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Color Classic power issues

ravuya

Active member
I recently picked up my second Color Classic (to perhaps serve as a parts source for the working one I already possess, which has an ugly screen discoloration at the top-left and which doesn't seem to be degaussing). I put in a new PRAM battery as the machine was missing one, assuming that was the reason the computer was sold as not being able to turn on its video.

The machine powers on immediately as soon as the back power switch is flipped to "on" (as opposed to my other Color Classic, which only powers on if the power button is hit on an attached keyboard). It then emits a series of periodic high pitched squeaks which sound electrical in nature (but not quite like the arcing I've heard on blown flyback transformers on Mac Pluses) and this continues while the machine is powered on. The speakers work and play the startup chime and volume beeps so I don't believe it's a PCM sound the computer is producing.

The computer seems to be working (I can zap the PRAM, reboot the machine from the keyboard, and change the volume from the front panel switch) and seemingly is able to get into the OS, but the monitor never displays anything and doesn't seem to be getting any power (no "static electricity" sensation). The case fan is working, and the hard drive is extremely loud, which should probably be expected from a machine from 1993 on probably its original drive.

I haven't had a chance to crack the machine open to take a look at the monitor, but the fact that it powers on immediately from the power supply is interesting to me. I'm not very clear on how soft power on Macs actually works (outside of the ADB interrupt triggering it). What would make the machine power on immediately? Is there something funky with the "pseudo-softpower" compact Macs that makes it skip the ADB power switch if something else is broken along the line?

Thanks in advance for any advice for this rather vaguely-explained problem. :p

 
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