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Easy +3.3v Monitoring

The mainboard’s BIOS is known to report imprecise voltage values, so the best way to measure the real voltage is a multimeter attached to the Molex connector. However, this can give you the values of +5v and +12v voltages only, which are present in the 4-pin connector. While the +5VSB, -5v and -12v are not critical for the user, knowing the real voltage on the +3.3v rail is important.

This voltage is only supplied to the mainboard through the 20-pin ATX connector, but why can’t we make yet another slight adjustment to the construction of the PSU, now that we’ve got started?

Let’s return to the place where the 50Ohm resistor is soldered into the sense wire. Towards the PSU, there’s also a variable resistor, after which there goes a reduced voltage. But before the fixed resistor, the voltage in the sense wire equals the voltage the mainboard receives!

So, I solder an additional wire into the sense wire, before the fixed resistor. You may want to use a wire with a well-isolated plug on the end.

I take this wire out of the PSU, attach a multimeter and enjoy a true voltage monitoring on the +3.3v power rail.


I hope the described modification will open new opportunities for devotees of extreme overclocking, while the owners of low-power or low-quality PSUs may be able to avoid an upgrade by adjusting the voltages manually.

So, good luck with your modding experiments!

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