Fixing a SEGA Master System help!

[toploaderleo]

So yea, a few years back I tried to power my SEGA Master System with an NES Power supply and blew it. Sooooo since then I havnt been so stupid and also I wasnt in a good state of mind that day. So years later Ive decided to try in fix it (after not finding another one for dirt cheap) But I really have no idea what could be wrong with it. So far Im going over each connection with a continuity tester seeing if I blew a certain thing. Anyone know what I probably blew? Just to help me along.

[toploaderleo]

Could it be the transistor?

[Tokimemofan]

Check any Voltage regulators and fuses. You basically reverse biased the circuit. It may be fixable but I doubt if it is if it isn't one of the above.

[toploaderleo]

Any idea what an equivalent would be to the transistor? its says 73058 642K on it

[jb143]

The power supply section should be at the left side of the board (under the power jack...and possibly covered by a metal shield?). More than likely the voltage regulator blew(the larger 3 legged black part with a metal tab). The pins should also be labeled ICO. I is "In", C is "Common", and O is "Out". If you put a voltmeter across O and ground you should get 5 Volts. You can replace it with a 7805 Voltage Regulator you can get at Radio Shack.

Other things to test are the inductors JV and JG, they should each have a bit of resistance. You might even get away with using just a continuity tester...I'm not sure. Check all the electrolytic caps(the round cylinder parts). If they look bulged on the top then they're toast. Other culprits could be diodes in the power section.

I hope this gets you started.

Edit...didn't see your last post. That's the regulator. It's just a standard 7805 5 Volt regulator. Extremely common part.

[toploaderleo]

Cool Im gonna go to radioshack tonight & pick up a 7805 then. thanks! I need to replace it anyway, it snapped off the minute I started messing with it.

[fahlim003]

It's most likely the regulator. Seems to be a common issue if the system isn't working.

http://www.digitpress.com/forum/show...-Master-System

Thankfully it's a cheap and easy fix. Best of success on the repair.

[Tokimemofan]

Cool Im gonna go to radioshack tonight & pick up a 7805 then. thanks! I need to replace it anyway, it snapped off the minute I started messing with it.

Take a look for any scorch marks or signs of catastrophic failure, I have seen ICs where a hole was burned through it. Make sure to clean it up before putting in the replacement

[toploaderleo]

Well radioshack does carry the,m, just not in stores ' sooo Im gonna order one online. its cheap enough.

[DogP]

Really? Every Radio Shack around here has the 7805... http://www.radioshack.com/product/in...ductId=2062599 (hit find in store). I picked up a dead SMS for $1 many years ago, and it just needed a 7805.

DogP

[toploaderleo]

I got one. I put it in. & the sega logo came up. Thrilled with joy I reassembled the whole thing. Now when I turn it on, I get the green led on but no game. The screen turns black then in a few seconds it blinks then it just stays black. At first I felt a shock from the sheild so maybeit had a short I re soldered the ends checked to see if I still got a connection, I must oif the LED is going on. It feels warm so maybe it just need to cool down for the night, Im not sure. But Im going to try agian in the morning. I hope I fixed it...

[toploaderleo]

Alright tried it again still nothing. It does the same thing with or without a game, and the built in game isnt working either.

[Tokimemofan]

There was always a good chance that an IC was fried too. Over-voltage and Reverse Biasing are the 2 worst things you can do.

[toploaderleo]

Yea but wouldnt it have not gone on at all before? Because after I replaced the 7805 it turned on and I got the game to start, but after I put the shell back on it wouldnt load games anymore, just urn on.

[DogP]

You did cut the leads, right? If not, when you put the case together, you may be shorting the leads of the regulator on the metal shield. Other than that, maybe something else is causing the regulator to fry, and the new one is fried as well.

I don't think so, but the original one didn't have a mica insulator (thin clear-ish plastic looking piece usually coated with heatsink goo) between the regulator and the large metal heatsink, right? If it did, you need to make sure you use that on the new one.

DogP

[APE992]

Hopefully you only fried the 7805 you just installed.

[Gameguy]

Alright tried it again still nothing. It does the same thing with or without a game, and the built in game isnt working either.

Just wondering, what adapter are you using now? Did you get a proper Sega Master System one?

[APE992]

Just wondering, what adapter are you using now? Did you get a proper Sega Master System one?

FWIW you can use a model 1 Genesis adapter but as I found out as a kid doing it too often will cause the connector to break the solder joint away from the PCB trace. Thankfully it was easily fixed by adding a wire and some epoxy but still not a good idea.

[toploaderleo]

Oh yea I have the original Sega Master System AC adapter. I was hoping all I had to do was replace the new 7805, I guess I couldve shorted it out cause I did cut the pins on the 7805 but I may not have cut them enough the 1st time, so i guess Ill go back to radio shack & buy a new one and hook that one up. I just wasn't sure if I had or not since the LED was still lighting up.

[jb143]

Oh yea I have the original Sega Master System AC adapter. I was hoping all I had to do was replace the new 7805, I guess I couldve shorted it out cause I did cut the pins on the 7805 but I may not have cut them enough the 1st time, so i guess Ill go back to radio shack & buy a new one and hook that one up. I just wasn't sure if I had or not since the LED was still lighting up.

Do you have a volt meter? Because we could walk you through some troubleshooting. And would you mind taking a high res picture of the board? Also, did you take it back apart and see if it worked again that way?

The LED means that power is getting to the LED...which is a good thing...but doesn't mean much as far as the rest of the components are concerned. The regulator(I'm assuming) getting hot usually means that something (like a short) is pulling too much power.