Barco LCN-42 No Power

[budm]

Re: Barco LCN-42 No Power

Get 10watts if you can just want to start with lighter load first.

[Jasgriff]

Re: Barco LCN-42 No Power

Ok cheers Budm.

I have ordered some 1 pin connectors and some 24v 20 watt bulbs to make up some leads for adding load to some of the pins when the 24v circuit is back up and running.

[budm]

Re: Barco LCN-42 No Power

Ok that is OK. I will look at the latest picture tonight to see what is going on.

[Jasgriff]

Re: Barco LCN-42 No Power

The Zener on its own is 511 Ohms with the Negative probe on the black strip and 11.9K when I reverse the probes.

Just re checked everything on that pin 6 and its connected to j33 and c207.

[budm]

Re: Barco LCN-42 No Power

I beleive the SMPS IC for the 24dc power supply section is on that board, but let me verify the traces for sure that the VCC is generated fromm that board first, by thw way, how about that 18 Ohms reading on that ZENER, is it really 18 Ohms when you measure across that ZENER?

[Jasgriff]

Re: Barco LCN-42 No Power

Do you think I am going to need to de-solder that secondary board to see what's going on underneath it?

I have found the part numbers of the 2 transistors that the 8.53v's comes from.

A1020 & C2655

[Jasgriff]

Re: Barco LCN-42 No Power

I have replaced the resistor and nothing went bang.

I retested the voltage on the pin that you asked and its 8.53v thin 6.2v on pin 6 VCC.

Do you think this smps was also controlling the 24v supply?

[budm]

Re: Barco LCN-42 No Power

It looks like the VCC is generated from that sub circuits board with multi pins, not sure yet.

[Jasgriff]

Re: Barco LCN-42 No Power

Here is the picture without the markings.

Yeah I managed to get my proper camera back. Makes a big difference taking pictures in the day light too.

[budm]

Re: Barco LCN-42 No Power

Do you mean you read 12 Ohms across that Zener diode both ways (reverse the test probes)? By the way, the Cathode side (Black) end should be connected to pin6, the Anode end should be connected to Ground.

[budm]

Re: Barco LCN-42 No Power

Can you please send me the same picture without the marking? by the way , you are getting good at taking the pictures.

[Jasgriff]

Re: Barco LCN-42 No Power

By the way that trace should go directly to the VCC pin of the SMPC IC you had replaced, please verify that for me, an at the Vcc pin, there is a ZENER diode connected to it also, ZD201.

Yes that test point goes back to VCC on Pin 6 and it goes through the zener diode. It tested at about 12 Ohms between the test point and the VCC pin.

[Jasgriff]

Re: Barco LCN-42 No Power

Here is the trace it goes back to two transistors.

[budm]

Re: Barco LCN-42 No Power

By the way that trace should go directly to the VCC pin of the SMPC IC you had replaced, please verify that for me, an at the Vcc pin, there is a ZENER diode connected to it also, ZD201.

[Jasgriff]

Re: Barco LCN-42 No Power

Thats was a typo sorry. I was thinking of 12v because I was tracing the cables yesterday and the 24v cables split off into pairs. So I was thinking 12v. Its definately 24v. I will have a look to see where that power comes from now.

[budm]

Re: Barco LCN-42 No Power

We should have about 13vdc at those two points instead of 8.53, we were getting the 13v after you replaced the MOSTFET and the SAMPS FOR THE 18VDC power supply section. This low voltage of 8.53vdc may explain why the 24vdc power supply stops working. We need to trace that trace out teo see where it goes to.
By the way, your power supply only has 24vdc, 18vdc and 5vdc outputs. Which 12vdc out put are you referring to?

[Jasgriff]

Re: Barco LCN-42 No Power

Ok going to have a little look at these voltages....

330V across the big cap with the 5v jumper on.

330v across the big cap without the 5v jumper in place.

8.53v on those test points on your picture. It seems to be creeping up slightly every couple of seconds.

I have no 12v with PS_ON applied.

I am thinking of soldering another resistor in but leaving out the mosfet to see if that brings back the 12v supply.

[budm]

Re: Barco LCN-42 No Power

So are you still getting the VCC at pin 6? R202 is the current sensing the voltage drop on the Source resistor of the MOSFET, if voltage drop on the Source resistor is too high due to too much current draw by the MOSFET, it will shutdown the output of the SMPS IC.
I think we need to get the 24vdc running again first, you have no 24vdc with the PS_ON applied, right?
Please see the PDF, if you do not have that voltage, then it may explain why the 24vdc PS is dead also.
By the way, do you remember the DC reading on the main cap without PS_ON and with PS_ON applied?

[Jasgriff]

Re: Barco LCN-42 No Power

Put your Fluke 177 in capacitance mode and measure the big cap in circuit. I have measured it this way a few times and almost every big cap filter will read a bit low compared to its rating.

I took it out and measured it. It measured a little lower but I later realised that a fuse had also blown in the plug so I changed that and put the cap back in.

Now without the mosfet in im still getting 330v on the big cap.

[retiredcaps]

Re: Barco LCN-42 No Power

I am now wondering if the filter cap has blown?

Put your Fluke 177 in capacitance mode and measure the big cap in circuit. I have measured it this way a few times and almost every big cap filter will read a bit low compared to its rating.