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Sega CD/Genesis inconsistent humming/ image distortion Please help me fix it

#1 User is offline RamiroR 

Posted 25 January 2015 - 03:51 PM

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Hello everybody. I have a Sega CD Model 2 and a Genesis II and they are having this weird problem and I've been trying really hard to find out what it is. So, basically, there is this humming coming from the speakers whenever the system is on, and also this image distortion/flickering.
I am using a 10V 1A DC adaptor for the Genesis, and a 9V 2A adaptor for the Sega CD. (Both generic). I should also clarify that neither the Genesis nor the Sega CD have the internal metal shields and I'm also not using the mounting plate (I didn't get it when I bought them).
I've been trying different combinations of things in order to find a pattern but I couldn't , so I'm just going to type down everything I did and what came out of it.

Using the Genesis ALONE unattached to the Sega CD: Clear audio , clear video (at least most of times, very rarely the video would also look a little flickery)

Genesis + Sega CD, both plugged, playing a SCD game: Humming and video "interference"(?) (Horizontal bars moving vertically really fast). EXCEPT sometimes! I don't know why but sometimes it works just fine!

Genesis + Sega CD, both plugged, playing a Genesis game: Same as above.

Genesis + Sega CD, only Genesis plugged: Very loud humming and significant image distortion.

I also noticed that the humming is very quiet during the TMSS screen or any other blank/black screen.

It's so frustrating not knowing where to look! I am trying to sell these consoles which is why I'm so interested in fixing them.
If anyone knows what it might be, I'd be SO grateful.
My attempts to fix the problems: cleaning the cartridge slot with a toothbrush dipped in rubbing alcohol and cleaning the expansion port with acetone.

I probably could have given more details about this or explained it better, so if something isn't clear enough, just ask.

#2 User is offline GerbilSoft 

Posted 26 January 2015 - 11:37 AM

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Could be bad capacitors in the Mega CD. You should disassemble it and look for bulging capacitors; if you find any, replace them with matching new capacitors.

...alternatively, it could be AC interference on one or both of the power supplies. You'd need to use an oscilloscope to examine the DC input lines for interference.
This post has been edited by GerbilSoft: 26 January 2015 - 11:38 AM

#3 User is offline RamiroR 

Posted 26 January 2015 - 08:25 PM

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Yes thats what I first thought of. So I opened up both consoles but capacitors seem fine (can they be bad and still have their tops flat? Ill upload some photos later). And yeah, I used to think it was the SCD's adapter (since it would happen mostly when attached to it), but now I got this new 9V 2A AC adapter and the problem persists so I can rule that one out, it might still be the genny adapter though. Is there any other way I could see if it's the AC adapter without an oscilloscope? :/

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