Rapid flashing screen Vistron LCD TV - PSU or Inverter or?

[davcom1]

Re: Rapid flashing screen Vistron LCD TV - PSU or Inverter or?

Thanks to everyone for your help and advice with this - much appreciated.

I've now ordered a Rubycon cap to replace the Lelon.

David

[selldoor]

Re: Rapid flashing screen Vistron LCD TV - PSU or Inverter or?

Does the jumper wire need to be particularly large in diameter? At present, I've used wire comparible to the other existing wire jumpers as per my image on post #23

Should be ok trace is only thin even if wide. If you can get at it when the tv is on check to see if you can see it overheating - BUT remember dont touch it until the big caps has discharged. Invest in a good name cap as Tom says.

[tom66]

Re: Rapid flashing screen Vistron LCD TV - PSU or Inverter or?

Replace the cap with a decent quality one - it will only fail again like the Samxon.

[davcom1]

Re: Rapid flashing screen Vistron LCD TV - PSU or Inverter or?

Thanks budm and selldoor.

I hadn't read the dim bulb idea before I put the main capacitor back in place and soldered in a wire to jump the damaged trace.

Plugged in and switched on and the TV works again... (!!)

Does the jumper wire need to be particularly large in diameter? At present, I've used wire comparible to the other existing wire jumpers as per my image on post #23

I also remembered to give the soldered areas a good clean off this time too as I'm pretty sure it was excess flux that did the damage.

Regards,

David

[selldoor]

Re: Rapid flashing screen Vistron LCD TV - PSU or Inverter or?

To save big blow-outs you could rig something like this
antiqueradio.org/dimbulb.htm

[budm]

Re: Rapid flashing screen Vistron LCD TV - PSU or Inverter or?

You need to use jumper wire to fix that blown trace. Since the MOSFET check open, I still would like you to look at the body of the MOSFET to make sure there is no sign of damage on the body, it could have blown so bad that it went open circuits. For the copper trace to blow and took out 5A fuse, something shorted badly to cause that kind of damage.

[davcom1]

Re: Rapid flashing screen Vistron LCD TV - PSU or Inverter or?

Hi all,

Thanks for the advice so far but now I'm at a loss as to what to do next?

I tested the other MOSFETs on the board and they all had similar readings. Do I just put it all back together, replace the 5A fuse in the plug and repair the PCB trace and hope for the best?

I still have the option of a replacement board if it all goes bang again!

[davcom1]

Re: Rapid flashing screen Vistron LCD TV - PSU or Inverter or?

selldoor - sorry, I did check the resistance as per the image from budm and posted it (#25)

It read as an open circuit. Am guessing the cap removed makes no difference to this.

[davcom1]

Re: Rapid flashing screen Vistron LCD TV - PSU or Inverter or?

Getting called away for an hour now by the other 'arf as she wants to go shopping... doh!

Have quickly done a diode check across the large one close to where the pop happened and it had a reading of 450?

[selldoor]

Re: Rapid flashing screen Vistron LCD TV - PSU or Inverter or?

No - see edit - Budm has marked out the traces so if it needs wires to mend the traces we can see where they should go. Do Budms resistance check and post result

[davcom1]

Re: Rapid flashing screen Vistron LCD TV - PSU or Inverter or?

selldoor - the fuse has not blown at the power input. Do you still want another pic of the damaged area?

Part no of board is GPAC 211424A rev 2.1

[davcom1]

Re: Rapid flashing screen Vistron LCD TV - PSU or Inverter or?

budm - tested as per your pic and is reading open circuit. I get a resistance of 8.36 at 20k setting between the vertical upper and lower leg of what I guess is the MOSFET.

[selldoor]

Re: Rapid flashing screen Vistron LCD TV - PSU or Inverter or?

It does look repairable, its around now I wished I'd made my usual request for pictures
of both sides of the boards early on. What is the part number of the board ?
Clean up the area with some isopropyl alcohol and take another close up of the damage zone. Just by the mains socket on the board is a black encased fuse - can you check it.


Dont need another pic - Budm has marked the traces out.

[davcom1]

Re: Rapid flashing screen Vistron LCD TV - PSU or Inverter or?

Ok, have removed the cap and tested as best I can... connected to DMM at 2000k ohms setting and resistance rises. Then tested voltage across terminals after 30 seconds or so and it read 0.2V

Photo attached shows top of board where cap was located. No obvious signs of damage here.

Did notice a tell tale "sizzle" as I de-soldered suggesting I had left flux on the terminals.

[tom66]

Re: Rapid flashing screen Vistron LCD TV - PSU or Inverter or?

If you used a poor quality primary cap and it failed it would damage the PFC stage (MOSFET, diode and cap at a minimum usually.)

[budm]

Re: Rapid flashing screen Vistron LCD TV - PSU or Inverter or?

Please the PIX.

[selldoor]

Re: Rapid flashing screen Vistron LCD TV - PSU or Inverter or?

No dont short the Big cap - test it with a meter on DC 600 to see if it holds any voltage. If less than 20 test again with meter on 20 . If less than 5 then short it out with a resistor or a light bulb.
If you can take it off the board post a picture of what is under it - looks like it was the right way round when it is discharged test it to see if it is shorted.
Looks like there are some links under there id like to see tha damage to the top of the board.

[davcom1]

Re: Rapid flashing screen Vistron LCD TV - PSU or Inverter or?

Ok, that's a good point. I didn't use loads of flux but didn't clean up very thoroughly either.

So effectively, the board heats up as it is working and then liquifies the residual flux which then runs and causes a short?

Would that be enough to cause the scorching and blow a section of the PCB away?

Silly question but, is it safe to short across the main capacitor (now removed from the mains of course) to make sure I don't get a jolt?

budm - thanks for the input although once it gets to MOSFET, I'm lost, sorry!

[budm]

Re: Rapid flashing screen Vistron LCD TV - PSU or Inverter or?

That the blown ground trace which is part of the Source pin high current ground return, I think yOUR MOSFET is shorted.

[vinceroger69]

Re: Rapid flashing screen Vistron LCD TV - PSU or Inverter or?

could there of been a lot of flux from your solder on to the new capacitor joints maybe worth cleaning the area up on the back of the board with some cleaner to remove the flux if there is any as it could of shorted out as above the left arrow it looks like a spark has arked across 2 points?