Barco LCN-42 No Power

[Jasgriff]

Re: Barco LCN-42 No Power

SMPS have arrived. Hopefully I will have them in my possession tomorrow night. Then we can see whats going on

Also just won 2 more monitors to play about with which I should have in a couple of days.

[budm]

Re: Barco LCN-42 No Power

The suspense is killing me!

[Jasgriff]

Re: Barco LCN-42 No Power

Right got the bits before I fit the transistors.....

Q201 = npn
Q202 = pnp

I recall it being the other way around so I thought I would check

[Jasgriff]

Re: Barco LCN-42 No Power

Right Parts fitted!

I first turned it on for a short period of time and could hear a slight noise.

Not sure if it was anything to worry about I turned it off and then tested the fuse etc to see if it had tripped again and it hadnt.

I powered it back up and the 24v rail seems fine but the 18v one has no power. I also tried the 5v rail and this was just over 5v and steady.

Does this mean the new smps ic and the transistors have worked because I now have power to those rails or was that smps looking after the 18v rail and thats why its not working?

[Jasgriff]

Re: Barco LCN-42 No Power

Noticed something else...

GT1 + GT2 which are near the main fuse flash when I turn the power on. They look like Zener Diodes im guessing they are not supposed to flash?

[budm]

Re: Barco LCN-42 No Power

I think they are Gas Discharge tubes for surge protection (I do not see then on the top view of the power supply board picture), they should not flash (Conduct)unless there are surges, they should be rated at about 400v or more.
Can I see the pictures?
Well, the circuits are still not working. We replaced the damaged parts for the 18VDC power supply. We need to see if we have Vcc the SMPS IC you just installed, also recheck your soldering works just incase, right now the middle pin (Drain) of the new MOSFEt should have DC voltage on it, can you verify that?

[Jasgriff]

Re: Barco LCN-42 No Power

You cannot see the gas discharge components as they are just hidden in this picture.

See the big grey component on C1 I think this is where the noise is coming from.

I will take a proper picture of where the flashes are coming from and I will check that the SMPS ic has power and the Mosfet that I changed.

Apparently I have to watch a film now so I will try and do that once its finished.

[Jasgriff]

Re: Barco LCN-42 No Power

Ok checked the VCC of the SMPS IC and it is showing 13.4v. This seems to be right. I will check the Mosfet now.

Ok 390v On the mosfet I have included a pic of the whole bottom of the board and how I measured it.

[budm]

Re: Barco LCN-42 No Power

Can you take a reading of R207 one end is connected to the transfomer pin6, it is close to the IC SMPS you just replace? We have everything but it is not driving the gate of the MOSTFET.
Also set the volt meter to AC at about 20VAC scale AND CHECK PIN 5 to see if anything is coming out of that IC.

[Jasgriff]

Re: Barco LCN-42 No Power

Oh dear heard something click and smelt something burning. Turned it off and checked the fuse. The fuse was fine.

Plugged it back in and now im not getting anything on the big cap.

[budm]

Re: Barco LCN-42 No Power

Oh man! there should be something on the main filter cap unless the bridge is blown or the main fuse is blown. See if you do have AC at the bridge AC in.

[Jasgriff]

Re: Barco LCN-42 No Power

Got AC power going into the bridge rectifier but no DC coming out of it. Im guessing that where the smell came from.

[budm]

Re: Barco LCN-42 No Power

So the bridge check OK?

[Jasgriff]

Re: Barco LCN-42 No Power

Na the bridge has AC going in but no DC coming out.

ts15p06g Thats the model I will have to get one ordered tomorrow. I am guessing thats what was making the noise earlier so it wont hurt to change it.

[budm]

Re: Barco LCN-42 No Power

That is strange that the Bridge decide to quit on you. By the way, during all this testing, the board is connected to the rest of the boards right, it does not like running without the loads. If you are going to do stand alone then I would use lamps for load.

[Jasgriff]

Re: Barco LCN-42 No Power

I had it all wired up to start with but I disconnected it all to test the ic on the bottom. I am thinking that the bridge rectifier was the bit making the noise which happened even underload so hopefully it was on its way out anyway. Its a powerfully recifier 800v 15A

[Jasgriff]

Re: Barco LCN-42 No Power

Right I'm trying to source a replacement recifier.

The one that's in it is a Glass Passivated Recifier and the case is a TS-6P.

This style of case seems to be very uncommon and I'm not sure if I have to use another Glass Passivated one?

This is the nearest one I can find I am sure that will do.

http://www.farnell.com/datasheets/58654.pdf

[Jasgriff]

Re: Barco LCN-42 No Power

Ordered a couple of rectifiers. I am pretty sure they will be ok and they are coming from Farnell in the UK so with a bit of luck they will be here within a couple of days. I am really hoping that when fitted it makes no noise and then I can continue to try and get the 18V side of things up and running.

[Jasgriff]

Re: Barco LCN-42 No Power

Right fitted a new recifier and tested again. I am getting AC on the middle pins but nothing out of the DC pins so there is nothing going to the big filter cap. I am now wondering if the filter cap has blown?

What else can I check to find out why I am getting no DC?

[Jasgriff]

Re: Barco LCN-42 No Power

Right took the cap out then put it back in and tested again.

The cable that I used to power the set blew the 5A fuse in the plug so I swapped that for a 12A fuse and tried again and it blew the resistor again?

Right checked the Mosfet that blew the first time and its blown again. The other components look to be ok this time just the resistor and the mosfet so there must be something else thats causing the mosfet to blow.