Tv Inverter works without Output caps but why?

[reessi]

On the following PSU/Invert board -> 17IPS02-2

The fault is that the tv backlights do not turn on, there are 4 backlights, wired in pairs together. Each pair has a ceramic cap across the outputs. I have a small diy meter off ebay that can recognise components, it didn't recognise them. My multimeter said they were open circuit. After removal the backlights work so I bought new ones which the diy meter correctly reads. But the backlights do not work when I put them in circuit


So I would like to know can I just leave them out as the tv now works?
But I would like to know what they are there for and why the lights will not work with the new ones? Are the lights failing and this could cause this to happen?

Many thanks- Simon.

[chrismurphy]

Re: Tv Inverter works without Output caps but why?

simple answer NO

[dick_barton]

Re: Tv Inverter works without Output caps but why?

Do you have photo's of what you removed and what you replaced them with showing their markings.

[ReeceyBurger123]

Re: Tv Inverter works without Output caps but why?

Dont run it ! The caps are used to stabilise the ripple on the input of the fets with out them the fets will blow shortly !

[CapLeaker]

Re: Tv Inverter works without Output caps but why?

Just think man... they are there for a reason.

[Alastair E]

Re: Tv Inverter works without Output caps but why?

You're driving a gas/mercury discharge-lamp. those disc ceramics are there for hash supression, nothing more.

I have been known to hack 'em out with no negative effects--Who these days listens to long-wave radio after all!

[reessi]

Re: Tv Inverter works without Output caps but why?

Thanks for replys. Some conflicting replies though, so some clarfication, I replaced with:
Blue ceramic cap:
3KV 4.7nF

From ebay:

http://www.ebay.co.uk/itm/2312562422...%3AMEBIDX%3AIT

The same as original.

They were connected right next to the lamp sockets so paralleled on the output.

See attached pic. Only 2 caps were connected one on each pair. See arrows showing one for one of the pairs. The spaces on the board for more were not populated.

Thanks.

[ReeceyBurger123]

Re: Tv Inverter works without Output caps but why?

You're driving a gas/mercury discharge-lamp. those disc ceramics are there for hash supression, nothing more.

I have been known to hack 'em out with no negative effects--Who these days listens to long-wave radio after all!

Ahh my bad I thought he removed the input caps lol

[reessi]

Re: Tv Inverter works without Output caps but why?

Looks like we're in agreement that they're to stop interference, but any idea's why replacing with good ones stops the backlights coming on? The picture still comes on and can be seen with a flashlight.

Thanks.

[rievax_60]

Re: Tv Inverter works without Output caps but why?

Usually capacitors in that area are there to tune the resonant frequency of the secondary circuit. 4.7nf doesnt sound right. Are you certain that the originals are this value?
Take a photo of the other side of the PCB if you get an opportunity.
Did the back lights not work at all originally or did they light for a short time?

[Th3_uN1Qu3]

Re: Tv Inverter works without Output caps but why?

Yes, no way 4.7nF is the right value there. I think it was 4.7pF

[reessi]

Re: Tv Inverter works without Output caps but why?

Ah, looks like I ordered the wrong value then, I'll try and find the originals and check the markings. The new ones are def nF.

Cheers.

[reessi]

Re: Tv Inverter works without Output caps but why?

Oh and to answer rievax_60, the backlights did not light even for a second when I first looked at the tv.

Cheers.

[dick_barton]

Re: Tv Inverter works without Output caps but why?

Ah, looks like I ordered the wrong value then, I'll try and find the originals and check the markings. The new ones are def nF.

Cheers.

That's why I asked for photo's of the old and new with their markings shown in just this event.

[Th3_uN1Qu3]

Re: Tv Inverter works without Output caps but why?

You are lucky that your inverter works like that. Usually that capacitor has the purpose of making a LC resonator circuit with the inductance of the transformer. This generates the high voltage necessary to strike the CCFLs. If that capacitor is burned or missing the result is usually the same - no backlight at all, not even a flash, as the voltage cannot get high enough to strike the lamp.

[culcuhain]

Re: Tv Inverter works without Output caps but why?

You're driving a gas/mercury discharge-lamp. those disc ceramics are there for hash supression, nothing more.

I have been known to hack 'em out with no negative effects--Who these days listens to long-wave radio after all!

Some of us do... and Shortwave too...