Screen Adjust on a Mac Classic?

[Tempest]

I have a nice looking Macintosh Classic, the only problem is that the image is slightly tilted to the right. It needs a little adjustment to make everything right again. What's the best way to do this? I know on earlier macs there were some adjust pots on the side of one of the boards (next to the monitor). I noticed that in the back where the battery compartment used to be there's a whole bunch of holes that look like adjusts of some sort. Is there a way to do it through there? I played with the two that looked like they had a head I could turn with a screwdriver and one was brightness and I'm not sure what the other did (sound?). There are a ton back there that I didn't try because they just look like holes.

Tempest

 

[aftermac]

To adjust the tilt of the monitor you have to adjust the yoke on the back of the CRT. The adjustments section of the service manual explains how to do this:

http://www.apple-collection.com/CarPos/classic_ii_performa_200.pdf

 

[Mars478]

To adjust the tilt of the monitor you have to adjust the yoke on the back of the CRT. The adjustments section of the service manual explains how to do this:
http://www.apple-collection.com/CarPos/classic_ii_performa_200.pdf

Which I may add is one of the most dangerous things to do to a CRT.

 

[Dog Cow]

I know on earlier macs there were some adjust pots on the side of one of the boards (next to the monitor).

Yes, but you might not need to open the case. Read on....

I noticed that in the back where the battery compartment used to be there's a whole bunch of holes that look like adjusts of some sort. Is there a way to do it through there?

Yes, try these ones first. They adjust the screen, but there are some pots which can't be reached through there so you'd need to take the case off. Unfortunately, I haven't needed to adjust my Classic, so I don't know which aspects of the screen these pots govern. Probably at the least, width, height, and brightness.

 

[aftermac]

I know on earlier macs there were some adjust pots on the side of one of the boards (next to the monitor).

Yes, but you might not need to open the case. Read on....

I noticed that in the back where the battery compartment used to be there's a whole bunch of holes that look like adjusts of some sort. Is there a way to do it through there?

Yes, try these ones first. They adjust the screen, but there are some pots which can't be reached through there so you'd need to take the case off. Unfortunately, I haven't needed to adjust my Classic, so I don't know which aspects of the screen these pots govern. Probably at the least, width, height, and brightness.

None of the pots adjust the tilt of the monitor.

 

[Dog Cow]

None of the pots adjust the tilt of the monitor.

How do you suppose it got that way, then? Also, are we talking about a tilted screen image, or a physical tilting of the CRT? Because the CRT tilt would be controlled by the screws, I would think.

 

[aftermac]

None of the pots adjust the tilt of the monitor.

How do you suppose it got that way, then? Also, are we talking about a tilted screen image, or a physical tilting of the CRT? Because the CRT tilt would be controlled by the screws, I would think.

Not sure how it would get that way... maybe it was never perfect from the factory? Maybe the yoke screw clamp has loosened after 20 years?

I'm not sure that you can really adjust the physical tilt of the CRT. It's pretty much screwed in place.

This sounds like a tilted screen image, which is corrected by adjusting the yoke by hand on the back of the CRT. If you look at the PDF I posted above it explains how to do this on pages 108-112.

Pages 97-106 explain what each of the pots does on that back of the Classic and none of them includes tilt.

 

[Tempest]

Eek, I'm not sure I want to touch the yoke. That's seriously dangerous. Maybe I'll learn to live with it, it's not that bad...

Tempest

 

[PowerPup]

To adjust the tilt of the monitor you have to adjust the yoke on the back of the CRT. The adjustments section of the service manual explains how to do this:
http://www.apple-collection.com/CarPos/classic_ii_performa_200.pdf

Which I may add is one of the most dangerous things to do to a CRT.

Woah woah woah... You're saying that when I was about 14 and I replaced the PowerBoard in my Classic II and also had to replace the CRT yoke. That I was doing the most dangerous thing I could do when I was running the computer while adjusting the yoke!?!?

................

Cool. :rambo:

As long as your feet aren't on any carpet and make sure your hands are discharged of any static... I think you'd be fine... But you do whatever you feel safe with. I'm no expert.

 

[Tempest]

What parts of the monitor do I NOT want to touch when its running? I know the anode cap is a no-no, but what parts on the yoke? I assume the plastic ring the manual mentions to twist is ok or they wouldn't tell you to touch it.

