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View topic - Reset button for Consolized Game Gear Project.

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  • Joined: 17 Dec 2012
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Reset button for Consolized Game Gear Project.
Post Posted: Mon Dec 17, 2012 7:37 pm
Hello folks! I
recently started repairing an old game gear with the aim of permanently consolizing it.

I have a work log on the Sega-16 forums!
I cant post link because im too new but if you want to take a look please head there, its a fresh thread :)

My current question is how to properly implement a rest button on the game gear?

Sure i could just have a switch that momentarily disconnects the power supply but that seems needlessly stressful to me, i though the reset was a softer process.

I found a link ( that i cant post ) for a page that is hosted right here on SMSpower with the cartridge pinout of the GG.

Seems like pin 39 on the cartridge connector is labeled Reset and its High under normal operation.
My thought Is that if i could have a button disconnect the trace leading to 39, i could use it as a reset.

Maybe that's not the proper way to do it, I wish there was a Pinout for the ASIC, maybe there is a reset function built in somewhere in the GG.

I thought this was the right forum to ask about this, if no better ideas are offered i will try as i stated and will cut pin 39 and switch it.

Thanks in advance :)
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Post Posted: Tue Dec 18, 2012 10:56 am
That signal is driven already and forcing it low will hurt something else. You need to find the Power On Reset circuit and tap into it. Where it is, I have no idea...
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Post Posted: Tue Dec 18, 2012 8:35 pm
Oh :(
Do you mean it would risk permanently damaging the hardware?
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Post Posted: Thu Dec 20, 2012 3:53 am
Well, I analyzed the circuit for the Reset in the SMS.

What the reset does on the SMS is that it grounds pin 22 of the 315-5216
The fun part is that if I look at the pinout of the I/O controller on this very site,
http://www.smspower.org/Development/IOCtrlPinouts

It says this pin is NC.
Well, not completely true as its linked to the reset and grounding it resets the SMS.

On the genesis model 1 VA3, by opposition, the reset button sends +5v on some pin of one of the ASIC.

So apparently the Reset always have something to do with one of the SEGA ASIC.
There is possibly a pin on the GG Asic that serves this purpose but i guess finding it is a lost cause without a pinout of the ASIC...
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Post Posted: Thu Dec 20, 2012 8:01 am
The reset circuit is just a resistor and a capacitor... The resistor to VCC, the capacitor to ground and the reset is the point in between.

It's acceptable to short the reset (/RST) line to ground in order to reset the console. Because you are essentially shorting out the reset capacitor, I would recommend a series resistor (maybe 220 ohms or something) to limit the momentary current through your reset switch.
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Post Posted: Thu Dec 20, 2012 7:06 pm
viletim wrote
The reset circuit is just a resistor and a capacitor... The resistor to VCC, the capacitor to ground and the reset is the point in between.

It's acceptable to short the reset (/RST) line to ground in order to reset the console. Because you are essentially shorting out the reset capacitor, I would recommend a series resistor (maybe 220 ohms or something) to limit the momentary current through your reset switch.


Thanks for this!
Did you follow the Pin 39 trace and found these components?
I tried to follow the trace but lost it under the ASIC.
Im using a 1 ASIC VA1 837-9024 board by the way.

Or maybe this is a standard way of doing a reset on any kind of circuit?
Sry if I ask alot of questions im trying to learn stuff as im doing this.

I will try grounding pin 39 via a 220 ohm resistor.
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Post Posted: Sat Dec 22, 2012 3:08 am
Just wondering, are there any known Game Gear games that retain their SMS counterpart's use of the Pause feature?
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Post Posted: Sun Dec 23, 2012 5:55 am
I swear, this thing is annoying me to the Utmost.
I tried a few things but im working half blind.

I tried shorting pin 39 to ground using a resistor as recommended by viletim but It does not work unless i used something lower than 100 ohm. Otherwise the voltage drop is not big enough.

I touch only the contacts for a split second and it Does reset if i get the resistance low enough but then the audio glitches horribly during the bios screen. It gets normal after the bios screen though.

I actually tried shorting pin 39 directly to ground for the fastest split second and it reseted without glitch.

But because i do not know where trace to pin 39 comes from, this might be a good way of putting unwanted current strain on some component and frying the damn GG.

To limit the amount of exposure to potentially damaging current on some part, I added a 10 uf cap ( negative to ground ) and touched pin 39 to the positive lead, to get only a very short voltage drop spike. It works but i still have the audio glitching.

I guess I really need to find out where Pin 39 connects to...

I might be better off using a cap and resistor circuit to make a short voltage drop directly the whole 5v rail, instead of doing what i was just doing... I think it might actually be safer and would basically reset everything. But then that is actually what i was trying to avoid, using brute force. My objective was to find the softest way of reseting the machine. This poor GG has suffered enough already.

Edit: Ok I found where pin 39 goes, its connected directly to the ASIC, I aint touching this thing anymore, I guess im lucky i did not break anything yet by shorting this pin.

I will try this tomorrow. Start up with 10 uf C1 and 220 ohm R1. R2 is just for discharging the cap so ill fine tune it.

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Post Posted: Sun Dec 23, 2012 9:55 am
If you're going that far, why not just push-to-break the 5V line?
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Post Posted: Sun Dec 23, 2012 4:25 pm
Because i want to see how the system will react to it before starting cutting traces or wires on my board. Initially i wanted to simply cut and switch the lead to pin 39. But TmEE told me it was unsafe. Somehow im thinking he may have misread what i intended. But anyway, I may still end up trying that.

ALSO, in the meantime I found out that the game genie seems to have the ability to soft reset games. Im tempted to buy one for cheap on ebay just to see If i can find out how it works.
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Post Posted: Sun Dec 23, 2012 4:31 pm
The Action Replay does it too.

For the consolisation, is the power coming in to the AC adaptor jack or are you going to wire between a jack and the board? If the latter then you can switch in there.
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Post Posted: Sun Dec 23, 2012 7:40 pm
For now im using the powerboard as is but not sure how it will end up, there will likely be some improvisation with the case design.

If you'd like to see what ive been doing so far there is a Work log on Sega-16. Thanks alot for the ideas :)
http://www.sega-16.com/forum/showthread.php?22763-Let-s-consolize-and-old-dirty-broken-Game-Gear-found-in-the-trash


The action replay looks harder to find than the Game genie.
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Post Posted: Mon Dec 24, 2012 11:23 am
MaxWar wrote

I tried shorting pin 39 to ground using a resistor as recommended by viletim but It does not work unless i used something lower than 100 ohm. Otherwise the voltage drop is not big enough.


Forget about what I wrote. For some reason I thought you were asking about the reset circuit in a Master System. I should pay more attention...

Anyway, I used a DSO to take a look at my Game Gear's reset pulse. It comes up with the 5V rail then about 10ms later it goes low for about 2ms then high again. The edges are very of the pulse are sharp so this is definitely a logic output, not open collector. I think it exists solely to reset cartridge hardware because there doesn't appear to be anything inside a 1 ASIC Game Gear that would require a reset. From the look of it I'd say the timing comes from counting crystal oscillator pulses, not an external RC. No way to safely reset the console by playing with this signal...

I think Maxim's idea would be the easiest to implement. You could just put a normally closed pushbutton in series with the power switch. Guaranteed to work safely.
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