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Disabling rectifier in most flybacks

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BobsYurUncle

Mon Feb 27 2006, 12:06PM

Registered Member #249 Joined: Fri Feb 24 2006, 05:45PM
Location:
Posts: 2

Hey all,
To be precise, this will be my first post however I have been actively reading these forums for little over a year now.
I figured for those of you interested in projects such as a plasma globe, this information would be quite usefull.
While there is no clean and easy way, here is a method you can use to disable the rectifier in most modern flybacks:

There are two ways to bypass the diodes. Both are a pain.

1) See attached picture. If you grind away the housing with a drum sander or belt sander, you can get down to the diodes and solder wires across them. The dust is atrocious, use a mask or respirator. In the picture, from the left, the first unit is a typical flyback. The 2nd is bypassed with an epoxy coating over the diodes and wires. You can see the diodes and wires in the picture. Only about half of each diode is left because it has been sanded away. The other two are bypassed and coated with high voltage dope so you canâ€™t see much.

2) The other way to bypass is to drive a high voltage/high current across the diodes and permanently short them. I have succeeded in doing this with a microwave oven transformer. Unfortunately, I have not been able to develop a sure fire scientific method to accomplish it. If the HV current is maintained for too long the flyback overheats and cracks the housing. So far I only created two good flybacks this way and destroyed twelve. I had hoped to better define this process before posting it.

To drive the flyback I have been using a ferrite toroid with an approximately 90 turn secondary connected to the flyback primary. I use 5 or 6 turns for the toroid primary connected to the base of the transistor and 1 or 2 turns for the feedback connected to the transistor gate. I have used both 2N3055 and MJ15003 transistors.

In order to keep credit where credit is due, all information posted was provided by the rather clever Mark Dunn of

Bobs Out

Part Scavenger

Mon Feb 27 2006, 04:06PM

Registered Member #79 Joined: Thu Feb 09 2006, 11:35AM
Location: Arkansas
Posts: 673

That's cool! I tried that once and couldn't find the "diode" could you give us a close up pic?

Kipmans

Mon Feb 27 2006, 08:54PM

Registered Member #91 Joined: Thu Feb 09 2006, 03:03PM
Location: The Netherlands
Posts: 45

Looks cool indeed, I'm going to see if I can sand off one of my flybacks too and see if I can bypass the diode.

Attached picture shows the victim; I'm guessing that the rectifier sits inside the area within the red circle (judging by the pictures in the first post). I already sanded off a very small part to see how that worked out.

BobsYurUncle

Tue Feb 28 2006, 03:59AM

Registered Member #249 Joined: Fri Feb 24 2006, 05:45PM
Location:
Posts: 2

Not Quite Kipmans, but your on the right track.
The rectifier is under the twisty knobs encased in a box of that yellow goo.
Once you grind past the twisty knobbs be carefull because the diode itself is not far behind it.
The last transformer I did this to came from Electronic goldmine and only had 1 single diode and a couple of capacitors.
I'd have a nice closeup of it however I have left my camera with the gf... damn

Here is the previous picture zoomed with the area to grind marked.

Bobs Out

Part Scavenger

Wed Mar 01 2006, 04:46AM

Registered Member #79 Joined: Thu Feb 09 2006, 11:35AM
Location: Arkansas
Posts: 673

Boy, was i digging in the wrong spot. No wonder. Thanks!

Kolas

Thu Mar 02 2006, 05:29PM

Registered Member #102 Joined: Thu Feb 09 2006, 08:15PM
Location: Raleigh, NC
Posts: 169

Of course, this is completely off toppic. But hey, you seem to like destroying things

Me too!
What all is in one of those flybacks? I get the basic idea of whats in there, though I'm wondering where they are placed in the device. It should be considered that not all flybacks have those "twisty knobs" where do i look for the diode(s) in one w/o?

Kolas

Part Scavenger

Thu Mar 02 2006, 11:18PM

Registered Member #79 Joined: Thu Feb 09 2006, 11:35AM
Location: Arkansas
Posts: 673

I haven't seen a modern FBT without twisty knobs... To find out what all is in a FBT, there's schematics for them on the net, there was also a thread on this in the old forum.

robert

Thu Mar 02 2006, 11:28PM

Registered Member #188 Joined: Thu Feb 16 2006, 05:18PM
Location:
Posts: 67

I recently opened up a broken LOPT with a chisel.
I could extract (all of it damaged):
-7 diodes (about 1,5cm long 4mm thick)
1 capacitor about 4cm long, 1cm thick and 2.5cm wide
1 capacitor 3cm long, 0,75cm thick and 1.5cm wide
2 high value resistors (zigzag trrack glazed on ceramic)
the focus divider assembly

Part Scavenger

Thu Mar 02 2006, 11:33PM

Registered Member #79 Joined: Thu Feb 09 2006, 11:35AM
Location: Arkansas
Posts: 673

Here's the link for the old forum.

skmetal7

Sat Mar 04 2006, 09:33PM

Registered Member #101 Joined: Thu Feb 09 2006, 08:12PM
Location: Wisconsin
Posts: 41

i felt like taking some frustrations out on a flyback today:

i've never seen such fine windings before, what gage is it?

if i can find the ends ill see if it still works

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