What is this component?

[jeffro11]

What is this? It has 3 pins labeled QBE. I'm thinking its a switch/relay.. but... I dunno.

Q = 5v snes cartridge
B = 3v+ cr2032
E = Pin 28 and 26 of the SRAM chip.

Pin 28 however is also connected to the 5V Cartridge connector.


Now I know a minimum of 2.2 volts must be applied to the chip to retain data. I'm just wondering what this component is... Is this a switch/relay? to detect if there is 5v being applied to the SRAM/This Component so it doesn't allow the battery the power the sram along with the 5v.

I think that's what it is. Any help would be appreciated.

[Ziggy587]

I was wondering the same thing. Looks like a transistor. I've only ever seen it on the boards that use the 74LS139, so I wonder if that has anything to do with it.

I've noticed a few other "extras" on the '139 boards. There's a resistor for each chip, like normal, but then there's that group of four resistors up by the battery. What's all that about? And those two red ones with the single yellow stripe, are they even resistors? Are they diodes?

There's also a second capacitor, when there's usually just one. Anyway, I noticed this extra stuff only on '139 boards. I wonder if it has something to do with the '139 or not.

Q = 5v snes cartridge
B = 3v+ cr2032
E = Pin 28 and 26 of the SRAM chip.

We'll have to trace where those go on a MAD-1 cart, hopefully that will give us a clue what's going on.

[jeffro11]

Those are zener diodes up top.

I'm going attempt to remove this component and wire it straight through see what happens.

[jeffro11]

Ok, removed the component and the game works perfectly fine! It's not needed!

[gtmtnbiker]

Ok, removed the component and the game works perfectly fine! It's not needed!

Does the save data still work? I think you're correct that it's some sort of switch. Probably to power the SRAM with 5v when plugged into the console but then switch to the battery when it's powered off or removed from the console.

[Hobie-wan]

FWIW, I got a really messed up Mario Kart that the top left zener diode had rusted and was completely gone. Obviously the battery was toast too. The game fired up just fine without the diode being there. I have replaced the diode with a scavenged one, though haven't replaced the battery since I don't have a holder thin enough and the board fills the cart. Game seems to work fine as far as I can tell other than not saving scores though I've only played it for 10 minutes or so.

[jeffro11]

Does the save data still work?

Yes it works perfectly fine. I bridged Q to E, and bridged B to E.

[Ziggy587]

I really want to know what's up with those transistors and diodes though, and the extra cap too. Maybe Nintendo revised the carts not to use them, I've only noticed them on older carts.

[jeffro11]

Maybe, this is all we have to work from though, So I think the final design will still call for these. I may do some voltage checks later on to see why these are really needed.

[jeffro11]

Finished "mod"