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Separate Flyback Capacitor on Circuit board.

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Harry

Thu Apr 26 2012, 09:12PM

Registered Member #4081 Joined: Wed Aug 31 2011, 06:40PM
Location: UK
Posts: 139

So I was taking apart a 36 inch CRT TV (Toshiba 36zp18q) and I found a monster flyback (as expected) and separate from the flyback was what looks like a capacitor, mounted directly on the PCB

Anyone have any ideas on the voltage ratings/capacitance of it? On the back it said 33.2KV, so I'm guessing around 40KV?
Thanks, Harry.

Thomas W

Thu Apr 26 2012, 09:25PM

Registered Member #3324 Joined: Sun Oct 17 2010, 06:57PM
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Posts: 1276

the second thing is a doubler

Alex M

Thu Apr 26 2012, 11:56PM

Registered Member #3943 Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552

As Tom Williamson said it is a voltage doubler. Does it have any pins on the bottom? if so then you might be able to access the internal capacitors, one of the HT wires will be one side and one of the pins will be another. Check it with a capacitance meter to be sure.

Harry

Fri Apr 27 2012, 06:56AM

Registered Member #4081 Joined: Wed Aug 31 2011, 06:40PM
Location: UK
Posts: 139

Thanks for the replies.
@Alex1M6 It has 6 pins on the bottom, all with traces connecting to pin 4 of the flyback, I'll assume that's ground. Sadly I do not have a capacitance meter so cannot check, and both of my ZVS drivers are broken (fed them 100 volts, the flyback was covered in corona it was amazing).

So is the flyback AC then? The core looks like it will handle around 700VA so that would be pretty good.

Alex M

Fri Apr 27 2012, 07:49AM

Registered Member #3943 Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552

Harry wrote ...

Thanks for the replies.
@Alex1M6 It has 6 pins on the bottom, all with traces connecting to pin 4 of the flyback, I'll assume that's ground. Sadly I do not have a capacitance meter so cannot check, and both of my ZVS drivers are broken (fed them 100 volts, the flyback was covered in corona it was amazing).

So is the flyback AC then? The core looks like it will handle around 700VA so that would be pretty good.

Its defiantly a DC flyback. They have probably used the doubler since it was for for a larger CRT.

Do you have a continuity function on your meter? If so see if pin 4 on the flyback transformer connects to an earth/ground point on the board. The cage around the tuner should be at earth.

It might just have 6 pins mainly for physical support, perhaps since it probably has some weight to it.

Ah yes its quite a sight when you have one of these transformers driven to destruction and bathed in lovely blue corona! What happened to your driver, did something go bang?

Alex.

Steve Conner

Fri Apr 27 2012, 08:55AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Well, if it's a DC flyback (which I agree it is) then the lump can't be a doubler, as doublers require AC to work. It must be a capacitor.

Proud Mary

Fri Apr 27 2012, 09:17AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

To the best of my knowledge, so-called "AC flybacks" have not been manufactured in the modern era. The device in the picture is certainly a 'diode split' LOPT, since you can see the focus pot and focus output wire. Where external voltage multipliers were used, as in 1970s teles, the focus lead emerges from the external multiplier module, and not from the body of the LOPT.

Why not look up the part number of the LOPT, and see if HR Diemen has a datasheet for it?

Harry

Sat Apr 28 2012, 07:05AM

Registered Member #4081 Joined: Wed Aug 31 2011, 06:40PM
Location: UK
Posts: 139

@Alex1M6 The circuit is now separate from the TV, but I can't see any traces from pin 4 apart from to the capacitor. And it is quite a chunky beast (about the size of a regular flyback) so that would probably explain the 6 pins. And weirdly, the flyback is fine, it's just the driver, in the stages of testing it now but a diode and a 'FET are broken, maybe a few more components (Zeners?).

@Steve Conner That's why I thought it was an AC flyback, because of the doubler :)

@Proud Mary No joy at HR Diemen, I found a thread about the repair of this model of TV and it said there was an external capacitor mounted on the board.

I am going to assume that the two red leads are both connected to the same side of the capacitor, and use a resistor and a voltmeter to work out the capacitance.
Thanks for the help everyone, I'll let you know how I got on.

Harry

Mon Apr 30 2012, 06:38PM

Registered Member #4081 Joined: Wed Aug 31 2011, 06:40PM
Location: UK
Posts: 139

Sorry for the double post, but I have new, intriguing information about this mystery device.

It has and input and an output for the HV, and strangely, it measures 10K ohms between the two. Also, the pins that were connected to one of the flyback's pins, it turns out that this pin, pin 4, is connected to the core via a metal strip! Strange . . .

I have ordered some new parts for a Mazzili driver and will try it out when that's up and running.

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