Dynex DX-LCD32, with no power

[wfdbackdraft]

I'm new to this forum, and new to TV repair so bear with me. I've fixed a few with bad caps, but this one is more involved.

It's a Dynex DX-LCD32. It's not the one with the "-09" either. That one looks different inside. I picked this one up cheap because it doesn't power on. The guy did say that it would work every now and then, but I haven't seen it yet. I plug it in, and get the orange stand-by light. Press power and the light turns to a solid green. No picture or any sounds. To get it back to stand by mode, I have to press power twice, and get orange flashes. It's really quick, and I tried to count. I either got 9 flashes, or a few times it does abut 15, then stays a solid orange.
I've looked at every capacitor and none are bulging.
I have a digital multimeter, and am ready to check whatever that you tell me. Keep in mind that I have very little knowlege of electronics but am willing to learn. I've enclosed some photos of the boards.
Thanks for any help that you guys can give me. I'm not looking to get into the business, just trying to get a decent TV for the garage.
Michael

[tom66]

Re: Dynex DX-LCD32, with no power

Are there any markings on the cable going from the PSU to the main board?

If so, check the voltages on the pins match these markings.

I notice one Rubycon cap and a few Chemicons - did you replace these or did someone else? (Or are they factory originals?? That would be very surprising...)

[wfdbackdraft]

Re: Dynex DX-LCD32, with no power

I did check those voltages on that side of the PSU, and here is what I got:

Red and Orange both have 13.2v, and were marked 12v on the board. Yellow and Green both have 5.1v and are marked as 5v on the board. The only other marking was what looked like 1 15v. Not sure if that was supposed to be 1v and 15 v, or what. But neither wire had anything. These wires are going to that small rectangle board. There were 3 wires with no markings on the board but had current. White 2.7, Black 4.0, and Brown 3.1. These were going to the main board.
And all of these readings were with the green power light on.
I also checked the other output on the PSU and got nothing except .1 on the wire marked dim on the board.

[wfdbackdraft]

Re: Dynex DX-LCD32, with no power

And I haven't replaced anything, and as far as I know neither did the previous owner. He never mentioned it.

[tom66]

Re: Dynex DX-LCD32, with no power

The 12V lines measured 13.2V? That's rather high... Something doesn't seem right. Where were you measuring ground?

[wfdbackdraft]

Re: Dynex DX-LCD32, with no power

At the chassis ground screw.

[wfdbackdraft]

Re: Dynex DX-LCD32, with no power

Even using the wire in that plug that is labeled GND, I still get 13.2 on those wires.

[retiredcaps]

Re: Dynex DX-LCD32, with no power

The 12V lines measured 13.2V? That's rather high...

From the computer lcd monitor world, a lot of the secondary voltages are unregulated and appear high, but then fall into "spec" when everything is working (i.e. there is a proper load).

It may be the same in the TV world especially since the backlights are not on to draw any load.

[tom66]

Re: Dynex DX-LCD32, with no power

That may well be true - although it's not typical for a supply with standby power.

Sometimes a higher voltage is indicative of bad caps because the power supply controller is overshooting or is unstable.

[retiredcaps]

Re: Dynex DX-LCD32, with no power

That may well be true - although it's not typical for a supply with standby power.

Sometimes a higher voltage is indicative of bad caps because the power supply controller is overshooting or is unstable.

I agree with everything you are saying. Just sharing what we have seen in the lcd computer monitor world.

[tom66]

Re: Dynex DX-LCD32, with no power

I agree with everything you are saying. Just sharing what we have seen in the lcd computer monitor world.

Yes, I have seen similar situations with computer power supplies, with no load voltages sometimes being quite high, above nominal ratings.

In my experience (and that of others on this forum) the #1 failure mode with bad caps is a decrease in output voltages, not an increase, although a capacitor decreasing in capacitance, or one with an extremely high ESR would probably cause an increase in voltage. Effectively, at high frequencies, the cap is supposed to act as a short circuit, to filter out the higher frequencies, but if it doesn't have a low enough ESR, there is no where for this high frequency noise to go, other than to increase the output voltage.

[PCBONEZ]

Re: Dynex DX-LCD32, with no power

Effectively, at high frequencies, the cap is supposed to act as a short circuit, to filter out the higher frequencies, but if it doesn't have a low enough ESR, there is no where for this high frequency noise to go, other than to increase the output voltage.

Not really because the reference voltage for the ripple's peak-peak is the DC voltage anyway.
.

[wfdbackdraft]

Re: Dynex DX-LCD32, with no power

Ok. So what should I check next, or do I need to replace some capacitors?

[wfdbackdraft]

Re: Dynex DX-LCD32, with no power

Anyone?

[wfdbackdraft]

Re: Dynex DX-LCD32, with no power

Still sitting here with an open TV. Can someone help me out please? I'm ready to get this thing fixed.

Thank you!

[budm]

Re: Dynex DX-LCD32, with no power

Can you please take good clear pictures of the the whole chassis so we may be we will be able to see how it is wired up? We also need to see the third connector on the power supply board which I think it goes to the Inverter board, back side pictures of the power supply, closed up pictures of the inverter multi-pin connector, LCD panel make, model, revision number so we can look up the spec of the LCD panel which will show the T-CON and inveter board pin out of the connectors, etc.
By the way, do you get sound?, also try turning it on without the inverter board discoonected from the power supply board.

[wfdbackdraft]

Re: Dynex DX-LCD32, with no power

Thanks Bud. I'll get working on those pictures and specs tonight when I get home. I appreciate the help.

[budm]

Re: Dynex DX-LCD32, with no power

Looking at your picture of the power supply, I think this is what it has on it, see PDF. Right now the standby PS seems to be working (this power supply is running 24/7).

[wfdbackdraft]

Re: Dynex DX-LCD32, with no power

All of your assumptions are correct about where the wires are going. And I checked the voltage on the cap, and they fell right in line with where you said that it would.

[budm]

Re: Dynex DX-LCD32, with no power

So if I am right, right now you do not have the 24vdc feeding the Inverter board, yes/no? If not, disconnect the cable to the inverter board an see if the 24vdc comes back since if the 24vdc PS circuits sensing over current draw, it will go into shutdown mode.
Another reason you do have 23vdc can be due to 24vdc circuits itself, or it is not getting the command from the main board to turn it on.
Any voltage labels on the power supply connector at all? That will be a big help if they are labeled.