Sony SMPS No backlight

[ljintexas]

I am gettiing signal from main. I am getting audio but no backlight. Both Q302 and D307 were shorted. I have a parts board that drives backlight but has an issue running more than an hour or two. Replaced Q302 and D307. Still no backlight. Transformer winding resistance is very similar, nothing way out of whack. I can buy a board but this is a learning opportunity.

Suggestions on next steps?

Thanks

LJ

[R_J]

Re: Sony SMPS No backlight

Have you checked R317, R314 & R316? Q301 could also be damaged.

[budm]

Re: Sony SMPS No backlight

Model of the TV will help.

[ljintexas]

Re: Sony SMPS No backlight

I am sorry Bud. It is a KDL40S4100 Sony Set.

[ljintexas]

Re: Sony SMPS No backlight

Half of the zener diodes in that section do not give me a tone and read over .7 volts forward. Is that normal? It's the same on both boards.

[ljintexas]

Re: Sony SMPS No backlight

Have you checked R317, R314 & R316? Q301 could also be damaged.

All of those show resistance values and Q301 tests good with a meter..also, all fuses in this area test good.

[nomoresonys]

Re: Sony SMPS No backlight

Have one of these working in the basement, with the back off, if you need any voltage tests for comparison let me know.

[budm]

Re: Sony SMPS No backlight

I asksed Dannyx to see if he can provide the info.
https://www.badcaps.net/forum/showthread.php?t=73237

[budm]

Re: Sony SMPS No backlight

All of those show resistance values and Q301 tests good with a meter..also, all fuses in this area test good.

Are you 100% sure that fusible resistor R317 is good and it shows really low Ohm?
Q302 for the inverter circuit tested a shorted, was it shorted between Gate and Drain?

[R_J]

Re: Sony SMPS No backlight

This should help

[Dannyx]

Re: Sony SMPS No backlight

I'll provide the original service documentation but it's for the 4000 model so take it with a grain of salt - Sony doesn't seem to provide any resources for the 4100 model specifically.

I once had an issue with a similar setup (except it was a Samsung I believe) where that "balancer" board on the left (left according to the manual at least) was powered by some transformers which looked like ordinary HV transformers...but they were located on the power board and there were HV leads running between the two board, so I thought "that's a freak setup...which one is the damn inverter ?!" Thanks to some of the wonderful people here I was straightened out and the whole principle of a "balancer" was explained to me better. I believe Budm was kind enough to provide some documentation on this.

The problem wasn't there however, instead: bad capacitor on the power supply - the big 450v one, as those HV transformers feeding the balancer are powered straight off the 400v PFC bus. True, it was a lot easier in my case since nothing was blown, the TV was having obvious trouble starting up and the cap was ever so slightly bulged, but here it's completely different...still, if you have a different board, try a swap on that cap just for the sake of it (and an ESR/capacitance test also for the sake of it). Good luck....CFLs need to die, I hate'em !

[budm]

Re: Sony SMPS No backlight

I think OP needs to provide the pictures of the whole backside of the TV showing all the boards.

[ljintexas]

Re: Sony SMPS No backlight

Are you 100% sure that fusible resistor R317 is good and it shows really low Ohm?
Q302 for the inverter circuit tested a shorted, was it shorted between Gate and Drain?

I will verify this evening Bud as well as put up a pic of all boards at once.
Q302 fail = all three legs shorted to each other

Thanks

LJ

[budm]

Re: Sony SMPS No backlight

I will verify this evening Bud as well as put up a pic of all boards at once.
Q302 fail = all three legs shorted to each other

Thanks

LJ

You need to verify that the parts connected between Gate of the MOSFET's and the Isolated Gate drive transformer (T302) are not damaged.
BTW, at this you do not even see the backlights flash on for seconds even though the BL-ON is present and you do have PFC Boosted Voltage of around 380 ~ 400VDC between the two legs of the main filter cap, correct?

[ljintexas]

Re: Sony SMPS No backlight

R317 reads 3 meg ohms and change in circuit.

[budm]

Re: Sony SMPS No backlight

R317 reads 3 meg ohms and change in circuit.

Well, R317 (white body) is bad then, in post 6 you indicated that it is tested good.

[ljintexas]

Re: Sony SMPS No backlight

You need to verify that the parts connected between Gate of the MOSFET's and the Isolated Gate drive transformer (T302) are not damaged.
BTW, at this you do not even see the backlights flash on for seconds even though the BL-ON is present and you do have PFC Boosted Voltage of around 380 ~ 400VDC between the two legs of the main filter cap, correct?

Nary a flash Bud. Yes BL-ON is present and I have 384 volts PFC voltage across main filter caps.

I have now replaced R317 which reads .2 ohms. Tested all resistors and diodes in the area between gate of MOSFETs and T302. Q301 and Q302 test good with meter.

I will give it a shot this evening and reinstall board.
Thank You very much for your help!

LJ

[Dannyx]

Re: Sony SMPS No backlight

At the end of the day it could be a bad lamp, though I believe it should at least flash or something.....

[budm]

Re: Sony SMPS No backlight

Nary a flash Bud. Yes BL-ON is present and I have 384 volts PFC voltage across main filter caps.

I have now replaced R317 which reads .2 ohms. Tested all resistors and diodes in the area between gate of MOSFETs and T302. Q301 and Q302 test good with meter.

I will give it a shot this evening and reinstall board.
Thank You very much for your help!

LJ

So the inverter circuit did not even try to fire up the lamps so you need to do more in-depth troubleshooting in the inverter section. You do have PFC Boosted Voltage, correct?

[nomoresonys]

Re: Sony SMPS No backlight

.