toshiba 32av500u sound but no picture

[HotHead]

Hello again.
I have tried all inputs on the tv with the same results. Always sound with no picture. I did the flashlight test and do see a picture moving in the background and see the menu screen.
I have encountered this problem before with a different tv and the transformers on the inverter boards were shot.
Seems like the same thing here but before I go removing the two transformers(one on each board) is there a way to test them while still connected or should I test elsewhere before removing them? I also read that some of the 8 medium ic could be bad and should be replaced? Is there a way I can test these?
I believe I am going in the right direction but would like some guidance and help if possible.
I have posted some pics of the 2 inverter boards.

Also when I search for replacements transformers I cant seem to find the ones on the board, 331 70chk. Does anybody know why?
Thanks for any help.

[budm]

Re: toshiba 32av500u sound but no picture

First, do you see the backlights even flash on for seconds?
Do you have 24VDC Voltage and the BL-ON signal feeding the the inverter boards?
There are fuses on the inverter boards also plus the Power MOASFETs and filter caps that should be checked.
You can do the high voltage winding resistance comparison test between the two transformers.
How about the pictures of the whole back side of the TV so we can see how all the boards are connected together?

[HotHead]

Re: toshiba 32av500u sound but no picture

No I do not see any flickering from the backlights at all.
I do have 24 volts coming of the power supply that feeds the 2 inverter boards. Not sure if this is the BL-on.
I did an ohm test on the fuses(white ones next to connector on inverter coming from power supply) The master inverter fuse reads 0 and the secondary starts at 0 and climbs. I stopped when it reached .750 on 2000ohm setting.
The power moasfets are the 8 ic s? 4 on each board...Am I testing voltage on these?
The voltages winding resistance test you speak about would be with the transformer on board right? And not on the high voltage side, correct?

[HotHead]

Re: toshiba 32av500u sound but no picture

I also notice some scortch marks around the legs of the transformers. Is this normal?

[budm]

Re: toshiba 32av500u sound but no picture

"he master inverter fuse reads 0 and the secondary starts at 0 and climbs. I stopped when it reached .750 on 2000ohm setting."
Are you measuring the resistance of the fuse between its two ends, it should show about the same resistance as when you touch the two probes of your meter together.
The resistance of the inverter transformer is for the secondary side winding of the inverter transformers, not Voltage testing.

"The power moasfets are the 8 ic s? 4 on each board...Am I testing voltage on these?" The Power MOSFETs are those 4 devices with big metal tab on top and two legs on the bottom side, 4 on each board. You will check for low resistance between the Source pin and the Drain pin.
The backlights should flash on first on then if there is problem then the protection circuit will kick in, so i can be that the inverter board is not getting the BL-ON to turn on the inverter circuit.

[Saltfrog]

Re: toshiba 32av500u sound but no picture

I had the exact same problem with my 32av500u. Tv would power on with no flash or 2 seconds to black. Good audio and flashlight test showed an image. Both of my inverter boards looked good. I ordered a set on ebay for $35 and installed them. With the "new used" boards I did get the 2 seconds of screen light up and then back to black. I then swapped out my original master board and that solved the problem. Turns out I had a bad slave board and the set I bought had a bad master board. In the end I got $15 back and in the process learned that the slave board tends to be a problem in this tv.

On a side note to that- the tv worked great for a few weeks and then I lost the bottom 2/3 to half of the screen to black. This includes picture and menu. Swapped out the tcon board with a used unit and only got all vertical lines. I put my old tcon back in and got the same top 1/3 of picture to work. I'll probably follow up with my own post about my issue. Picture of my issue is attached.

[HotHead]

Re: toshiba 32av500u sound but no picture

Ok so here is what I got.
Multi meter set to Ohm/resistance setting 2k.
The fuse on the master inverter (f1 72v 5 amp) reads 0 as though I was touching the leads. The fuse on the slave board reads 0 also but starts to climp up to 1 like I said before.
The 8 Power MOSFETs (4 on each board fdd 8447l)
The 4 on the master board read nothing at all. Multi meter stays on 1. I'm testing the resistance on the 2 leads that are soldered to the board. There is a middle lead but it is not soldered to anything. Either way I get no reading on any of them.
The 4 on the slave board, 2 of them read 0 infinity(as though I'm touching the leads) and 2 of them give no reading at all.
Now for the transformer.
Master board. The 2 legs coming out of each side of the transformer give a reading of 0.
If I take a reading of a side leg and the third leg(on the end with 6 legs) I get a reading of .023.
The remaining 5 legs don't give any reading.
The 4 legs at the top end all give readings of 0.
The slave transformer gives all the same reading as the master except that none of the six legs give any reading.
I also re measured the voltages coming off the power board.
Had 24v on the p203 and p202 pins and also the 24v on pins 3-4, 12 volts on pins 8-9 and 5v on pin 16 for p201.

Not sure if I did all the testing correct but considering some of the differences found from board to board there is surely something going on.
I'm sure I should change all the 8 mosfets and one fuse(Master one?) but which transformer and where would I get one like it. My searches come up with nothing but full boards.
Thx guys.

[budm]

Re: toshiba 32av500u sound but no picture

"The fuse on the slave board reads 0 also but starts to climp up to 1 like I said before." Fuse is open = bad.
"The 4 on the slave board, 2 of them read 0 infinity(as though I'm touching the leads)" 0 is not infinity, it is shorted.
When you report the resistance readings, always put what is shown on the meter as in OHMS, K OHMS, or M OHMS.
I.E. 1 OHMS, or 1 K OHMS, that makes a big difference.

[HotHead]

Re: toshiba 32av500u sound but no picture

So then the reading on the transformer 331 70chk would be 223 ohm if the meter was set to 2k ohm.
If the second transformer on the slave board didn't give any continuity from the 3rd pin and side pin could this mean its bad also.
Does a reading of 223ohm on the first make sense?
Thanks for the info, pointers and corrections they are much appreciated.