Advice wanted: epoxy replacement on flyback

[VicNor]

I got a machine with a good analog board, but the flyback looks a bit rough around the epoxy with some indication of arcing. I remember an old video from Adrian Black (Adrian's digital basement) where he talked about the epoxy on B&W Macs are absorbing moisture and that he replace it.

My question: Is there a way to remove the old and apply new epoxy? And what kind would you use? I mean, it needs to be able to handle 10-12 000 V and preferrably not be conductive.

 

[Paolo B]

Just my experience, but some other people may have different opinions, more educated feedback.
The epoxy blob has no actual electro-magnetic function, it just makes sure that the assembly remains glued together.
The insulation (separation) between the two magnetic circuits is guaranteed by the white plastic sheath that you see underneath, which runs all the way through the core.
One of my machines has a refurbished flyback where I replaced the epoxy collar with a silicon one. Works flawlessly.

 

[VicNor]

Just my experience, but some other people may have different opinions, more educated feedback.
The epoxy blob has no actual electro-magnetic function, it just makes sure that the assembly remains glued together.
The insulation (separation) between the two magnetic circuits is guaranteed by the white plastic sheath that you see underneath, which runs all the way through the core.
One of my machines has a refurbished flyback where I replaced the epoxy collar with a silicon one. Works flawlessly.

Thanks a lot! What kind of silicon do you use? Are we talking normal silicon you use when working on your car?

 

[Paolo B]

If I remember correctly, the actual function of the epoxy is to keep in place a plastic wedge that in turn keeps the assembly tightly packed together.
I guess the vibrations induced by the pulsating nature of the circuit may loosen it up, hence the epoxy.
I used red silicone paste for high temperature automotive applications.

 

[JDW]

The epoxy blob has no actual electro-magnetic function...

What are your thoughts on what Larry Pina says on page 96 below regarding "ringing noise" caused by broken epoxy seals?

Macintosh Repair & Upgrade Secrets 1990 : Free Download, Borrow, and Streaming : Internet Archive

Macintosh Repair & Upgrade Secrets 1990

archive.org

I was talking about that way back in 2008 here.

I've also been told by others that it's not epoxy (despite Larry Pina calling it that), and I mention that in the following thread:

https://tinkerdifferent.com/threads/flyback-glue-sealer.173/#post-894

There's a discussion on the EEVBlog about "yellow glue" here too:

Flyback Transformer, Cracked Epoxy Repair - Page 1

Flyback Transformer, Cracked Epoxy Repair - Page 1

www.eevblog.com

Here's an EEVBlog thread I started which pertained to the epoxy/yellow-glue:

Flyback Transformer, Cracked Epoxy Repair - Page 1

Flyback Transformer, Cracked Epoxy Repair - Page 1

www.eevblog.com

@techknight once said the epoxy/glue is on the flyback to prevent "mechanical resonance":

Can anyone explain the importance of glue on the Flyback Transformer?

I hope someone can, because I do not understand why it's there and what it does.

68kmla.org

 

[Paolo B]

the epoxy/glue is on the flyback to prevent "mechanical resonance":

I would tend to agree. The amount and the pattern of the resin (whatever it is) seems to be random, like something dispensed by an industrial gun.
The pulsating (alternating) nature of the current is sufficient to induce fatigue in the components, till they break (As we’ve seen in another thread).
The glue probably acts as a damper and also for keeping in place the plastic wedge that keeps the assembly tightly packed. Else, the tolerances between the parts would be sufficient to induce rattling noise.

 

[techknight]

I would tend to agree. The amount and the pattern of the resin (whatever it is) seems to be random, like something dispensed by an industrial gun.
The pulsating (alternating) nature of the current is sufficient to induce fatigue in the components, till they break (As we’ve seen in another thread).
The glue probably acts as a damper and also for keeping in place the plastic wedge that keeps the assembly tightly packed. Else, the tolerances between the parts would be sufficient to induce rattling noise.

Not only that but audible ringing. if the core is loose, it'll vibrate at the line frequency as well as all of the harmonic/fundamentals so youll hear it sometimes. Glue stops that.