Westinghouse VR-4625 wont turn on

[jesselyons2002]

Got a lcd from a guy that was recycling a plasma and a lcd(The westinghouse) He told me they didn't turn on. So I took it to my house to figure out why. First thing. There were no lights whats so ever. So I open it up and took a look at the power board and other boards to see if there was anything bad I can see visually. Nothing.

Ok so I moved on to the powerboard to check to see if I was getting 120v at the plug. Sure was. Next I check to see If I got any power at the outputs. Nothing. After that I took the board out of the tv and checked the fuse. Fuse was bad. So for testing purpose. I replace the fuse with a single wire and put the board back in. Connected everything back and I got a front light to go on. Which was red. So I press the power button. Front light went from red to blue. But no screen. I checked the power board. Was getting 5v stand bye but no notice wasn't getting 24v for the inverter boards.


So what im asking. What do you think it could be ???

[Caleb]

Re: Westinghouse VR-4625 wont turn on

Mosfets, or output diodes are the common culprits on power boards. You can check with a multimeter in ohms mode. It could be many other things as well, you can try removing the harnesses and manually bringing up the power board by applying a 1k resistor between pson and your 5v standby. That should tell you if the fault lies in your power board for sure. bridging your fuse with wire is bound to cause more troubles than it fixes, you can use the light bulb trick for diagnosing shorted components in the primary.

[jesselyons2002]

Re: Westinghouse VR-4625 wont turn on

I shall try this. ^^^

[Agent24]

Re: Westinghouse VR-4625 wont turn on

Agree with Caleb, the light bulb is safer for testing than replacing fuse with wire... that said, if a shorted component took out the fuse it likely has already burnt out or it would have been obvious when you powered it up with wire instead of a fuse.

But you get *some* output so the primary side should be OK.

I assume the power button does not connect straight to the PSU. Check for a signal coming from the logic board to the PSU when you press the power button.

Carefully inspect the other PSU components for discoloration, burn marks, etc.

Post photos of the board if you can.

[jesselyons2002]

Re: Westinghouse VR-4625 wont turn on

Ok pictures up. Found a shorted mosfet(pointing at it with my pen). I replace it with another mosfet. But still getting no voltage at the 24 volt outputs for the inverter board

[tom66]

Re: Westinghouse VR-4625 wont turn on

You can't just replace a MOSFET with any old part. Thats like fixing a car with a flat by installing a random car tyre. Won't work. Ideally, the same part should be used. If not, you need to find the best match. Also, you need to replace the driver IC in some cases where the MOSFET has failed.
If the shorted MOSFET did not blow a fuse before, you're probably missing one somewhere.

[jesselyons2002]

Re: Westinghouse VR-4625 wont turn on

I look up the datasheets on both mosfets. Looks to me like they both match.I try to hook up a fuse the same as the old one.

[tom66]

Re: Westinghouse VR-4625 wont turn on

What specifications did you compare?

[jesselyons2002]

Re: Westinghouse VR-4625 wont turn on

For the mosfet or power supply board

[Agent24]

Re: Westinghouse VR-4625 wont turn on

For the mosfet or power supply board

For MOSFET - what specific characteristics? Switching speed? Current rating? On resistance?
Maybe post the model numbers of the old and the replacement here.

[jesselyons2002]

Re: Westinghouse VR-4625 wont turn on

replace one p16ne06. Old shorted one mdf18n50

[Agent24]

Re: Westinghouse VR-4625 wont turn on

replace one p16ne06. Old shorted one mdf18n50

Yeah I don't think that's going to work. I didn't look at the other parameters but the most obvious to me is that the MDF18N50 is rated for 500v Vds while the P16NE06 is only rated at 60v Vds.

That P16NE06 is probably already dead, if the PSU tried to startup at all.

[jesselyons2002]

Re: Westinghouse VR-4625 wont turn on

So I take that one out. Ok. Whoops.

[jesselyons2002]

Re: Westinghouse VR-4625 wont turn on

I put a fuse inline besides just the wire. Would a n channel mosfet with 600v range work. I got one of those.

[Agent24]

Re: Westinghouse VR-4625 wont turn on

600v should be OK but there will be some other parameters you need to check, like current rating, on resistance, gate voltage probably - I am not sure though. Post the part number of it, I'm sure tom66 will be able to confirm if it will work.

Found this online: "For DC MOSFET transistor applications, the important parameters to compare are the maximum voltage, maximum current, power, on-resistance, and gate-threshold voltage ratings." From (http://www.electro-tech-online.com/t...titute.122727/)

Oh and make sure you get the same package type - if the original is a plastic insulated one (from the datasheet it looks like your MDF18N50 is) and your replacement has a metal tab, you may have problems. Either insulate it with a mica washer or get a plastic case one.

[jesselyons2002]

Re: Westinghouse VR-4625 wont turn on

13a .33ohms k13a60d

[jesselyons2002]

Re: Westinghouse VR-4625 wont turn on

Those are the other specs

[Agent24]

Re: Westinghouse VR-4625 wont turn on

Lower current rating but will probably work just for testing, I guess.

[jesselyons2002]

Re: Westinghouse VR-4625 wont turn on

Yeah same thing with this mosfet. doesn't turn on

[Agent24]

Re: Westinghouse VR-4625 wont turn on

Problem likely lies elsewhere then. Did you check that the logic board is sending a power-up signal to the PSU?

Check the connectors going to the PSU, see if any have a change in voltage when you press the power button.