Put a power supply with the wrong polarity into a Genesis 2...now it won't turn on

[livingonwheels]

I accidentally used a power supply with the wrong polarity with a Sega Genesis 2. Now when using the correct power supply, it will not turn on, and the red power light on the console doesn't turn on either. The official Sega Genesis 2 power supply will turn VERY hot now when it's inserted into the Genesis (whether it's off or on, I think). The power brick itself, as well as the cord gets quite hot. Console motherboard near the power supply input gets hot too. The official power supply "might" be damaged now too, due to trying it with the damaged Genesis. Seems to still be getting hot, even without being connected to the console (was fine before). Reluctant to test the power supply with another Genesis 2, just in case I broke the power supply as well as the Genesis (I unplugged the power supply from the wall for 10 minutes and it's still warm). Any idea what part needs to be replaced in the console? I see no damage on either side of the board (physical inspection).

Edited May 30, 2022 by livingonwheels

[Tanooki]

You could need to swap a fuse or something of the sort, same with the power brick if you can get it cracked open safely.  I think that would be the best case scenario, likely you fried the hell out of it, not just from the first point of foul up, but then doing more after the fact having it roast itself into a heated fit.

[+H454]

I don't think the genesis has a fuse - just a power regulator.

If the ac adapter is getting hot - then the genesis is drawing power.

Most likely to much power because a component shorted.

Testing the power supply voltage and power regulator on the main board would be a go start.

https://console5.com/store/7805-l78s05cv-high-output-2a-5v-voltage-regulator-3-pin-to-220-5v.html

[livingonwheels]

Upon further testing the power supply appears to be working normally. I suppose it had become so hot while plugged into the damaged console that it took nearly a half hour to cool down. By itself it no longer gets hot and I get a voltage reading of 13.65 volts which I presume is in a safe range.

[+-^CrossBow^-]

6 hours ago, livingonwheels said:

Upon further testing the power supply appears to be working normally. I suppose it had become so hot while plugged into the damaged console that it took nearly a half hour to cool down. By itself it no longer gets hot and I get a voltage reading of 13.65 volts which I presume is in a safe range.

Yes that is a normal output voltage without a load so it seems the PSU is likely okay.

 

[livingonwheels]

Changing the voltage regulator didn't solve the issue (though I do believe  the voltage regular was damaged and needed to be replaced). Still no power light, and any power supply gets really hot while plugged into the unit. There is a chip marked "77" that is near the power jack which is getting extremely hot. I think I need to replace that chip, if I can find one.

 

Edited June 16, 2022 by livingonwheels

[Bruce Tomlin]

You better check a schematic. That looks like a ferrite bead, and if that's getting hot, something is pulling a lot of power through it. Reverse voltage, especially for more than a second or two, can easily fry a chip, which then can become a nice little heater. It looks like there are some inline diodes on the original model (which I don't see in that pic) to prevent reverse polarity... except there is also something in there wired up to the brick power. More expensive equipment would put a big diode across the power terminals such that it would blow out the power supply brick or a fuse inside it instead.

 

If you're lucky, only the 7805 power regulator(s) on the board died, but that's still a lot of work. It could also fry regulator capacitors. But it's probably toast.