SE/30 CRT Geometry knobs

[ktkm]

Hello before I die!

After watching techknight’s video regarding CRT Swaps, I was intrigued how easy it looks. After much consideration I’m thinking of performing something similar with an SE/30. However, one thing the video won’t explain is how exactly the knobs work (see attached image). 

1. First of all, are they safe to touch with your bare hand?

2. There are eight knobs, but which knob affects exactly what part of the screen geometry?

3. Once moved/rotated are they stable, or do they need glue of som sort to stay fixed?

4. Two of them (2 and 3 in the attached image) seem hard to reach, how are they best dealt with?

Has anyone here done this successfully?

Sincerely,

ktkm

9_inch_crt-geometry-1.pdf

 

[bibilit]

Only had to perform it once.

Most of the time, you don't need to touch those, except if the screen has been badly handed or someone has moved the knobs in the first place.

It's not safe to touch them with bare hands, i use wood sticks.

 

[ktkm]

Only had to perform it once.

Most of the time, you don't need to touch those, except if the screen has been badly handed or someone has moved the knobs in the first place.

It's not safe to touch them with bare hands, i use wood sticks.

“Only had to perform it once.”

– When you did perform it, how did turn out? Was the Mac fully assembled, or did it involve any other preparations?

– Do you remember which knob you turned and what it did?

“Most of the time, you don't need to touch those, except if the screen has been badly handed or someone has moved the knobs in the first place.”

– I have to touch them, the video have very annoying corner peaks and tilts.

“It's not safe to touch them with bare hands, i use wood sticks.”

– What I mean, I think, are the knobs conductive or is your use of wooden sticks just a safety measure?

 

[bibilit]

“Only had to perform it once.” – When you did perform it, how did turn out? Was the Mac fully assembled, or did it involve any other preparations? – Do you remember which knob you turned and what it did?

On a Classic II IIRC, helping BadGoldEagle to correct some geometry issues, fully assembled, don't remember which one, was not perfect...better.

You are very close from the CRT, and high voltages, so yes wood is a safety measure.

Maybe a picture will be helpful.

 

[ktkm]

Here is a representation of my raster problem.

 

[ktkm]

Here’s the CRT from the PDF.

 

[BadGoldEagle]

Yes, Classic II and BTW, it's getting worse and worse (the high pitched sound came back), but that thing has terrible caps all round.

I had to do those adjustments again because the cat broke the CRT neck on me Classic (not II)! The back case on top of the living room table and the Classic was right beneath the said table (I was working on it and since I have a carpet floor, it's very scratch proof, so I tend to work a lot on my knees). Cat jumped from there to the china closet and took the case along with him for a short ride. And guess where it fell? Yes, on the poor CRT's neck. It was a good CRT, in perfect health too. RIP in pepperoni. But hey I might use it for some hack some day (already have the hack in question in mind!)... I was properly sad that day, but now I've sorta recovered (the CRT hasn't  [] ]'> )

Anyway... When I did the adjustments with the "new" CRT, I went bare hands (had one arm behind my back just to be sure and only one hand was allowed to touch the magnets.)

YOU HAVE TO BE REALLY FOCUSED ON WHAT YOU'RE DOING BUT if you are, then it's pretty easy.

Some tips: for the magnets labeled 2 and 3 in your PDF, I suggest using what bibilit already suggested: the mighty kebab sticks! Super useful when it comes to adjusting the potentiometers on the side of the Analog board too. 

You just can't reach down, you're hand would be too close to some dangerous parts!

Just play around with the magnets, you'll find the right adjustment soon enough.

NB: If the whole display is tilted, move the whole yoke assembly but you can't do that while the unit is on.

 

[ktkm]

“Just play around with the magnets, you'll find the right adjustment soon enough.”

– I see, but when you’re done, do you glue them in place?

 

[BadGoldEagle]

No need to. They don't move that much once in place, you'll find that there is still some resistance and some elasticity to their rotation. You'd need to glue them in if you intend to use your SE/30 as a maraca... which is still very unlikely to happen.

 

[ktkm]

No maraca!? Dang!  [] ]'>

Thank you bibilit and BadGoldEagle for the help so far!

(If I succeed I’ll make a excessive documentation.)

 

[techknight]

these adjustments are documented in the SE/30 service information from apple. Of course apple doesnt host it anymore, but I think it can be found on various vintage mac sites. 

The geometry magnets wont be covered in the manual though. 

 

[Scott Baret]

I have done this adjustment--and have done it with bare hands. It is difficult indeed, but if you've got severe geometry issues and don't want to swap your CRT, it's the only way to go.

The key is to be:

1. Extremely careful.

2. Extremely meticulous. 

I advise doing this with a large mirror in front of you. 

 

[BadGoldEagle]

I advise doing this with a large mirror in front of you. 

+1.

Very useful indeed!

 

[ktkm]

these adjustments are documented in the SE/30 service information from apple. Of course apple doesnt host it anymore, but I think it can be found on various vintage mac sites. 

The geometry magnets wont be covered in the manual though. 

Yes, I noticed that. They only cover the centering rings … as if that would be safer?

I have done this adjustment--and have done it with bare hands. It is difficult indeed, but if you've got severe geometry issues and don't want to swap your CRT, it's the only way to go.

The key is to be:

1. Extremely careful.

2. Extremely meticulous. 

I advise doing this with a large mirror in front of you. 

Was it recently? Is the raster stable today?

I’ll get the mirror, thanks for the tip.

 

[techknight]

Another thing that CAN help is to demagnetize the electron gun assembly. 

I used to do this in the color CRT days when I ran into purity problems that I could never resolve, I took an old degaussing coil for the TV service man, and demagnetized the gun assembly. That seemed to work on alot of it. 

These days its nearly impossible to find a TV servicing degaussing coil, But, its much easier to find pull-trigger soldering guns which have a big transformer in it, which basically does exactly the same thing although not quite as strong. 

 

[Scott Baret]

Was it recently? Is the raster stable today?

I haven't done one of these in a while, but I have done a good deal of them since I studied the procedure about 14 years ago. It did stabilize the rasters in the machines, and if proof is needed, I gave an SE/30 I did this on to my uncle and his daughter and the screen still looked good when I visited them last year. (I do need to get them a new PRAM battery though, and I'm sure it needs recapped by now!)

 

[ktkm]

Another thing that CAN help is to demagnetize the electron gun assembly. 

I used to do this in the color CRT days when I ran into purity problems that I could never resolve, I took an old degaussing coil for the TV service man, and demagnetized the gun assembly. That seemed to work on alot of it. 

These days its nearly impossible to find a TV servicing degaussing coil, But, its much easier to find pull-trigger soldering guns which have a big transformer in it, which basically does exactly the same thing although not quite as strong. 

Sounds like good idea, but I’d love to watch that movie first, since I think it is a little out my grasp. Good work!

I haven't done one of these in a while, but I have done a good deal of them since I studied the procedure about 14 years ago. It did stabilize the rasters in the machines, and if proof is needed, I gave an SE/30 I did this on to my uncle and his daughter and the screen still looked good when I visited them last year. (I do need to get them a new PRAM battery though, and I'm sure it needs recapped by now!)

That sounds comforting! Thank you!