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gobabushka

Color Classic Analog Board Diodes

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As part of my ongoing saga with my basket case Color Classic, I took another look at the analog board and saw some burning around DL21 and DL22. At least one did not test right on a meter, so I figure it's easy to just replace them Could those cause my CC to not start up? All it does is make a click and blink the front led. I have attached a pic of the diodes in question and a video of what the computer is doing.

IMG_20190819_001712.jpg

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Certainly could do that. Uncertain if those are common failure points on a CC (I have no experience with them), but I have worked with other electronics in the past where overworked, stressed diodes will do that simply from heat. If that is the only issue (and not too much current being passed to them from another issue elsewhere), then replacing them with higher  amperage rating diodes (and raising them a bit more from the board) will help with cooling and dissipation.

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Those diodes getting hot and scorching the board is a common problem with the CC

 

I havent seen them "fail" though. But anything is possible with the age they are at now. 

 

Anyways, your issue is known as cycling. the power supply is either going into overcurrent, or overvoltage protection. If its been recapped, then your next suspect may be the opto-isolators could be bad and sending a false overcurrent or overvoltage condition to the SMPS controller. 

 

Otherwise, ohms checks on all your B+ terminals are in order. 

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I have not recapped the analog board as the caps looked good on visual inspection, and the machine was "working" when shipped from the seller lol. This may sound like a silly question, but what and where are my B+ terminals? Also what is the best way to test the opto isolators? Do you happen to know part numbers or pics so I can take a glance at the datasheets? I'm not home at the moment, but should be back in a week-ish. @techknight, I appreciate your help!

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Appreciate the input guys, ill go ahead and get some caps ordered. Does anyone have a pic of the rear side of the analog board? Just want to make sure I have something to compare it to.

 

Also, does anyone know if I can power up the logic board from a bench power supply for basic testing, such as to see if I hear the startup chime out of the headphone jack?

Edited by gobabushka

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