Squealing CRTs

From: Iggy Drougge <optimus_at_canit.se>
Date: Sat Oct 6 20:05:28 2001

Tony Duell skrev:

>> >The squeal from most monitors/TVs comes from the flyback transformer
>> >(horizontal output transformer, line output transformer, call it what yo=
>> u
>> >will). THe core vibrates at the horizontal scan frequency.
>> Is that the neck at the back of the tube? I see a key-like screw protrudi=
>> ng at
>> a 90=B0 angle from the neck, which seems to be coupled to a metal band wr=
>> apped
>> across the neck.

>No, that's the deflection yoke. The flyback transformer is on the PCB
>normally. The easy way to find it most of the time is to follow the EHT
>cable from the flare of the CRT back to a plastic-encased lump on the
>PCB. That's normally the flyback transformer (it could be a voltage
>multiplier in some older colour monitors, but I don't think that's an
>issue here).

All right, I stole some sticks of hot glue from the scale modellers and poured
it onto the thing which looks like this:

  | _ |
  | | |WARNING|
  | | | HIGH |
  | | |VOLTAGE|
  | | | |
  |_| |_______|
It sits on the main board in the monitor section, connected to that dangerous
red wire fit with a suction cup onto the CRT itself.

But it doesn't really look like something which will vibrate or rattle in any
way. I've done some reading up on flybacks, though, and apparently there are
some advanced wirings inside that package.

Then I let it dry and turned it on. Still the same horrible sound. I walked
around the thing for a bit, and it seemed as though the noise emanated from
the black cage containg what is probably the mains transformer.

A recent posting in the ongoing "wobbly PET" thread suggests that some sheet
steel contraption inside the PSU is dissolving and vibrating at mains
frequency. Could this be the case here?

En ligne avec Thor 2.6a.
The generation of random numbers is too important to be left to chance.
Received on Sat Oct 06 2001 - 20:05:28 BST

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