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I'm trying to extend a surface mount switch on a PCB. The bottom two connection points trace to ground and the top two connection points trace to ground if and only if the switch is depressed. That makes me think this is a pull-down configuration (sorry, somewhat new to electronics). Is this correct?

Will I be able to extend the switch by simply tapping any ground point and one of the top connection points to a pull-down switch?

Does anyone know of a good technique to isolate the solder point from the metal chassis of the switch so that I can solder on a tap without risking bridging over to the metal on the switch chassis? I was thinking some type of wax or something I can brush on the the switch chassis.

Here is a link to the PCB where I'm trying to trace the top two solder points for S1. I was hoping to find connectivity from one of the top solder points of S1 to U3, but I didn't find anything.

Just taking that picture enabled me to see that it flows to the top pin of S1 from the output of D2, on the bottom pin (was able to validate via the datasheet). I still want to figure out where the signal is getting processed by the IC to detect the pulldown. I was assuming it would be on U3 somewhere but I can't seem to find it.

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  • \$\begingroup\$ Wax melts at a lower temp than solder. Maybe you can isolate using kapton tape. Kapton tape is very temperature resistant and can even survive going through a reflow oven. Or just be careful not to make a bridge with solder. \$\endgroup\$ Commented Jan 26, 2023 at 0:57
  • \$\begingroup\$ Kapton tape sounds like the right solution, I will try that. thank you for taking the time to reply. \$\endgroup\$ Commented Jan 26, 2023 at 1:08

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That makes me thing this is a pulldown configuration (sorry, somewhat new to electronics). Is this correct?

For the pullup, Check the continuity to VCC (a power rail) and see if the resistance is fixed, could be somwhere from 10k to 100k normally with the switch open. Check both switch pins.

Will I be able to extend the switch by simply tapping any ground point and one of the top connection points to a pull down switch?

If it's connected to ground then yes, you can also check continuity to a known ground point, then check both switch pins.

The surest way is to solder wire from each pad of the PCB to the same pad on the switch. A good idea is to also provide a way so the switch is fixed so the wires don't break.

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  • \$\begingroup\$ > Check the continuity to VCC I checked it and there's no continuity between both top pins and VCC and there's no continuity which is what struck me as odd \$\endgroup\$ Commented Jan 26, 2023 at 0:34
  • \$\begingroup\$ added a link to images of the PCB to show what I was trying to trace. TY if you have time to engage! \$\endgroup\$ Commented Jan 26, 2023 at 0:58

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