I recently acquired a nice example of a Mac Color Classic, well cosmetically anyway. When I turn on the power switch I hear what sounds like the power supply and the screen powering up, but the fan never gets going and nothing else happens. I have tried attaching 3 different ADB keyboards to no avail. The funny thing is that if I remove the logic board and power the system on the fan starts up! The logic board has NOTHING installed in any of the exansion slots. No RAM or VRAM. Could this be the problem? I thought CCs had soldered in RAM and VRAM. Do I need to fill these slots for it to work? Any other ideas?
Thanks! 
Andrew
Yes, it needs RAM, but not VRAM.
The CC comes with 4MB RAM soldered to the logic board. No VRAM is soldered to the logic board. So if the VRAM slot is empty, that could be your problem.
Matt
_My_ Colour Classic has 2x1mb SIMMs in the RAM slots and no VRAM SIMM installed
For what it's worth, my CC developed cold joints in the analog board which did all sorts of screwy things. Could be worth checking.
Wouldn't hurt to test the battery either.
Um... I forgot about this... But there is no battery installed... I thought this just kept the clock going when the power is off?
As far as the RAM and VRAM issues... I am now more confused than ever.
For sure, the Color Classic has built-in VRAM, so a VRAM SIMM is unnecessary. However, I haven't found any information that says if there's RAM soldered to the motherboard--so I would assume RAM SIMMs are necessary.
A battery is necessary on some machines (some LCs, Quadras, Performas and Power Macs), including the CC, in order to get video on bootup. For some reason the video chip needs there to be a battery with at least about 2.5 volts output in order to work. A trick to get by this is to power up the machine, then power it off and immediately back on again (no longer than a second between off and on). This seems to "kickstart" the video chip.
My bad on the VRAM -- 256k is indeed onboard.
As for RAM, 4MB is also onboard, soldered onto the mobo. This is documented in the Apple Service Manual and in many other sources.
As for the PRAM battery, according to the CC FAQ, A CC will boot fine without a PRAM battery. (It will also boot with a bad PRAM battery but won't display video.)
Matt