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Brightness Knob on Macintosh SE

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Hey! The brightness knob on my Macintosh SE doesn't seem to work all of the way. It goes from medium-bright up to very-bright... but it does not go below medium-bright. It stops very suddenly at medium-bright and does not get any dimmer. I would like to be able to turn the brightness all the way down to basically shut the CRT off to preserve it.

 

Is that just a dirty potentiometer? I cleaned out a Gameboy contrast pot last night by running isopropyl alcohol over it while rotating it... would that work on my Macintosh SE? I just wanted to check before digging the analog board out of there.

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So does the knob continue to rotate and just not dim the display further, or does the knob stop while the display is still medium bright? If it's the former you've probably got an issue with the pot but if it's the latter you'll need to make some adjustments to your analog board to bring your brightness and/or contrast levels within spec so that the pot has the desired effect.

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25 minutes ago, Franklinstein said:

So does the knob continue to rotate and just not dim the display further, or does the knob stop while the display is still medium bright?

The knob continues to rotate, it just doesn't get any dimmer. Dirty potentiometer? Pull the board, flush with alcohol while turning the knob, and let it dry out for a couple of hours?

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Quote

The knob continues to rotate

The knob should not rotate permanently, only go from a minimum to a maximum from the middle position.

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6 hours ago, bibilit said:

The knob should not rotate permanently, only go from a minimum to a maximum from the middle position.

I should have been more clear, it does not rotate indefinitely. It does stop rotating, but it doesn't go any dimmer than "middle-bright".

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Do you see any scan lines when the pot is turned up for full brightness? They are the diagonal lines that zig-zag across the display, and they shouldn't be visible.

 

If they are, you may have to adjust the cutoff, as it is probably set too high.

 

c

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