PS-30M PSU mod

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.

59 Replies to “PS-30M PSU mod”

  1. Sorry to hear you are having problems. I can only speak as I find. Other than the noisy fan on my Manson EP925, which was cured by the resistor modification, I’ve had no problems at all & the PSU handles the 100w from my radio without any issues.

  2. My fan was very noisy and bugged me, did the resister mod but of course it was just as noisy when transmitting and stayed on for a while on receive. Just replaced the fan with a super quiet one from Amazon, result, bliss! The fan I fitted was a 92mm ‘bequiet’ fan labelled ‘pure wings 2’. I checked the sound level of both fans, (freestanding on the bench) and the new one is about 20db quieter!
    BTW, allow a couple of hours for the job, and check carefully the wiring of the fan as it has 3 wires, center one is + , of the other two one is the – and the other is speed sensor. 73s

  3. On the Nevada PS-30M. Carried out mod ( 50 ohm 1W resistor) across the temp control thermistor as suggested by Tim M0TGY. Works a treat . Fan running slowly continuously, noise now barley perceptible. Has been on all evening running a Kenwood TS-590SG.
    Great mod. Thank you Tim.

  4. Hello,
    I have a Manson EP-925 and also a Manson EP-603 both of which have been ‘repaired’ by a so called expert at considerable cost.
    Both of them work and provide almost their rated voltage and current however the 925 is only producing about 12.5 volts and the 603 voltage regulation is far from correct. Please could you advise me of a person or company that are really familiar with these items so that I can get them back to good condition. I myself am 81 and past my sell by date and am not really capable
    Help appreciated
    Peter (2W0HOH)

  5. I’m sorry Peter, I do all my own repairs so don’t know anyone who I could recommend.

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