Sony SMPS No backlight

[ljintexas]

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.....

Actually what is now my parts board, ran the tv with both audio and video but would cut off after 90 min or so and would not react to on board power sw or factory remote. After 12-24 hrs it would start up and run again until it would just go dead.

[ljintexas]

Re: Sony SMPS No backlight

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?

I have not reinstalled the board since replacing R317

[Dannyx]

Re: Sony SMPS No backlight

What is this "parts board" you're referring to: a main board or a power supply ?

[nomoresonys]

Re: Sony SMPS No backlight

Think these suffer from overheating, mine would not run with the back on for very long, so I left it off, no problems since, its been 4 years now of daily use.

[budm]

Re: Sony SMPS No backlight

I have not reinstalled the board since replacing R317

Oh OK, so we will wait to see the result then.

[ljintexas]

Re: Sony SMPS No backlight

What is this "parts board" you're referring to: a main board or a power supply ?

I have two SMPS boards..I used to have three but the wife deep sixed the oldest one. The one that was originally in the set is what we are working with now. It would produce audio, but no back light..
Q302, D307 and R317 were shot. I replaced them all..with components from parts board that all test good..out of circuit and in. Time for the smoke test!!

[ljintexas]

Re: Sony SMPS No backlight

Upon power up, loud pop and bright spark in the vicinity of T302. All components replaced are still good. Fuses all still good..L800 seems to be shorted and is in circuit with main caps. In circuit, main caps test 350 uf when they are really 180uf. Time to remove main caps and test??

[ljintexas]

Re: Sony SMPS No backlight

Pic

[Dannyx]

Re: Sony SMPS No backlight

Upon power up, loud pop and bright spark in the vicinity of T302.

That sounds pretty bad. Not sure what T302 actually does exactly, as I'm not sure what A_OUT and B_OUT refer to, but I see a handful of components nearby that could've gone pop....they need to be checked.

L800 seems to be shorted and is in circuit with main caps

That is the PFC boost coil. It SHOULD read shorted, so to say, on your standard DMM in continuity mode, as it's essentially a piece of wire wound around a ferrite coil - doesn't present a high enough resistance for the meter to read it.

That said, if the set still works (with no backlight) after all of this, we can conclude the primary is (still) OK.

Were the caps tested in circuit or out ? If they're already out, might as well replace them and cross-check with the known "good" ones.

[R_J]

Re: Sony SMPS No backlight

Is R317 still good? If Q302 & D307 were bad, you have other components in that area that are also bad.

A_OUT and B_OUT refers to the drive from IC706, IC706 (18,19) It drives T302

[budm]

Re: Sony SMPS No backlight

T302 is the Gate drive isolation transformer.
If something pop or spark then you should be able to see what parts are damaged.

[ljintexas]

Re: Sony SMPS No backlight

T302 is the Gate drive isolation transformer.
If something pop or spark then you should be able to see what parts are damaged.

There was aloud pop and a visible spark on the left side of the board near T302 and L800. I cannot find any visible damage nor do any components in that area test bad with a meter..other than L800..testing 3 &4 to 1&2 reads .3 ohms.
Testing 5&6 to chassis read 6 Meg Ohms. Testing 5&6 to the negative side of C801 or C802 reads .4 ohms.

[ljintexas]

Re: Sony SMPS No backlight

Is R317 still good? If Q302 & D307 were bad, you have other components in that area that are also bad.

A_OUT and B_OUT refers to the drive from IC706, IC706 (18,19) It drives T302

R317, Q302, and D307 are all still good after the pop. Q301 tests good with a meter as does D309.

[ljintexas]

Re: Sony SMPS No backlight

In comparing readings...it would appear that on the parts board which would run the set for an hour or so,then go completely dead, Q800 and D800 test bad with a meter.

[ljintexas]

Re: Sony SMPS No backlight

Is R317 still good? If Q302 & D307 were bad, you have other components in that area that are also bad.

A_OUT and B_OUT refers to the drive from IC706, IC706 (18,19) It drives T302

Could the shorted MOSFET, and Diode have damaged IC706?

[R_J]

Re: Sony SMPS No backlight

IC706 is not likely damaged, but IC801 might be damaged by the shorted Q800

[Dannyx]

Re: Sony SMPS No backlight

IC706 appears to be isolated via T302 so it shouldn't technically be bad after that pop....most likely there's something bad on the primary still. Did the fuse go ? Is the set at least powering on with no BL in this state ?

[ljintexas]

Re: Sony SMPS No backlight

IC706 appears to be isolated via T302 so it shouldn't technically be bad after that pop....most likely there's something bad on the primary still. Did the fuse go ? Is the set at least powering on with no BL in this state ?

All fuses are good. It popped as soon as I applied power so I disconnected it asap. I can try again. Could there be a short between the layers of the board as I have no physical evidence of the spark/pop.

[Dannyx]

Re: Sony SMPS No backlight

It's not a multi-layer board by the looks of it. That transformer itself could've popped for various reasons (windings broke down internally) if you really can't identify any marks. You're suffering the same annoyance as me and my Tyco supply I wrote a post about - I saw a spark but couldn't find what caused it....

You could cross-check the transformer with the other one which is presumably OK.

At least blow it for good so you know what popped That's how I sometimes do it

[R_J]

Re: Sony SMPS No backlight

Remove R317 and check that the pfc circuit is working, If it is then recheck the parts in the backlight supply circuit. Use a 60 watt incandescent lamp in series with the a/c cord to limit the current if there is a short. If the lamp lights bright, there is a short, if it lights slightly and goes dim it should be ok to do further testing.