Toshiba 42HL67 Missing 24v no backlight

[Glitcher]

Set plugged in, blinks yellow a couple of times then I can turn it on and the led turns green but there is no picture and no backlight.

Noticed there is a missing 24V on the PSU. I checked the fuses on both inverter boards and they checked good however there is no 24v across them either. Unplugged both inverter boards but there is still no 24v on the psu output

All the other voltages are present as labeled though. Anyone have a thought for this psu? PE0306

[Glitcher]

Re: Toshiba 42HL67 Missing 24v no backlight

There are two main filter caps, one measures 162v while the other one only measures 3v when plugged in standby.. When forcing the psu on with 5v connected to ps-on both those caps now measure 162v? I'm guessing a problem with the Pfc circuit?

[Glitcher]

Re: Toshiba 42HL67 Missing 24v no backlight

Looks like I just found an open fuse. Removed and replaced it with another to see if that was the only problem. Plugged it in and heard a loud pop and spark... Looked over and the cap nearby had exploded. However fuse is still good. Also the Main 120v AC fuse had popped

So is it just this cap or is it also something else? Anyone?

[budm]

Re: Toshiba 42HL67 Missing 24v no backlight

That is more likely the snubber cap for that multi-pin SMPS IC next to it. What is the P/N of that IC?

[Glitcher]

Re: Toshiba 42HL67 Missing 24v no backlight

Its labeled STR-Z4569

[budm]

Re: Toshiba 42HL67 Missing 24v no backlight

See if the cap is connected between pin 12 (Ground pin) and pin 14 (output), or pin 1 and pin 12. If not trace it out to see how that cap is connected in the circuit.

I cannot find the spec sheet for the IC yet, but here is how it is used:
https://cdn.badcaps-static.com/pdfs/...e37577fe93.pdf

[Glitcher]

Re: Toshiba 42HL67 Missing 24v no backlight

Looks like the cap is connected between pin 1 and pin 12.

[budm]

Re: Toshiba 42HL67 Missing 24v no backlight

OK, just measure the resistance on the two pads of the cap to see if it shows really low resistance, if it is OK then you can run without that cap for now for quick test.
Ceramic failed mode is shorted circuit, you can use the same value as shown in the diagram, 10,000pF (0.01uF) 500V minimum.

[Glitcher]

Re: Toshiba 42HL67 Missing 24v no backlight

Measuring the two pads of the cap seems its not shorted. It will rise resistance until off range for my meter each time i switch probe direction.

So after replacing the main AC fuse, I plugged it in again with 5v linked to ps_on. Everything seems the same as before besides the missing cap, all voltages present except the 24V. So I guess it initial problem was that ceramic cap shorted which blew the fuse next to it? and while replacing the fuse the cap finally blew since it was already shorted? So I just need to replace the cap?

I also noticed after replacing the fuse, the main caps will discharge now as before it would stay on 160v after I unplugged it for even a day.

[budm]

Re: Toshiba 42HL67 Missing 24v no backlight

"So I guess it initial problem was that ceramic cap shorted which blew the fuse next to it?" Yes.

So without the cap in place for now and the new fuse is in, you still do not get the 24V? That IC is the SMPS IC for generating the 24V.
I would connect every thing back in place an try again, just leave that cap out for now, and put in new fuse.

[Glitcher]

Re: Toshiba 42HL67 Missing 24v no backlight

Hey looks like its working! After I put the PSU back in the set, it powered right up. I was testing the PSU while out of the set, I guess maybe it needed the bl_on signal from the main board.

[budm]

Re: Toshiba 42HL67 Missing 24v no backlight

Great, now just have to get the new cap.

[Glitcher]

Re: Toshiba 42HL67 Missing 24v no backlight

Would I be able to replace that ceramic with a film capacitor? I have this one from my salvaged parts. 103J 630V

[budm]

Re: Toshiba 42HL67 Missing 24v no backlight

That will work.

[Glitcher]

Re: Toshiba 42HL67 Missing 24v no backlight

I thought that film caps were better for snubbing?
Just soldered in the cap, plugged everything in, turned on and no explosion
Looks like this one is good to go.

[budm]

Re: Toshiba 42HL67 Missing 24v no backlight

This cap is not used for the snubber, this one is for filtering, the snubber is one on pin 14 and pin 12.