Help with CRT image on Macintosh Classic I

[Aldover1595]

Hello Tinker Different! I finally got my very own compact mac, a dream of mine. It works very well now after a recap, both logic and analog board.

The CRT image has a slight dip at the top and middle, almost like Mr. Macintosh here is scowling at me (this also warps straight lines down towards the center in the image). Another, the left and right top corners appear to flick towards the center (vertically speaking) of the screen. The side and bottom of the edges are both completely sharp and normal.

Any ideas? Could it be an incorrect capacitor or as simple as a tweak to the CRT controls?

Many thanks!

UPDATE 1:
As per _nec6678's suggestion, I fiddled with the adjustments on the analog board itself. No changes to image in regards to the dip nor twitching image. I have yet to re-position the yolk assembly itself.

UPDATE 2: All Good.
Based on what I learned here, I managed to successfully adjust the screen geometry. While not perfect, I no longer have a scowly mac, or one with cocked eyebrows. Thank you!

 

[_nec6678]

Hello Tinker Different! I finally got my very own compact mac, a dream of mine. It works very well now after a recap, both logic and analog board.

The CRT image has a slight dip at the top and middle, almost like Mr. Macintosh here is scowling at me (this also warps straight lines down towards the center in the image). Another, the left and right top corners appear to flick towards the center (vertically speaking) of the screen. The side and bottom of the edges are both completely sharp and normal.

Any ideas? Could it be an incorrect capacitor or as simple as a tweak to the CRT controls?

Many thanks!

PS: Sorry if the images aren't the best, still learning how to photograph CRTs.

Are you testing it without the back case on? I've noticed that when I test my Mac Plus without it's back shell on, the image becomes somewhat distorted, maybe with some ripples. Was it doing this before you recapped it?

 

[Aldover1595]

Are you testing it without the back case on? I've noticed that when I test my Mac Plus without it's back shell on, the image becomes somewhat distorted, maybe with some ripples. Was it doing this before you recapped it?

I am currently running it with the back shell on. As far as I am aware, the machine wasn't working originally. The original owner had done some work on it as evidenced by several reworked traces on the logic board as well as most of the recap. I am no longer in contact with him, but he is knowledgable. When I initially powered it on after the trade, it exhibited the same symptoms I am having now. I didn't notice the flickering corners until later.

I forgot to mention that I have a BlueSCSI V1 installed directly below the CRT, not sure if that could be causing issues.

 

[_nec6678]

I'm not really an expert on CRTs, but a quick Google search suggests that adjusting the deflection yoke might fix your problem.
Just to be sure however, maybe try adjusting three of the four variable resistors accessible on the side of the analog board facing outwards from the machine first, marking the original positions just in case this doesn't work and you need to adjust them back. The variable resistors you need to access should be labeled as height, width, and focus on the white sheet covering that side of the board.
And also, just to be sure, there's nothing magnetic being held near the screen, right?
I found these sources for adjusting the yoke:
https://www.reddit.com/r/crtgaming/comments/1fjpd5x

Below is a picture of my disassembled Macintosh SE FDHD, and I've circled the deflection yoke (the part with the copper coils).



Hope this helps!

 

[Aldover1595]

I'm not really an expert on CRTs, but a quick Google search suggests that adjusting the deflection yoke might fix your problem.
Just to be sure however, maybe try adjusting three of the four variable resistors accessible on the side of the analog board facing outwards from the machine first, marking the original positions just in case this doesn't work and you need to adjust them back. The variable resistors you need to access should be labeled as height, width, and focus on the white sheet covering that side of the board.
And also, just to be sure, there's nothing magnetic being held near the screen, right?
I found these sources for adjusting the yoke:
https://www.reddit.com/r/crtgaming/comments/1fjpd5x

Below is a picture of my disassembled Macintosh SE FDHD, and I've circled the deflection yoke (the part with the copper coils).

View attachment 21985

Hope this helps!

This most definitely will! I figured I'd have to mess with the yolk. Thanks so much NEC.

 

[_nec6678]

I just realized that I was probably wrong in telling you where your focus, height, and width adjustments were! I was thinking about my Macintosh collection, not including the Classic, which all have those adjustments inside the case. Apparently, there's a service panel that can be removed to make screen adjustments for the Macintosh Classic, meaning that you don't have to take of the case, and instead, just a cover above the power switch!

 

[Aldover1595]

I just realized that I was probably wrong in telling you where your focus, height, and width adjustments were! I was thinking about my Macintosh collection, not including the Classic, which all have those adjustments inside the case. Apparently, there's a service panel that can be removed to make screen adjustments for the Macintosh Classic, meaning that you don't have to take of the case, and instead, just a cover above the power switch!

Oh my goodness! Thats what that cover is? I thought it was a blank for a battery holder in other models. I was about to whip out the mac cracker lmao. I'll try that first and if not I'll mess with the yoke. Again, thank you.

 

[Aldover1595]

I'm not really an expert on CRTs, but a quick Google search suggests that adjusting the deflection yoke might fix your problem.
Just to be sure however, maybe try adjusting three of the four variable resistors accessible on the side of the analog board facing outwards from the machine first, marking the original positions just in case this doesn't work and you need to adjust them back. The variable resistors you need to access should be labeled as height, width, and focus on the white sheet covering that side of the board.
And also, just to be sure, there's nothing magnetic being held near the screen, right?
I found these sources for adjusting the yoke:
https://www.reddit.com/r/crtgaming/comments/1fjpd5x

Below is a picture of my disassembled Macintosh SE FDHD, and I've circled the deflection yoke (the part with the copper coils).

View attachment 21985

Hope this helps!

I tried adjusting the analog board controls themselves. No dice. Likely have to attempt reseating the yolk itself next.

 

[_nec6678]

I tried adjusting the analog board controls themselves. No dice. Likely have to attempt reseating the yolk itself next.

That’s unfortunate that adjusting the controls themselves didn’t work. Good luck adjusting the yoke, and hopefully that fixes it!

 

[S. Pupp]

You have a screen geometry problem, and need to adjust the small black square magnets around the yoke. It is a pain to do because of the danger of electrocution, and the fact that adjusting one magnet affects the settings of the two magnets adjacent to it.

Try an internet search for “macintosh crt screen geometry magnets,” and consider living with the bad geometry. One wrong move could potentially mean not living at all.

 

[Aldover1595]

You have a screen geometry problem, and need to adjust the small black square magnets around the yoke. It is a pain to do because of the danger of electrocution, and the fact that adjusting one magnet affects the settings of the two magnets adjacent to it.

Try an internet search for “macintosh crt screen geometry magnets,” and consider living with the bad geometry. One wrong move could potentially mean not living at all.

I... uhhhh.... adjusted the screen geometry magents. One hand in my back pocket and a very careful left hand maneuver in avoidance of bare copper. Then some poking with plastic picks for the ones next to the logic board. Its not a perfect job, but now I have a nice rectangle. No scowling mac anymore!

Thanks for your word of caution though.

 

[S. Pupp]

I... uhhhh.... adjusted the screen geometry magents. One hand in my back pocket and a very careful left hand maneuver in avoidance of bare copper. Then some poking with plastic picks for the ones next to the logic board. Its not a perfect job, but now I have a nice rectangle. No scowling mac anymore!

Thanks for your word of caution though.

Bravo!