Barco LCN-42 No Power

[retiredcaps]

Re: Barco LCN-42 No Power

I am not sure what the AC frequency bandwidth of your 175 is.

45Hz to 500Hz for 600mV to 600V according to manual page 12. For range 1000V it is 500Hz to 1kHz.

Not as wide as your Fluke 87 which goes from 50Hz to 20kHz.

[budm]

Re: Barco LCN-42 No Power

That is too low, that why I keep my 87 for poor man scope (I do have 4 scopes).

[Jasgriff]

Re: Barco LCN-42 No Power

I thought retiredcaps would get to the answer quicker than me. I bet you didnt even have to look it up!

Here is the setting that I would have though was right.

[budm]

Re: Barco LCN-42 No Power

You meter AC frequency bandwidth is too lo for it to measure any AC in the 30~50KHz range.

[retiredcaps]

Re: Barco LCN-42 No Power

You meter AC frequency bandwidth is too lo for it to measure any AC in the 30~50KHz range.

I think I saw a Uni-T multimeter in one of Jasgriff's pictures as well. If correct, does that Uni-T have a bar graph?

[Jasgriff]

Re: Barco LCN-42 No Power

The UNI-T one is a cheap one. I think it has probes and an on off switch and that's about it

[Jasgriff]

Re: Barco LCN-42 No Power

Just done a little more testing to try and work out whats going on.

It seems when I turn it on some power is supplied to the mosfet that I have marked with the letter A. This starts off at 75v or so but then quickly drops down to nothing. The same happened to the transistor which I think might be driving it? That transistor starts off at just short of 6v but then slowly drops down under 1 vault.

[budm]

Re: Barco LCN-42 No Power

I would like to try this to see if the 18v power supply section is loading down the 13VCC LINE, there is jumper wire in the middle of the picture shown with red line, lift one end up and see if the 13vdc comes back.

[retiredcaps]

Re: Barco LCN-42 No Power

The UNI-T one is a cheap one.

Geez, 250V AC is barely enough to meet 220-240V AC regions.

And there is no way it can measure the PFC DC voltage of any modern electronic device with a limit of 250V DC.

[Jasgriff]

Re: Barco LCN-42 No Power

I would like to try this to see if the 18v power supply section is loading down the 13VCC LINE, there is jumper wire in the middle of the picture shown with red line, lift one end up and see if the 13vdc comes back.

I will try it now.

[Jasgriff]

Re: Barco LCN-42 No Power

Geez, 250V AC is barely enough to meet 220-240V AC regions.

And there is no way it can measure the PFC DC voltage of any modern electronic device with a limit of 250V DC.

At the moment it cant read anything as I blew the fuse by touching the wrong connection

[Jasgriff]

Re: Barco LCN-42 No Power

I would like to try this to see if the 18v power supply section is loading down the 13VCC LINE, there is jumper wire in the middle of the picture shown with red line, lift one end up and see if the 13vdc comes back.

Its done the opposite.

I have disconnected the left hand side of the jumper and now I have 0v on the left hand track that goes back to the sub board but 6.2v on the right hand side that leads back to the replaced chip?

Maybe the vcc comes from somewhere else and that feeds back up to the sub board?

[Jasgriff]

Re: Barco LCN-42 No Power

I have attached a pic to show the jumper that I removed and the black line shows where the vcc is coming from im getting about 8v over the black line.

If you can see C304 at the bottom there is 12v there so it seems that this is where the 13v should be coming from.

[budm]

Re: Barco LCN-42 No Power

Boy that is strange, you may be right that the VCC is coming from somewhere else. It is usually generated by the winding of the always on power supply then it will be fed to switched transistor to be turn on when it receives the PS_ON signal.
Right now we know that the 18v, 24v are not working so it can not be generated by those two transformer. You may have to trace the line, it should end at the Cathode of the Diode and DC filter cap some where.

[Jasgriff]

Re: Barco LCN-42 No Power

Right trying to trace back where this 13v should be coming from. I cannot work out from the number what IC3 is or what it does. There doesn't seem to be any significant voltage going into it to give 12.55v out on the marked pin?

Does anybody know what it is so I can continue to trace?

[Jasgriff]

Re: Barco LCN-42 No Power

Right,

I found out what it was!

The new IC that I replaced became shorted on the DRV pin and the VCC pin one I disconnected that part of the circuit I get 14 volts back and then the 24v line was up and running!

I have now replaced the IC but left out the mosfet so I am going to test the IC to see what voltages I have going across it then I might throw in another mosfet to see how we get on.

P.s I have replaced the CS resistor that was previously blown. I am thinking that did not help with the operation of the IC and I am really hoping that by replacing that the IC will do its job and drive the mosfet.

[Jasgriff]

Re: Barco LCN-42 No Power

New IC fitted and Mosfet back in.

I am getting just short of 14v on the VCC pin now but nothing on DRV.

I also noticed that there is less than 0.5V on the HV line? I am sure that this isnt correct according to the Datasheet.

[retiredcaps]

Re: Barco LCN-42 No Power

I also noticed that there is less than 0.5V on the HV line?

Is the resistor that is in series with HV pin 8 open? According to page 12 of the NCP1377 datasheet, it is typically a 6.8k/0.5W resistor.

[Jasgriff]

Re: Barco LCN-42 No Power

I am struggling to find where the HIV pin is attached too. I remember when I took the chip off it looked like it wasn't connected to anywhere. Do you think looking at the diagram that it definitely should be connected up?

[retiredcaps]

Re: Barco LCN-42 No Power

I am struggling to find where the HIV pin is attached too. I remember when I took the chip off it looked like it wasn't connected to anywhere. Do you think looking at the diagram that it definitely should be connected up?

Well, I wrote the post after desoldering a single capacitor so I could be high on solder fumes because I didn't use a fan for one capacitor, but figure 1 on page 2, shows a resistor in series with pin 8. That resistor looks like it is connected to the positive leg of the big filter capacitor.

If you can't find a resistor, then you should have direct continuity from the HV pin to the large capacitor then.

Note to self. Always use the fan regardless how long I'm soldering.