Barco LCN-42 No Power

[Jasgriff]

Re: Barco LCN-42 No Power

Yeah I did the same yesterday and all it did was came up with flights im thinking that is a date stamp hopefully and the first set of letters and numbers are the model. When I searched using the model from that Vizio link I came up with better results.

[mcdaydavies]

Re: Barco LCN-42 No Power

Lots of the solder joints look cold, I would go and check over them.

[Jasgriff]

Re: Barco LCN-42 No Power

On the mainboard or the sub board?

[budm]

Re: Barco LCN-42 No Power

Hmm, I wonder what the Dual-OP Amp is used for on your board and in the Vizio.

[mcdaydavies]

Re: Barco LCN-42 No Power

Under the psu, the solder joints have got a "circle" and looks like they may have cracked. Circled in yellow.

[Jasgriff]

Re: Barco LCN-42 No Power

Not sure I will ohm out the middle 'Dual-OP' chips if it is that and let you know where the pins go.

[Jasgriff]

Re: Barco LCN-42 No Power

Just sat here looking at this board for 10 minutes looking at whats going on I am going to put that sub board back in and take some more measurements so we can see what's going in and coming out of those sub board pins.

[Jasgriff]

Re: Barco LCN-42 No Power

Here are some readings that I have taken from the board powered up.

R2B, R2A, R3B and R3A are all connected to the + side of the bridge rectifier Via a jumper. I have attached a better pic of those resistors to see if the values represent what is actually coming out of them.

[Jasgriff]

Re: Barco LCN-42 No Power

I replaced the blown mosfet on this today and the blown SMD resistor that connected to the CS pin of the SMPS IC. The great news is that it didnt blow this time.

[budm]

Re: Barco LCN-42 No Power

The PFC boosted voltage is also fed another resistor network. Did you get the 13vdc back that was treading low on the SMPS IC Vcc pin?
By the way, what do you to make the marking on the pictures on post #148, I like to use that instead of using the PDF.

[Jasgriff]

Re: Barco LCN-42 No Power

No still not getting 13vdc. Im getting about 2.5v out of the ic to the gate of the mosfet that previously blew. I am going to get a few more readings off it in a minute to give you an idea od what voltage is where e.g at the end of that resistor network.

I use paint to make markings on pictures. I find it best to zoom in to make your markings this makes them clearer when you save them.

[budm]

Re: Barco LCN-42 No Power

Becareful if you are getting 2.5vdc steady to the Gate, that will turn on (slightly) the MOSFET, the MOSFET and the transformer will not like that since it supposes to be pulsing the Gate. I still cannot figure where that 13 v is generated from, and right now the PFC Voltage boost is proably not working either. By the way, did you check the MOSFET'S and Diode in the PFC section to see if they are OK?

[Jasgriff]

Re: Barco LCN-42 No Power

Do you think its worth taking the mosfet back out again for now?

How can I tell if that 2.5v is pulsing or not?

do you mean the diodes on the sub board?

[Jasgriff]

Re: Barco LCN-42 No Power

Right managed to move a few monitors that were fixed so that they are now out of the way for me to focus on my outstanding jobs so thought I would crack on with this one first....

I have removed the mosfet so that there is no power at all getting through to the transformer to cause more damage.

I have also replaced the 2 bad caps up on the top left. I knew they wouldn't make any difference to the problems I have at the moment but I though I might as well get them done. The ones that I took out were well goosed.

I am just going to double check that the voltages I had last time are still there just in case they did make a difference.

[budm]

Re: Barco LCN-42 No Power

I would leave the MOSFET out, you have to use the scope to look for the Gate drive signal.

[Jasgriff]

Re: Barco LCN-42 No Power

What scope lol.

am I going to need to buy an oscilloscope?

[budm]

Re: Barco LCN-42 No Power

Yes, an OSCILLOSCOPE. Do you have Fluke meter with bar grahp display?

[retiredcaps]

Re: Barco LCN-42 No Power

He has a Fluke 175. It is True RMS and has an analog bar graph.

[Jasgriff]

Re: Barco LCN-42 No Power

I will have a read on the net to see how I can scope the signal with this Fluke.

[budm]

Re: Barco LCN-42 No Power

You just put it on AC mode and you should see the Graph bar moving up and down. You can try that on a known working SMPS IC out put pin. I am not sure what the AC frequency bandwidth of your 175 is.