what is going on here

[Alex Eisenhut]

My NEC 9" CRT monitor has this odd structure in it... I don't get it. Never seen anything like it, it looks like crap. How can this be?

[T3sl4co1l]

 

Did you forget to circle something?  Did you mean the whole thing?

It's not obvious if the bottom chassis/mounting plate is rigid to the CRT mount, as I can't see the bottom.

Maybe the neck board needs a bracket or pad (those things can shake loose), but there can be a foam rubber pad on the outer casing, which also isn't shown.

So, I don't get it... 

Tim

[HAL-42b]

Two HT coils though. Interesting.

[voltz]

"It looks like crap".

Its pretty standard as CRT monitors go... HT cables, springs around the tube, metal brackets etc.. they're all like that.

[Alex Eisenhut]

I'll take another picture later, but do you see what appears to be a rubber grommet floating in mid-air over the acquadag of the CRT?

It's a weakish magnet. It's not very strongly attached either. Worse yet, it's part of that sheet-metal bracket over the flyback.

So I don't get what's the purpose of a floating magnet in space except to pre-distort the image somehow, but to what purpose? At that point, the electron beam is well accelerated, and there are already the usual purity magnets over the CRT neck.

Is it to compensate for the speaker magnet?

Now that stupid sheet-metal bracket, it screws into the frame, but also to the top of the flyback. I've never seen a flyback used structurally before.

But I've never worked with TVs much, so maybe it was standard to have magnets floating around unsupported thereby changing the set's color after it's shipped from the factory and it's tossed around in shipping...

I really don't get it. Unless someone says "yeah sure, that's a Troglotron setup, standard on all color CRTs since 1954, duh".

[Alex Eisenhut]

...maybe it was to compensate for the speaker magnet of another identical monitor to its left?

[T3sl4co1l]

Ah, okay. I noticed that, couldn't decide if it was a correction magnet or a rubber bumper.  Yes, correction of some sort or another; for the speaker?  Possible.

I've seen sets with arrays of correction magnets (like this, but smaller, and more of them) arranged around the periphery of the yoke.  How much that's *really* necessary (in terms of a rectilinear, undistorted picture, and color purity), I don't know.  It's all very low level adjustment stuff, so you put it in if you need to, and twist them around until it looks right.  Who knows.

Tim

[Cubdriver]

Is it possible that the flyback is not being used structurally, but instead that the sheet metal bracket is to hold both the flyback AND the support arm for the magnet?

-Pat

[T3sl4co1l]

I've seen that before, screws in flyback transformers.  Doesn't bother me -- have you ever tried to break one apart?  Let me tell you, they use something like diamond-filled epoxy in the bastards! 

Tim

[Alex Eisenhut]

Oh no, that was snapped off as well. I just never saw something like that before. I'm taking the whole mess off and gonna see what the picture looks like.