Barco LCN-42 No Power

[Jasgriff]

Re: Barco LCN-42 No Power

No good asking me - too "in depth". - ill leave that one for Budm. Can I just clarify what I was asking. Can you do a resistance check between J34 and R202 or pin 3 in case the trace where it goesunder J34 is damaged and has been soldered to J34.
Also did you visually trace R202 to pin 3 or did you ohm it -again in case it is broken under J34

J34 is 0.02 Ohms and R202 to Pin 3 is 0.2 Ohms. I tested it with the multimeter.

I also checked to see if J34 is connected to Pin 3 or R202 and it not linked at all.

[selldoor]

Re: Barco LCN-42 No Power

No good asking me - too "in depth". - ill leave that one for Budm. Can I just clarify what I was asking. Can you do a resistance check between J34 and R202 or pin 3 in case the trace where it goesunder J34 is damaged and has been soldered to J34.
Also did you visually trace R202 to pin 3 or did you ohm it -again in case it is broken under J34

[Jasgriff]

Re: Barco LCN-42 No Power

Right,

Tried it with no resistor and no mosfet. I still have 5v but now the 24v has gone off aswell as the 18v.

I have traced R202 back to the IC and it connects to pin number 3 which is the CS pin. I am guessing that because there is no voltage getting through that resistor that the IC would not run at all? Maybe causing the the mosfet to short?

I am getting roughly 5v where that blown resistor was so I am thinking of replacing that and then seeing If I can test to see what the IC is doing further.

Do we think that a 3k resistor will be ok to replace the blown one at r202?

[selldoor]

Re: Barco LCN-42 No Power

Hi - if you are clutching at straws can I throw in J34 again. Whilst you checked it back along the trace to check it was working, did you check that no solder had burnt through to the track it was jumping.Perhaps test from jumper to R202 - cant see where other end goes - does it reach IC201? ( I see in later pics J34 has been cleaned up.)

You also mention thermal paste early on. Did you think B8? had been replaced using thermal paste? and if sodoes it also need an isolation strip and has it got one?

Talking of soldering being cleaned up there is one pin that looks worse - see pic might be worth checking that it is not connecting across to the parallel trace.

[Jasgriff]

Re: Barco LCN-42 No Power

Will I need to replace the resistor or can I leave that out too?

[budm]

Re: Barco LCN-42 No Power

I think what we can do is to leave out the MOSFET, since we are still getting the VCC to the SMPS that drive that blown MOSFET, then we see why we are not getting the Gate drive output from that IC.

[Jasgriff]

Re: Barco LCN-42 No Power

I have another Resistor and mosfet but i'm thinking that it will just blow again?

Yeah its very strange.

Right Can you see the R202 resistor. If that was blown would that cause the Mosfet to overload somehow?

[budm]

Re: Barco LCN-42 No Power

Since the SMPS IC was not running (there was no 18vdc on the output side) and no drive to the Gate of the MOSFET, then I do not see why the MOSFET will just conduct by itself. That is strange.

[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.

[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

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 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

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

[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

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

So the bridge check OK?

[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

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

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

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.