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I've figured it out. It's the vertical scale you've set both your probes to. Try 1V or maybe even 500 mV per division.

Good video. Don't give up. Something is just not right about the noise floor on your oscilloscope. There is no way there is basically a 1V difference between your two probes. Could you email Rigol support and ask what the expected level should be for your scope in A-B math mode? I think we need...

Although the setup looks correct, the 800 mV noise floor is freaking me out. It should be an order of magnitude lower. Am I being tricked by the 10x probe? In any case, you definitely see the difference in the final two images from the scope. Even if the scale is off or the base noise is higher...

I have edited my prior message to now say 'math-subtract' mode to avoid confusion for future readers. Originally, I used the word 'differential' which may not be the right terminology.

Your Rigol scope is perfect for this test. For this, we care about the scope feature, not the probes. I assume both of your probes are in 10:1 configuration? Put the CH1 probe on U15B pin 12. Put the CH2 probe on U15C pin 12. I guess connect the ground of both probes together. Funny, I haven't...

I suspect the LCD electrical noise is being injected (or not filtered) in the above area of the circuit. Here's what I would check: 1. Obviously look carefully for loose pins or corrosion in this area. I suspect you've already done this. Any resistance on the ground or power supply connections...

My hope is that if you can reproduce this on demand by varying the pixels on the display, it: 1. May help you follow the noise through the circuit. 2. May suggest a problem with the LCD grounding/filtering 3. May suggest there is a grounding or filtering issue on the sound circuit, as opposed to...

Feedback from the LCD driver rather than the code that is running? Notice that the sound changes exactly as the screen changes images. "Welcome to Macintosh" (whine changes) "gray before Finder appears" (whine changes) "Finder window appears" (whine changes) "Chooser appears" (whine changes)...

Thank you for your thoughtful reply. One of the things I've learned to value the most in life is when someone is willing to share their perspective with you, particularly on deep and sensitive topics. There is no greater human gift. Not at all. Your post is genuine and positive. - David P.S...

Similar to nearly everyone on this forum, I enjoy talking about old computers and I am kind to others. If you are like that, then you are my friend. This hobby takes me away from the stresses of politics, social issues, and global conflicts. I would be less likely to participate in any group...

If you control the applications, you could always just register a gestalt value that contains a pointer to a buffer or callback methods. Edit: I now see you want to do it over a network and not within the same machine.

Upgrading the Color Classic board with +256KB of VRAM allows it to display 256 colors @ 640x480 when installed in the Performa 550.

Yes. It works fine and defaults to 640x480. This is an unmodified Color Classic motherboard (LB) in an unmodified 550 (analog board + display). Extra VRAM is not installed, hence 16 colors.

That's pretty cool. Based on the picture, I thought it was a 7300/7600 card. It should just pop in and work. Upon reading, I understood it was more interesting and it needs software to kick in.

Is there corrosion on the inner contacts of J3? Or is that just a reflection? Is J3 connected to anything when the board is installed?