Dynex TV power supply

[whaase]

I have a TV I'm trying to fix. I do know a bit about electronics, but not a lot The power supply is making a weird buzzing sort of sound and will eventually shut off until it cools down. The TV works great otherwise.

It sounds like the buzzing is coming from the bridge rectifier. While I was probing around, I did get a bit of a shock from heat sink that the rectifier is on. It meters out ok though which is confusing to me lol

I tested the output voltages and my 24v is all over the place.

I will post a link to a small video of the sound, right click and save as

http://whaase.com/walter/tv-prob.mp4

Any help would be appreciated

Dynex 46" LCD from 2011.
Model is DX46L262A12


Walter

[budm]

Re: Dynex TV power supply

"It sounds like the buzzing is coming from the bridge rectifier. While I was probing around, I did get a bit of a shock from heat sink that the rectifier is on. It meters out ok though which is confusing to me lol" That heatsink is at line Voltage so be careful not to touch anything with your hands or body, you should at least plug what ever you are working on into GFCI outlets.
Please up load good clear pictures of the whole back side of the TV and the boards.

[stj]

Re: Dynex TV power supply

if the 24v is all over the place then probably the caps are stuffed and the diodes or coils are resonating.

[budm]

Re: Dynex TV power supply

BTW, I listen to that sound, it is like something in the PFC circuit. Will wait for the pictures of all the board, especially the main filter cap.

[whaase]

Re: Dynex TV power supply

I did check most of the caps out of circuit and they seemed to test good. None of them look bulged in anyway (I know that doesn't always mean they are not bad)

I will post pictures shortly

Thanks, Walter

[budm]

Re: Dynex TV power supply

So you have ESR meter for testing the caps?

[whaase]

Re: Dynex TV power supply

So you have ESR meter for testing the caps?

I removed the caps from the board and tested with my multimeter.

I have a few pictures. I can get more tonight if needed.

I will also included the service manual

[budm]

Re: Dynex TV power supply

You need ESR meter.

[newtothis]

Re: Dynex TV power supply

No ESR meter = Change caps anyway for piece of mind

[whaase]

Re: Dynex TV power supply

I will be replacing all the caps. I'm not sure why I would need an ESR meter if I take the caps out and test them with my multimeter? I do have capacitance testing on my multimeter.

am I missing something?

[ljintexas]

Re: Dynex TV power supply

I have found more that fail ESR test than capacitance test. They looked fine and tested fairly close to the right value capacitance wise.

[budm]

Re: Dynex TV power supply

See PDF's.

[stj]

Re: Dynex TV power supply

there are 3 things to test on a capacitor.
capacitance, ESR and ripple current

multimeters can only test capacitance.
only very specialised equipment i'v not seen in years can meter the ripple current.

[budm]

Re: Dynex TV power supply

Leakage (current) also.

[whaase]

Re: Dynex TV power supply

Ok, I'm going to order all the capacitors I need. Should I also replace transistors?

Walter

[budm]

Re: Dynex TV power supply

Beside the 24VDC output for the inverter not steady, how about other Voltages?

[whaase]

Re: Dynex TV power supply

24v were all over then faded away, 12v just slowly dropped and the 5v was solid.

[budm]

Re: Dynex TV power supply

The 12V and 24v are generated by the same power transformer so something in the 12V/24V SMPS is not working right, but we need to make sure that the PFC Voltage booster is OK first, so you need to check the DCV between the two legs of the main 450VDC filter cap to see if it is >360VDC and steady.
It is similar to the problem with this one:
https://www.badcaps.net/forum/showth...978#post549978

[kc8adu]

Re: Dynex TV power supply

i see a 250v cap.and looks like a pfc section.
error or nonstandard design?

[budm]

Re: Dynex TV power supply

i see a 250v cap.and looks like a pfc section.
error or nonstandard design?

I just notice that too, the PFC Inductor and the MOSFET & the DIODE mounted on the heatsink right next to it also.
SJ site is not working right now for me to see the board.