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Color Classic Analog Board problems


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So I was recently able to aquire a Color Classic with a 575 board. It was supposedly working when shipped. When I got the machine, nothing. I tried all of the normal troubleshooting steps, let it sit, unplug and replug the logic board with power switch on, clean the contacts. I also pulled the analog board and found nothing that really stood out. No blown caps, no cracks, no burn marks. 

 

When I turn the machine on, I get what sounds like high voltage, but when I press power button, All Iget is one set of three small chirps. With the logic board removed the machine just chirps. I also have no hd in it, and have removed the pram battery. Could this just be shorted logic board caps?

Edited by gobabushka
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It could certainly be failed logic board caps, or damage from leaked capacitors.  If everything were fine, the 575 board doesn't need a PRAM battery to power on in the CC chassis, so leaving it out should be fine.  I certainly can't rule out analog board trouble given the symptoms though.  The input and high voltage CRT portions might be functioning, but it may be failing to provide the right voltages, sufficient current, or stable voltages to the logic board.  I wonder about the output filtering caps.  My first step in troubleshooting would be to stick a logic board or analog board known to boot in there, but I realize not everyone has one sitting around.  Sometimes it's possible to spot logic board cap damage in photos, oftentimes it's hidden, but posting a photo of the board probably wouldn't hurt.

Edited by rsolberg
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I am guessing that you tried to boot to a boot floppy? Rsolberg has a great idea about trying to boot to a good board.  But if you do not have one, that is an expensive test.  I also suggest you slide out the 575 board and photograph the front and back then post the photos here.  Also, if you remove the case, stick your ear near the neck of the CRT. Then try to boot.  Let us know where the noise is coming from.  Is it from the rear of the CRT?  Maybe from the hard drive? Be careful with your ear. :-)

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When I stick my ear near the CRT neck on power switch flip, I hear the tube charging, and the chirp almost sounds like it's near the fan but I can't be sure. When I first got the machine,  the ground strap was out of place and occasionally would arc on a regulator heatsink.

 

I have also attached an imgur link to pics of the 575 board. http://imgur.com/gallery/ZetALXt (Had issues with site upload) I will say, I have cleaned around the caps with contact cleaner and some isopropanol, however they are the original board caps contrary to what I was told by the seller. No one can solder that perfectly. Once I get some serious down time I can also post pics of the analog board, but I would have to remove it again. I did try and touch up and cold solder joints, and saw nothing bridged prior to re-installation.

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That noise you hear when flipping the switch is the monitor degaussing.  I'm a bit concerned by the ground strap not being connected though.  Out of the many CCs I've had the only one that didn't have the ground strap connected properly was one that the previous owner had attempted to turn into a Takky but did a fantastically bad job of it.  It's not something that likely to just come loose in shipping, no matter how rough of a ride it took.

 

If you have the motherboard out of the machine and flip the power switch does the fan kick on?  If you've added a hard drive, that should also spin up.  The only time I've heard chirping from a CC analog board was when it was already dead and wouldn't fire up with a known good board.  The power light on the front also lit up every time the analog board chirped.  Of the machines I had with that problem, most would do it three times and give up, and one would keep trying until I turned the switch off again.

 

Was this a machine you picked up on eBay?  I'd get in touch with the seller if you haven't already. 

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In my opinion, your problem is on the LB side, not Analog.

 

The logic board looks fine, but not easy to see.

 

The only strange behavior is that chirping with the LB removed, as EvilCapitalist is stating, the fan should kick on.

 

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Ok, so I did some reading on an old thread, and I had the analog board out. I removed the metal shield carefully, and reinstalled it. Now, it beeps once and the green light blinks. I currently have it plugged in letting it sit for a couple days to see if it comes up.

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