Also, what's the best way to discharge the CRT? I've just been letting the system sit off and unplugged for several hours. Is there a way to expedite the process?

Tempest

 

[aftermac]

What parts of the monitor do I NOT want to touch when its running? I know the anode cap is a no-no, but what parts on the yoke? I assume the plastic ring the manual mentions to twist is ok or they wouldn't tell you to touch it.
Also, what's the best way to discharge the CRT? I've just been letting the system sit off and unplugged for several hours. Is there a way to expedite the process?

Tempest

Scroll down a bit on this page and it shows the best way to discharge the CRT:

http://www.biwa.ne.jp/~shamada/fullmac/repairEng.html

 

[Scott Baret]

I have adjusted dozens of yokes over the years. You can't adjust the yoke from the controls on the back of the Classic above the power switch (although there are plenty more settings there than on the analog boards of earlier Macs).

Here's what to do:

1. Open the Mac.

2. Set it upright on a non-carpet surface.

3. Loosen the Phillips head screws around the CRT.

4. Plug in and turn on the Mac.

5. Turn the coiled wires, making sure you avoid the red anode cap (which looks like a suction cup) at all costs.

6. When the desired position has been reached, turn off the Mac and tighten the screws. Make sure you don't bump what you just adjusted, or else your work will be undone.

7. Check the screen to make sure it's good.

8. Check your screws again to make sure they're tight.

9. Put the case back on the Mac.

A few points to keep in mind:

1. Avoid the anode cap at all costs.

2. Don't bump the centering rings (the little solid golden-colored rings that go around the CRT).

3. Don't bump the magnets around the neck of the CRT unless you want to mess up your geometry.

4. Avoid touching anything on the analog board.

5. You may want to adjust the size of the horizontal and vertical raster before working on the centering to make things easier. You can do this through the controls on the back of the Mac. TV adjustment tools should do the trick with these holes (you can get these at Radio Shack or online) or you can use a small screwdriver.

6. Keep in mind that the top and bottom may not align perfectly. These are CRTs, not LCDs, and all CRTs have slight geometry imperfections.

7. If you're afraid of reaching around to the back of the Mac from the front, put a mirror in front of it. Many CRT newbies do this trick until they gain more confidence in their adjustment and accident avoidance abilities. Avoid the bathroom, of course, as water and Macs don't mix.

8. HAVE FAITH IN YOURSELF!!! Many people don't attempt to do this repair because they are scared of the high voltages. However, it's really a simple fix and as long as you know what not to touch you should be OK!!!

Best of luck with the adjustment!!! Let us know how it turns out!!!

 

[tomlee59]

Scroll down a bit on this page and it shows the best way to discharge the CRT:

http://www.biwa.ne.jp/~shamada/fullmac/repairEng.html

Actually, that site gives unnecessarily elaborate advice. The discharge tool he describes is utterly useless. The high voltage simply arcs across the resistor. Don't bother with a resistor; just use a grounded tool.

That said, I'll repeat my "broken record" utterance: There is no need to discharge the crt if you are not going to disconnect it from the analog board.

 

[tomlee59]

What parts of the monitor do I NOT want to touch when its running? I know the anode cap is a no-no, but what parts on the yoke? I assume the plastic ring the manual mentions to twist is ok or they wouldn't tell you to touch it.
Also, what's the best way to discharge the CRT? I've just been letting the system sit off and unplugged for several hours. Is there a way to expedite the process?

Tempest

From your original description, I am unsure as to the actual problem. Others have concluded that your raster is simply rotated. If that's the case, then rotating the yoke will certainly fix it. If the raster has other geometric problems, then you'll have to do extra work.

In any case, assuming that a rotation will cure what ails you, follow Scott's basic procedure, with the following additional notes:

1) The yoke is glued to the crt, so simply loosening the screws will generally not allow free rotation. You will need to grab the yoke and twist steadily and firmly until it breaks free. You will likely feel nervous, but don't worry.

2) Do not simply turn off the Mac; pull out the power cord. As long as you follow this rule, it will be safe for you to stick your mitts inside.

3) When you are satisfied that the yoke is properly adjusted, tighten the yoke's retaining collar. Do not overtighten the screw, or you will break the crt. Tighten the screw only enough to prevent free rotation of the yoke. Once that's been achieved, you're done.

