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  • Joined: 26 Jan 2020
  • Posts: 6
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Master System 2 - Reset Button
Post Posted: Mon Jan 27, 2020 12:05 am
Hello,

i spend almost 3 hours on this topic but at the moment I am not sure what to do.

We have PIN 33 on 315-5237. This is the reset input. My question is because of different meanings so far:

I have to lift the pin solder a resistor between (1k5 ohm) then take a button solder it to ground and to pin 33 before the resistor

Or i have to lift pin 33 and solder it to a button connected to ground?

I want to make it right so sorry for the question. Didn't find the solution on the forum or it wasn't clear enough to me.

Best regards Alex
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  • Joined: 14 Aug 2000
  • Posts: 526
  • Location: Adelaide, Australia
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Master System 2 - Reset Button
Post Posted: Tue Jan 28, 2020 1:37 am
You will first need to work out what the pin is connected to on your console because from memory these inputs have internal pull-up resistors but some SMS2 will have these pins floating and connected to nothing, whereas some will have the pin hardwired to Vcc (5 Volts). Visually follow any traces from this pin and/or use a multi-meter to work this out. Get it right or you may cause damage when the Reset Switch shorts Vcc to ground.

If the pin is connected to nothing on your console, then your Reset Switch can be wired directly to the pin with no mods.

If the pin is hardwired to Vcc on your console, than you need to disconnect the pin from the PCB or cut the trace on the PCB before connecting your Reset Switch to the pin.

For consoles that have a Reset Button fitted, the Reset Button temporarily connects this pin to ground when the Reset Button is pressed. So the pin will be connected to one side of the installed Reset Switch, and ground will be connected to the other side of the installed Reset Switch.

If you had to disconnect the pin from Vcc and after the mod it appears as though the Reset Switch is pressed down when it isn't, assuming you have not made any mistakes in your mod, you will need to connect an external pull up resistor between the pin and Vcc along with the switch. Use a 4.7K resistor for this.

Good luck.
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  • Joined: 26 Jan 2020
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Post Posted: Tue Jan 28, 2020 7:05 am
Thanks for your detailed explanation. I think it is connected to vcc but i will check it again. I have a question about the resistor if i have to use one.

What's the technical explanation to use a 4,7k resistor. In my first post i write about a 1,5k resistor. Is this one to weak?

Best regards Alex
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  • Joined: 14 Aug 2000
  • Posts: 526
  • Location: Adelaide, Australia
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Master System 2 - Reset Button
Post Posted: Wed Jan 29, 2020 10:46 am
4.7k is a standard, rule of thumb, value for pull-up resistors for CMOS. But a value between 1k and 5k can be used.
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Post Posted: Mon Feb 03, 2020 1:39 pm
Want to share that it works fine with pin lifted and resistor between to the switch to ground. Thanks for your help! I had VCC on this Pin.
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