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enter image description here This board is identified as a filter power switch and is in is an Akai Sampler. It connects to a switching power supply which outputs the required volts to the rest of the unit.

Intuitively, I thought the switch was only toggling the AC line from open to closed. Now that I discovered the output connecter is always live, I know the switch is only filtering the the AC line. But what exactly does that mean for the switching power supply, causing the unit itself to "turn on"?

Considering the AC line is always live, is there a benefit to this method? Versus, just using the switch to completely cut the power.

enter image description here

Official Schematic for the part.

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What is this filter switch doing to the AC line that triggers the switching power supply to function and power the rest of the unit?

It's probably switching the neutral line hence it is still disconnecting power to the device but (unfortunately) it's still leaving the live wire connected. I guess you measured the presence of live voltage with respect to the chassis or earth connection.

BTW, it's not a filter switch; it's a switch.

Considering the AC line is always live, is there a benefit to this method? Versus, just using the switch to completely cut the power.

It's switching the neutral connection and this is not ideal but it will disconnect power to the circuit.

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  • \$\begingroup\$ ahh okay. when looking for replacement parts, the supplier called it that. Thank you for your answer! \$\endgroup\$
    – allen
    Dec 6, 2020 at 13:56
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    \$\begingroup\$ @allen it could be that the switch is broken as Brian said in his comment. Or, it could be that your incoming supply has live and neutral switched over inadvertently - you measure "live" on the brown wire or blue wire? It's not a showstopper of course because any pro going inside would always check that brown is live and if it turns out that neutral is live, a little extra thought might be needed. It isn't a safety issue to the user of the equipment. But it isn't ideal. If you see live on brown it's either a design fault or as per Brian's comment. \$\endgroup\$
    – Andy aka
    Dec 6, 2020 at 14:10
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    \$\begingroup\$ @alien aha I see something now that you've added a tear-down of the circuit. The snubber capacitors across the switch contacts will transfer both live and neutral but at a high impedance. However, a high input impedance DVM will effectively measure line voltage still. Did you measure the high voltage with the orange circled connector unplugged? \$\endgroup\$
    – Andy aka
    Dec 6, 2020 at 14:43
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    \$\begingroup\$ @Andyaka OK! that makes a whole lotta sense then. I just found the schematic and wish I included it sooner. Thank you so much for your help \$\endgroup\$
    – allen
    Dec 6, 2020 at 14:46
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    \$\begingroup\$ @Andyaka and yes I did! \$\endgroup\$
    – allen
    Dec 6, 2020 at 14:48

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