If you need to do more than adjust rotation, see http://68kmla.org/files/classicmac2.pdf for additional notes on what to do.

 

[shred]

Not sure how it would get that way... maybe it was never perfect from the factory? Maybe the yoke screw clamp has loosened after 20 years?

Since some of us are freighting rare Macs around the World, it's worth a bit of a mention of how the image geometry can get to be screwed up on a classic Mac.

The Earth's magnetic field interferes with the position and geometry of the image. In particular, if a Mac sold in the Northern Hemisphere is moved to the Southern Hemisphere, the image will be too far up and to the left and the sides won't be perfectly straight. I speak from experience here: the Mac 128, 512 and Plus were all manufactured and adjusted in the Northern Hemisphere without taking this in to account. Since I worked for an Apple dealer in the Southern Hemisphere, this meant that every brand new Mac had the image all messed up when it was taken out of the box. I must have adjusted hundreds of them back in the day.

Around the time the Classic came out (not sure exactly when), we started receiving machines that had pretty good geometry straight out of the box (not perfect, but pretty close). I asked one of the Apple techs about it when I was doing some training. I was told that they had started performing the factory image alignment inside a large Helmholtz Coil http://en.wikipedia.org/wiki/Helmholtz_coil. Basically, this allowed them to "dial in" the magnetic characteristics for any spot on Earth. For Australia, this meant "Sydney". I was quite some distance south of Sydney, so this explained the geometry not being perfect for us.

The funny thing was that sometimes machines would go out to the customer without being aligned. People very rarely noticed, but if someone pointed it out to them, the alignment problem would then drive them crazy until it was fixed!

[EDIT] And with colour displays, the problems are more serious: purity problems (patches where the "hue" of the colour is wrong) on top of the geometry problems experienced with black and white displays. It's *much* harder to fix a colour CRT. They had different part numbers for Northern Hemisphere / Southern Hemisphere.

 

[aftermac]

Scroll down a bit on this page and it shows the best way to discharge the CRT:

http://www.biwa.ne.jp/~shamada/fullmac/repairEng.html

Actually, that site gives unnecessarily elaborate advice. The discharge tool he describes is utterly useless. The high voltage simply arcs across the resistor. Don't bother with a resistor; just use a grounded tool.

That said, I'll repeat my "broken record" utterance: There is no need to discharge the crt if you are not going to disconnect it from the analog board.

I wouldn't bother with the resister either. However, it shows a simple way to ground it with a screw driver and a wire with alligator clips at each end. And it shows you how to ground it. Nothing really elaborate about that... it's one of the simplest diagrams for discharging a CRT that I've seen.

 

[Tempest]

Some people have asked what I'm talking about so I'll try and clarify. The picture on the screen appears to be slightly tilted. By this I mean the white bar at the top of the main OS screen is further down (lower) form the monitor bezel on the right side than it is on the left. In this case a good quarter inch. It's not the end of the world, but it would be nice to have it corrected.

I may try this first on my dead SE. Someone gave me an SE for parts and since the battery blew up on the mother board and it hasn't been powered on in 10+ years, I doubt anything is holding a charge at this point. That way I can get the feel for breaking the glue and how easily the yoke twists.

The manual says to twist the plastic ring, and not to grab the copper wires. Is this correct? I'd think touching anything on the CRT other than the plastic would give you a nasty shock.

Tempest

 

[Dog Cow]

The manual says to twist the plastic ring, and not to grab the copper wires. Is this correct?

What do you suppose usually flows through copper wiring?

 

[H3NRY]

The basic rule for working on hot electronics is keep one hand "in your pocket", meaning don't have both hands touching the machine. That way if you touch high voltage, you may get a painful shock, but the current won't travel through your heart and kill you. That said, I've screwed up my courage and reached in with one hand and adjusted yokes, magnets, and the like on many CRTs, and have yet to be bitten. Be careful, and there's little chance of getting zapped. Working on tube hi-fi amplifiers is a lot more dangerous IMHO. 8-o

BTW, the yoke doesn't carry high voltage, so it's safe to touch the coils if you have to to break it loose. Or since you know you're going to rotate it anyway, loosen the clamp and give it a little turn before you turn the computer on. That way it'll be easy to turn when it's running.