The Palstar PS-30M (also called the Morning star PS-30M and the Manson EP-925) is a great PSU. Rock solid, heavy built and, most important for radio users, its a linear power supply which means it’s nice a quiet RF wise unlike most switch mode PSU’s that make a lot of noise on the HF bands.

It’s a shame then that its so loud when the cooling fan kicks in. The problem is that the cooling fan is idle most of the time. At low current draw this is fine as the natural airflow removes the heat but start drawing 10A, the PSU gets hot and the fan comes on at full speed.

What about if you could keep the fan on all of the time at a low speed to encourage air circulation and, at the same time, allow it to ramp up to full speed if/when it was needed? This should keep the PSU quieter for longer and maybe even stop the need for the fan to run at full speed.

This mod is easy but, as always…

Read the disclaimer!

Ok, you will need a cross head screwdriver, a soldering iorn and a 1K resister.

First, unplug the PSU and take it to the work bench. Leave it to sit for a few hours (I left mine overnight) to allow any charge left in the capacitors to drain.

Remove the top cover by undoing the screws and lift off. There is a small earth lead attached to the top cover with a spade connector. Pull it off. Now locate the thermistor that controls the fan. It is a 2 pin device that is screwed to the heatsink just behind the volt meter. It is normally closed which keeps the fan off and goes open circuit when it gets hot.

Next, de-solder one of the wires and place a 1K resistor in series. I used a 0.75w resistor and 1K gave a nice fan speed with no noise.

Put the top cover back on and test. You should now find that the fan is running all of the time. I have been using mine for a few hours now and the fan has not gone to full speed once.

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