Barco LCN-42 No Power

[budm]

Re: Barco LCN-42 No Power

That is why I built a fume extractor after 35 years of sucking up the solder fumes, I use the bath room venting fan and got the charcoal filter and a light dimmer for controlling the speed. Ah, there is nothing like the smell of solder fume in the morning!
Oh, where was it again?
I sure like to know who generated this darn VCC.
I will have to look at NCP1377 data sheet again to remember what it is for.
Good job for finding the short, Jasgriff.
Oh by the way, you put that jumper back in place that I had you remove to find out why we lost the VCC? I would also leave the MOSFET out this time. And the two transistors and resistors you replaced are still good?
That pin 8 is the kick start pin, so I would think some kind of power connection should be there to kick start it.

[Jasgriff]

Re: Barco LCN-42 No Power

Retired caps,

Can you put a circle around where you think pin 8 is connected please I can't see which resistor you mean.

Budm,

I only found the short after you removing jumpers like you suggested that helped me pin point the problem. The problem yesterday was I had a few hours of messing about with it before you guys were even out of bed so I have already put the mosfet back in as I was too excited. I will take it back out though whilst I find the source of the hv pin.

I have come home to my mums for the weekend so I'm not going to be able to access the etc for a few days. I have still managed to find myself things to fix though! My central locking wasn't opening the boot of my car so I fixed that and my old dear had a Philips 26 inch TV with a permanent red line down it so far I have fixed them both :-)

[retiredcaps]

Re: Barco LCN-42 No Power

Retired caps,

Can you put a circle around where you think pin 8 is connected please I can't see which resistor you mean.

I'm looking at the datasheet which recommends using a resistor in series. I have found that the "typical application" listed in the datasheet is a good proxy for the real board. However, that is not always the case.

If pin 8 (HV) has continuity to the positive leg of the large capacitor, then there is no resistor. If pin 8 has no continuity, then that suggests there is a resistor in series.

The most likely candidates for this resistor in series with pin 8 (HV) would be on the front side. Mabye R4, R5, R110, R112. Unless there is a SMD resistor on the backside that says 683?

PS. Regulars will know I'm still weak at reading schematics so I could also be way off?

[Jasgriff]

Re: Barco LCN-42 No Power

when I get home I will have another look. I just remember looking at that pin when there was no chip there thinking why is the hv pin not connected.

[retiredcaps]

Re: Barco LCN-42 No Power

when I get home I will have another look. I just remember looking at that pin when there was no chip there thinking why is the hv pin not connected.

Hmm, I had another look once I got multiple windows open and every photo rotated properly. It is a long way from pin 8 to those top side resistors I mentioned earlier.

What is covered underneath the glue around the J43 area?

[retiredcaps]

Re: Barco LCN-42 No Power

And I see R206 in that same area, but the angle of the picture blocks the color band.

[Jasgriff]

Re: Barco LCN-42 No Power

Right,

I decided to take the IC off again and this time it removed pad 8.

I have taken away the top coat to try and see exactly where Pin 8 connected to and it looks like it was not connected in any way?

So it looks like pin 7 and pin 8 were not used at all.

[BigDaddyAdy]

Re: Barco LCN-42 No Power

Hello guys,

I know it's an old thread, but here is my story:

I have two barco's with the same defect:
No 18V output.

I found that mosfet 11n80c3 burnt, the 18ohm power resistor exploded, the 2 33ohm resistors r203 and r204 burnt, r202(100ohm) burnt.

I replaced the mosfet with 11n60c3 (i have lots of them), the 18ohm replaced with 22ohm, r203, r204 eith 33ohm, r202 on one board with 180ohm, on the other with 100ohm.

Ok, now i have one working board, and one not.
On the working board is the 180ohm resistor and i also replaced ic 201, although it apeared to be good.

Now, on the other board i replaced r202 with 100ohm but haven't replaced ic201. First time i tested the board everything was fine, the power board was working well. After i mounted the board on the rack, on power on it blew again (the mosfet, r202, r203, r204) i thought because i put a 0.25w resistor on r202. Replaced again everything, this time a 0.5w 100ohm resistor, tested, it worked. Mounted on the chassis, it worked, turned it off and back on, it worked, turned it off and back on, it blew again. This time it also blew the 2 smd transistors q201 and q202 and r202 survived.

Now i am thinking of replacing the ic (maybe that is the culprit).

Can anyone help me with those two transistors?
Will these FMMT493 and 593 work?