side?

[dkneyle]

Re: Need INVFT320A Inverter

I'm assuming it's the high voltage winding, although the companion transformer winding reads ~3 ohms which suggests perhaps it's a primary winding? Very hard to trace circuit as the transformer tracks are whited out. I do have a schematic so I'll pull that out and see if I can find how the windings are configured. BTW, the fuse on the board is OK.

[budm]

Re: Need INVFT320A Inverter

You have two transformer drive circuits (4 MOSFETs per transformer). So even if you have one bad transformer you should see the backlights from the good transformer come on for seconds before the protection circuit kicks in.
We need good clear high res straight shot pictures of the board to see how the circuits are laid out on the board.

[dkneyle]

Re: Need INVFT320A Inverter

The manual does not include a circuit diagram for the inverter. The reverse side of board has no tracks. I suspect it is a multi layer board. I've tried to indicate in the pics the discrepancy I was measuring.

[budm]

Re: Need INVFT320A Inverter

OK, thanks for the pictures.
The set of four MOSFETs are connected in parallel, the primary winding of the inverter transformers are connected in series, the drive circuit for the primary winding is Half-bridge drive.
At this point I would remove that suspected transformer and look at the bottom side to side what condition it has and that will also show us how the HV winding is connected to the legs of the transformer.

[dkneyle]

Re: Need INVFT320A Inverter

It's the strangest thing Bud. I can't get any continuity on the secondary side of those transformers. I mean, I know how a transformer is configured. There's 6 tabs coming out of the transformer; 3 aside I'm assuming. On the primary side I get a very low DC ohms reading across two of those tabs (the upper two in the image shown in post above). No apparent connection on the third tab. But apart from that, nothing on any other tab. Nothing on the secondary side. And it's the same for both transformers. Got me thinking I didn't know how to use a meter! I de-soldered one of those transformers but no secrets were revealed. The power FETs check out OK.
I will buy a secondhand board as a replacement. I'll post up the readings I get on those transformers just so people who might track down this thread for their own fault finding purposes are able to see the outcome.

[budm]

Re: Need INVFT320A Inverter

Can I see good clear pictures of the bottom side of the transformer?

[dkneyle]

Re: Need INVFT320A Inverter

I'll get those pics to you tonight (our time) when I go home from work.
The CFL tubes must be in series as there is only one wire from each HV outlet socket. So the secondary coils must be in series I would assume to be able to work and complete the circuit?

[budm]

Re: Need INVFT320A Inverter

I'll get those pics to you tonight (our time) when I go home from work.
The CFL tubes must be in series as there is only one wire from each HV outlet socket. So the secondary coils must be in series I would assume to be able to work and complete the circuit?

No, they are not in series, if they are, it will take very very high Voltage to fire up the lamps and to sustain the lamp to stay on.
What is the LCD panel P/N? It may have circuit board with Ballast cap per each lamp (and then parallel connected) if it uses CCFL, if it use EFL then the lamps will be connected in parallel without Ballast cap for each lamp.

[dkneyle]

Re: Need INVFT320A Inverter

Counting the transformer tags from top left in a counter-clockwise direction, 1 & 2 are the primary windings with virtually 0 DC ohms. The secondary appears to be 3 and 5 with a ~15 DC ohms. 4 and 6 appear not connected and are probably mounting supports?
Both transformers measure the same. Not sure why my initial measurements suggested a bad TX?
I have ordered another board (listed as "new" but I doubt it).
I'm wondering about my initial diagnosis? I had a TV that wouldn't start. I exchanged with a mainbaord I had lying around and it fired up and the flashlight test showed an image. I thought I measured a Power On voltage at the inverter along with the 24 volts required to power the board, so I made an assumption of a crook inverter. Now I'm wondering?

[dick_barton]

Re: Need INVFT320A Inverter

I would expect the primary and secondary windings to terminate on opposite ends of the transformer. In an earlier post you showed 3 ohms between the ends of one of the transformers. If you measure those two points on the board and or the transformer is it still 3 ohms?

[budm]

Re: Need INVFT320A Inverter

One thing we do not know is that if you are getting the BL-ON signal or not.

[Andrew F. Ali]

Re: Need INVFT320A Inverter

One thing we do not know is that if you are getting the BL-ON signal or not.

Check whether you have BL-ON or not. Perhaps you may have a bad CCFL. Consider another possibility IF you have a bad CCFL.....Converting to LED backlight.

[budm]

Re: Need INVFT320A Inverter

https://www.badcaps.net/forum/attach...1&d=1489211243

The ON/OFF pin is the BL-ON pin so check and see if it has >2.5VDC when TV is ON.
Might as well check the IN and EX dim pis also.
I was assuming that you had already check those signal since you seem to know about the PS-ON so I would think you will know about other signals as well.

[dkneyle]

Re: Need INVFT320A Inverter

The transformer has IT-133 06CK printed on it.
The reason I was prepared to purchase a complete new board was because I did measure BL-On and it was about 3.5volts. I had good 24 volt supply, no sign of CFL's firing and then going off after 2 seconds. In the past when repairing TVs I've seen these symptoms, realised it was a SMT board that was essentially too difficult for me to fault find and/or repair, so just bit the bullet and ordered another board.
I really should go to the effort of replacing that TX and checking if I actually have high voltage or not at the output. It could be CFL failure I suppose?
Now I'm on my learning curve. Explain what the IN and EX DIM lines do, where they are driven from, etc?

[Andrew F. Ali]

Re: Need INVFT320A Inverter

Should IN be EN and EX DIM be P-DIM? Look again at the jack and see if you have another pin with the label PWM, P-DIM or ADJ. You have 24Vdc and BL-ON. So all you need to get is 4 LED strips and the Universal LED Driver Bd and you are well on your way to convert to LED, as an alternative.

[Andrew F. Ali]

Re: Need INVFT320A Inverter

No post

[vinceroger69]

Re: Need INVFT320A Inverter

Should IN be EN and EX DIM be P-DIM? Look again at the jack and see if you have another pin with the label PWM, P-DIM or ADJ. You have 24Vdc and BL-ON. So all you need to get is 4 LED strips and the Universal LED Driver Bd and you are well on your way to convert to LED, as an alternative.

what does the picture on the tv look like after this conversion as the leds will not have diffuser lens fitted over them like on proper strips

[budm]

Re: Need INVFT320A Inverter

https://www.badcaps.net/forum/attach...1&d=1489211243
As labeled on the board:
IN-PW?(M) = Internal PWM dimming
EX-PW?(M) = External PWM Dimming
ON/OFF = BL-ON BACKLIGHTS ON/OFF
These signal are from the main board.
the Dimming control signal will one of the two but not both.