GNR TS700 2 seconds to black

[budm]

Re: GNR TS700 2 seconds to black

I have repaired many Dell and ACER with these bad tuning caps used in the Royer oscillator setup in the inverter output circuits, most of the new monitors do not use the Royer Osc any more.

[retiredcaps]

Re: GNR TS700 2 seconds to black

Tuning caps arrived today and new Transistors.

Hmm, this is the first case that I can remember that the tuning caps are at fault.

I certianly would have NOT figured this one out.

[Jasgriff]

Re: GNR TS700 2 seconds to black

But once its fixed it will be even more satisfying!

Only got to get the 18v line up and running then it will become easier.

I am off next week so I will have lots of time to look at it.

[budm]

Re: GNR TS700 2 seconds to black

That BARCO is a tough one.

[Jasgriff]

Re: GNR TS700 2 seconds to black

No Probs,

Another lesson learnt there!

It's not all good news though unfortunately as I have now ran out of things to fix! Well apart from the Barco.

[budm]

Re: GNR TS700 2 seconds to black

Great, thanks for the good news.

[Jasgriff]

Re: GNR TS700 2 seconds to black

Tuning caps arrived today and new Transistors.

All cleaned up and then fitted. Just tried it for an hour and its working fine.

Cheers for the tip Budm...

[Jasgriff]

Re: GNR TS700 2 seconds to black

Ordered some new tuning caps and transistors for this one. Looks like i'm going to spend more more money on this than its worth but im keen to get it up and running. Bit should be here tomorrow so I will keep you posted.

[budm]

Re: GNR TS700 2 seconds to black

That will be good way to go. I always test those tuning caps, a must, when I work on the inverter section. Resistance reading should be infinite since cap is an open circuit device. If the meter which runs on 9V batteries can show the resistance reading, just imagine what happen when the cap is exposed to a couple hundred volts of pulses.

[Jasgriff]

Re: GNR TS700 2 seconds to black

The one that doesnt work goes out of range.

I have attached a couple of pics of the working one measure for capacitance and resistance. I would imagine swapping them both at the same time would make sense.

[budm]

Re: GNR TS700 2 seconds to black

They are 0.22uF 5% (224J), at least 250v rating.
One is reading 340nF (.34uF)? It does not have any resistance reading on this one?
If they are not within 5% (J) then you do have problem and that can damage your new MOSFETs

[Jasgriff]

Re: GNR TS700 2 seconds to black

Right took them out to measure them.

1 measures out of range and the other measure 340nf.

7C224J is the model of the cap.

I am guessing this is what could be causing the short?

[budm]

Re: GNR TS700 2 seconds to black

The two blue caps in the top center of the picture. If they are off value then that will cause the Osc to run at the wrong frequency as designed and can cause the MOSFET to over heat or damaged.

[Jasgriff]

Re: GNR TS700 2 seconds to black

Il get the pic now.

[budm]

Re: GNR TS700 2 seconds to black

There should be a cap connected in parallel with the primary side of the inverter transformer. Do you have the picture of the top side of the board?

[Jasgriff]

Re: GNR TS700 2 seconds to black

Desoldered the Diodes and they tested ok outside of the circuit. I desoldered the mosfets too and 1 of them seems ok whilst the other is shorted.

are the tuning caps the ones that are connected directly to the mosfets?

[budm]

Re: GNR TS700 2 seconds to black

Did you check the tuning caps? there should be caps on the top side of the board for this Royer Oscillator circuits.

[retiredcaps]

Re: GNR TS700 2 seconds to black

There are 2 diodes connected to these mosfets and the diode on the broken ones appears to be shorted. I am guessing this is what is breaking the mosfets?

Probably. Desolder the diode and verify out of circuit that it is shorted.

[Jasgriff]

Re: GNR TS700 2 seconds to black

Right the new mosfets don't test shorted but the working old ones that I moved to replace the broken ones are now shorted. nooooooooo another couple of wasted mosfets!

There are 2 diodes connected to these mosfets and the diode on the broken ones appears to be shorted. I am guessing this is what is breaking the mosfets?

I will get some pics in a bit.

[retiredcaps]

Re: GNR TS700 2 seconds to black

1) Do the new mosfets test shorted?

2) Do the pins get any DC power?

3) Please post a picture of the top side of the power board.