I am in the midst of repairing a Classic II. It was very clean inside, with the PRAM battery intact and the expected amount of capacitor leakage. It's fully-functional after replacing the electrolytics on the analog and main boards. Even the original HDD still works. The floppy drive needs some love, but that's for another day.
But there is a weird audio issue that I'm trying to track down.
The speaker emits a squealing tone that constantly changes in pitch. It starts high and goes low, sort of like a bomb whistling as it drops. It takes about 20 seconds, then cuts out and starts over again. It gets quieter the longer the Mac is powered on, but it's still noticeable. Plugging in headphones works as expected: the speaker mutes, and the bad tone comes from the headphones. Otherwise, the audio sounds fine.
Here's the weird thing. By putting pressure on the main board and causing it to flex, the tone's pitch changes! What in the world?! There must be some physical component to this problem. I used the patent-pending Wooden Poking Spoon™ to ensure the circuit wasn't electrically affected.
The board was cleaned in an ultrasonic bath with Branson EC cleaner, but there was no improvement.
Any suggestions for where to begin debugging this?
But there is a weird audio issue that I'm trying to track down.
The speaker emits a squealing tone that constantly changes in pitch. It starts high and goes low, sort of like a bomb whistling as it drops. It takes about 20 seconds, then cuts out and starts over again. It gets quieter the longer the Mac is powered on, but it's still noticeable. Plugging in headphones works as expected: the speaker mutes, and the bad tone comes from the headphones. Otherwise, the audio sounds fine.
Here's the weird thing. By putting pressure on the main board and causing it to flex, the tone's pitch changes! What in the world?! There must be some physical component to this problem. I used the patent-pending Wooden Poking Spoon™ to ensure the circuit wasn't electrically affected.
The board was cleaned in an ultrasonic bath with Branson EC cleaner, but there was no improvement.
Any suggestions for where to begin debugging this?
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