Mega Drive doesn't power on.

Hey guys, long time lurker, first time making an account nad posting, yadda yadda...

I bought a Sega Mega Drive (high defenition model) with no cables, and I'm not sure it works. I have a couple power supplies here at home that fit it, one that I use for my NES (9V 1A) and another random chinese one which is 12V 1A, neither of those have the exact specifications of the mega drive, but should at least power it on(right?). Anyway, I open the console up and the capacitors all seem fine, I tested the power jack and some points along the board with a multimeter and they all give me some voltage, tested some of the chips and they also gave signs of life. At this point I thought the power LED might be broken, but I tested it and it lit up fine.
I must admit, my multimeter isn't the most reliable thing in the world, and I'm not even sure if I'm using it correctly. So, anyone have any ideas/advice?

 

what ever you do don't use ANY ac adapter that outputs AC. if you plugged the NES ac adapter into it, there may be some damageas it outputs 9v AC!!!!! only use 9-12v DC!!! and make sure the plug is center negative.

 

Both of the adapters output DC, I checked that before I plugged anything in, but now that you mention the center on both is negative, I never even remembered to check, I'll see if I can find one that matches the correct specs

 

If you did pluged in the nes power back you will have blown 7805 reg.

 

The stock PSU is rated at 10v 1.2A DC. 12vDC seems like a stretch for me. I run mine at 9V DC just fine...

 

7805 can take up to 17v according to spec sheet so 12v is fine.

 

True, but as you increase the input voltage, you also increase the amount of heat the regulator produces. I'm not sure how the added heat would affect a model 1 Mega Drive, but it's not a good thing...and easily avoidable by keeping the input voltage down to Sega's original spec of 10v DC (unregulated transformer) or 9V DC (modern switching supply).

 

if i'm correct you plug in a Power Adapter then turn on the Megadrive then probe the Regulator with a Multimeter , if no voltage is being output from it the Regulator may be dead.

 

The mega drive output's 13v on my tester.

 

I hear ya on the heat that's absolutely true. shouldn't cause any damage @ 12v. 12v is the cut off for me, after that 7805 becomes a toaster.

if you have 13v coming out of leg 3, something is REALLY WRONG!!!!!!

 

I meant my official power supply output's 13v

 

um if its unregulated that may be normal. i don't have a 220v supply to compare though.

 

They are unregulated. 13V DC is normal with no load. As soon as you put the expected load on the transformer, it will drop back down to ~9-10V DC.