Repairing an AC to DC plug

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Old 05-19-10, 12:33 PM
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Repairing an AC to DC plug

Ok, so I have an old Sega Genesis plug that had died.

I opened it up and found that the capacitor inside had leaked.

So I ordered a new capacitor for it (rated the exact same 16v 3300uF)

I soldered the new one in, reassembled it, and gave the plug a test with a multimeter.

Now the rating on the plug says it should be putting out 10v DC. However, when I tested it, I get 13.89v DC out of it instead...

My Genesis says it needs the 10v, the plug says 10v output, yet I am getting 13.89v on my multimeter. Is this bad? I don't want to burn up my Genesis.

What could be happening in the plug to cause it to put out that much more voltage? All I did was replace the capacitor with one rated exactly the same. There was some leakage from the old cap. on the board, but I cleaned it up as best I could.

Is it something wrong, or would the load from the Genesis offset the extra 3v output or something that my multimeter isn't?

Thanks in advance!
 
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Old 05-19-10, 12:40 PM
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All "WALL-WART" adapters will run High while testing simply because the arent "Loaded". you should be just fine. If you are still skeptical, get a small automotive light bulb, and add it to the TEST circuit .(To simulate a Load)
That should be a little closer to what you expect.
 
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Old 05-19-10, 12:52 PM
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You should be good to go once the power supply is under load. Enjoy Road Rash and Sonic.
 
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Old 05-19-10, 12:56 PM
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Thanks a lot I'm going to go give it a try!
 
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Old 05-19-10, 02:57 PM
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Well, the plug does work, unfortunately, the Sega video is all garbled, and the sound has a buzz to it.

I've cleaned the cartridges and the pin connector inside, but nothing has changed.

I'm hoping nothing burned out when the last cap. blew.

Everything look good to the eye inside, but who knows.

I'm kind of out of ideas.

It's a shame if I can't fix it though, the games are playing and you can hear the sound behind the buzzing.

Anyone have any ideas about what would cause this?

Thanks!
 
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Old 05-19-10, 03:38 PM
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Sega website has a real good troubleshooter. That pin connector where the game fits into is a real problem area. They sell replacement kits but first I would just try inserting the game several times. Sometimes the pins get a little corroded and just need the friction from the cartridge going in and out a few times to clear up the buzzing.
 
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Old 05-26-10, 04:05 AM
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Sounds to me like you're getting excessive AC "piggy-backing" on the DC. Are there any transistor-looking thingies (three prongs, likely with a metal tab) in the power supply? If so it's probably a regulated design and should put out 10V loaded or not, and the regulator is almost certainly shorted and should be replaced. The shorted regulator is probably what burned out your cap in the first place.

Barring that, my best guess is you've got an open diode. You'll either find 4 discrete diodes or find a 4 prong package called a bridge rectifier. For discretes, they should conduct in one direction and not conduct when you reverse your probes. If you find one that doesn't conduct in either direction, it's open and should be replaced. If it's a bridge rectifier, well, uh, google "full wave bridge rectifier circuit" or similar and with some head scratching you'll be able to figure out how to test it as if it were 4 discretes: which, in fact, it is.

If you're lucky your VOM has a diode test function, if not the results of your testing can be misleading.
 
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