SMS power up woes

[Xexyz]

I'm pretty new to the Sega Master System scene so I'm looking for some help. About a month ago I purchased a used SMS from a local specialist store and after returning home, proceeded to hook it up. It worked great. Some of you might remember my post about the Genesis 1 AC adapter compatibility I posted a month ago.

Anyway, the thing worked fine, and has proceeded to work fine up until last night when I decided to test out my new AV cable. All of a sudden the system won't power on anymore. I went to hook it up last night and proceeded to power it on, but noticed the green LED didn't light up. I turned the TV and system selector on and there was no feedback. Making sure it wasn't a fried AC adapter, I tested it out on my Genesis 1, and it proceeded to power up just fine.

Is there a common power failure for SMS hardware? Do the transistors die out easily in these consoles? I mean, I had it stored in my closet for one week, and made sure the power button wasn't pressed in when I hooked it up.

What makes this even odder is that I was at a friends house earlier today, and the same thing happened to his SMS. However, he most likely fried his console due to testing it out with an NES AC adapter.

[ApolloBoy]

I've heard that the 7805 voltage regulator in the SMS causes that. I'd try replacing that first.

[omnedon]

Did you and your buddy by any chance accidentally hook your SMS's up to an NES AC adapter?

That would blow your VR, and explain the double failure.

[Frankie_Says_Relax]

I recall vividly from childhood - a friend of mine using a NES AC on a SMS and witnessing the thing output a scary "wheeeeet!" noise and then "pop!" and a small amount of smoke rising up out of the rear. Needless to say, it wouldn't power up any more either.

I've also seen blue "arcing" between the SMS AC male pin and the female slot when putting them in and taking them out, and while the units haven't "crapped out" after that, arcing electricity can't be a safe phenomenon ... I'm not sure if that's the kind of thing that may have happened to you, or if it's something to do with the AC setup ... rather the DC setup.

Sega Master Systems do not have diodes that protect against the voltage that the NES AC adapter outputs.

Take a long hard look at that "Genesis" AC adapter you're using ... is it an "official" Genesis AC (with the stylized plastic molding), or is it a "Recoton" type NES/Genesis replacement AC? That might have toasted your system.

[Xexyz]

Did you and your buddy by any chance accidentally hook your SMS's up to an NES AC adapter?

That would blow your VR, and explain the double failure.

I can't speak for the previous owner (don't know him/her), but since acquiring it, this SMS has never been powered up by an NES adaptor.

Also, I don't know if this is a problem, but in my AC adapter question from a month ago, I asked if the Genesis 1 adapter I got with the system was compatible. Yes, it is official with the Sega logo and looks just like your standard Genesis 1 adapter with the "stylized" plastic molding. But what some found odd, was that it was rated at 10V DC instead of the usual 9V. I don't know if this could be the culprit, but I'll post the adapters ratings for you guys:

Genesis 1 adapter I got with the SMS:

Model: 1602-1
Input: 120V AC 60Hz 20W
Output: 10V DC 1.2A

For reference, here's the ratings of the official AC adapter that came with my Model 1 Genesis:

Model: 1602
Input: 120V 60Hz 17W
Output: 9V DC 1.2A

EDIT: Also, there was never any smoke. It worked fine the last time I used it.

[FABombjoy]

Either power supply is fine. You need to open it up and see what's going on between the power jack & the voltage regulator (bad jack, switch, regulator, etc.)

[Xexyz]

I decided to open up the system and remove the RF shield for pictures in hopes of visual guidance. However, I will admit I'm not technically savvy. I don't see anything with the number 7805 printed on it. So before I snap a useless picture I thought I'd ask if I'll need to be taking the board apart to remove that other little shield with the screws facing the bottom of the system?

[SkiDragon]

I forget exactly, but the regulator will be a three pronged, black "chip" that sticks out, and should be screwed to a small heat sink. I will be near where the power supply plugs into. Replacing that should fix the system, but I would try to identify the source of the problem before trying it again.

http://www.opamp-electronics.com/~op...tor_012950.jpg

That is not a 7805, but it looks the same.

[Xexyz]

Thanks SkiDragon, that picture was helpful. I completely overlooked the voltage regulator the other day, but now I can see it clear as day. Getting to that screw that holds it in place isn't too hard, but taking it out without stripping the head is proving to be difficult...

If I manage to ever get that bit of RF shielding off, I might just go out and spend my money on a multimeter and a soldering iron.