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.

51 Replies to “PS-30M PSU mod”

  1. Hi Matt
    Where did you source the resistors from and could you give me a link ?

    CPC is very close to me.

    Thanks Phil

  2. Thanks for the great how to. I’ve seen the info on the web before but I’ve never seen a proper howto.

    I’ll be having a go at this later today!

  3. I found your little mod on the Palstar PSU it ran for over an hour at 10 amps on a linear and never needed the fan to run at full speed at all. Nice not to have a Dyson turbo every ten minutes. It was beginning to get a bit irritating. Thanks.

  4. No problem. It’s not originally my mod I just wrote it up so it was clear and easy to follow.

    Glad it worked for you.


  5. Hi all,i just received a PS-30M from Nevada radio,as you all say it was hellish loud with the fan running full belt,thought there was a Chinook helicopter in my shack,lol.
    Anyway I fitted the 1.5k resistor as Matt described & the fan now ticks over nice4ly and can hardly be heard & it hardly ever kicks in full steam,many thanks for such a usefull mod,they should sell them this way from the factory,best regards,Shaun :O)

  6. Hi Shaun,

    Its amazing how much better it makes this PSU. Mine has not run the fan at full speed since I done the mod (apart from when I was testing it) and I can’t understand why they don’t do this as standard.


  7. Hi Matt,yep mate,hard to believe they ship them out of the factory like that,i made a mistake in my last message,i fitted a 1K resistor the same as you did not a 1.5k,
    anyway all good now,nice quiet shack for dx’ng,many thanks :O)

  8. hi when i de-solderd the wire the fan came on i then sloderd the resistor in line
    then the fan did not come on it was the same with both wires
    can any one help me with this
    thanks charlie

  9. sorry have put it back to how it was.
    i canot understand
    how the fan would come on when i disconnected the wire then with the resistor soldered in place the fan stops

  10. the only thing different from your picture is that i left the legs on the resistor long

  11. Hi Charlie,

    The long legs won’t make a difference and a 1K resistor is fine. First I would check that the resistor is a 1K and not a different value that has been marked wrong. Also try it with a 1.5K or 2K.

    As far as I know, this mod only works on the PS-30M model as made by Palstar and not any of the similar models/makes.

    Hope that helps.

  12. As always…



    The fan is not powered directly via the thermistor. The thermistor works like a reverse switch. When it is open circuit (like when you disconnect the wire or when it gets hot) the fan controller switches on power to the fan. That is why the fan comes on when you disconnect the wire.

    When it is closed circuit (like when the wire is in place or it is cold) the fan controller removes power from the fan.

    The problem with the PS-30M is that the thermistor only has 2 settings: fully open (fan on full speed) or fully closed (fan off). Putting a resistor in the path reduces the current and tricks the fan controller into thinking that the thermistor is slightly open so it, in turn, sends a small amount of power to the fan.

    From what you are describing, it sounds like the resistor that you are putting in circuit is not letting enough current through so the fan controller still thinks it is an open circuit.

    Ignore my previous comment and have a go at putting a very low value resistor in. If that allows the fan to spin, keep increasing the resistance until the fan is spinning and a low speed and doesn’t sound like a jet engine! It may be that you need a 500Ohm resistor instead of a 1Kohm or maybe your version of the PSU does not work like others? If it is new, maybe it has a new fan controller design?

  13. hi tried you info but had the same result no go . i have now put the psu up away from little fingers with the case off .i have had it running for 4 hr and the fan has not come on
    thanks charlie

  14. Thanks Charlie,

    That is one of the source articles that the original idea came from. There are some other mods on that page but I have not tried any of them. As I said above, the idea was not mine, I just wrote up some better instructions and images for it 🙂


  15. i just can not see why it wont work for me the pictures are the same as my psu

  16. Hello Matt , been reading your comments on the ppsu mod ,, interesting. Received my “mydel mp 925 today” Leftg it on all afternoon with no work or load for about fours hours, nice and cool as I would expect, went on the air at 50w output, and after 30 mins , woow what a blow, being as it is a Mydel fm MlS woould your mod do the trick,, I have heard of somone who just changed tyhe fan to an “Artic f8″,
    do u rekon tghat might do the trick, This should all have sorted out at the factory on”Test” , awaait your reply tks Ed

  17. Hi Ed, The problem with these PSU’s is that the fan does not kick in at all until the thermistor gets hot enough to open and turn it on. When it comes on, it does so at full blast so I doubt a different fan will help.

    The mod on this post allows the fan to spin at a low speed all of the time so the heat never builds up and the fan never has to come on at full speed and make you think a jumbo is landing on your shack! The great thing about the mod is that it will still allow the fan to kick in at full speed if needed.

    I have no idea if it will work with your PSU but its worth a try. If you can’t do this mod then maybe try and use a small 6v regulator to power the fan so that it is spinning at a low speed.

    Let me know how you get on.


  18. Hello Matt, I did the mod, things just get worse, (1.5k ) fitted. all ok until I put a load of abt 40w , and when I key or just putting the load on , the psu starts buzzing and gets worse as the load is increased, time to get another psu do u think ?

  19. Interesting. It looks like the same PSU but the internals may be different.

    How about using a small regulator to keep the fan spinning with around 5V?

  20. Evening Matt good news tried out the mod again but using a 2.2kohm 2W, and it works ok , bit chilly with fan on all the time, so re-aarranged the psu position, ontop of shelf with rig below . Tuned o/p to 100 w and nom grumbles, but I normally go out at abt 50w at the most ,,, cw only ere hi hi. So tks fer the very helpful info de Eddie 73’s

  21. I just replaced the fan with a quiet model from a high quality fan maker. Much better however i still might go down the resister route, but the internals of my PSU are different, i will post some pics on my website later.

  22. Feel free to post a link to your PSU in my comments James. I’m sure others will find it helpful.


  23. Fitted a 1.5 k resistor 2 watt and fan runs as expected very quietly and continuously .So the mod works on a brand new palstar p30 psi. So thanks Matt for publishing this on your website good mod.

    As we are all aware heat is a prime cause for electronic component failure so worth fitting for the tiny outlay and eight minutes with a soldering iron.

    All I am now still looking for is a good simple circuit to prevent over voltage (crowbar) so any suggestions would be another worthwhile addition to your excellent site Matt. Thanks.

  24. Thanks Doug.

    I’ll take a look in my junk box and see if I can find a silicon controlled rectifier to make a crowbar circuit with…


  25. Good simple engineering solution – Well done on this mod sir !
    Mines been running all day on 1K – Ive been drawing a good 10A from her for some long periods to test. The rig fans kicked in but the PSU fans remained off. Good bit of logical thinking. Cant understand why Palstar have not used a PTC/NTC type device instead of the thermostat from a tumble dryer when there’s obviously a descent voltage control circuit to the fan. Many thanks

  26. Thanks Bob.

    It’s not my idea originally. I just made it a bit easier to follow and produced an English guide.

    Glad that it helped. I can’t say that I miss the “jumbo jet at take off” noise from the fan!


  27. Hi all.

    I have the same PSU and it has worked faultless for the past 3 years.
    Yesterday the small red warning light came on.
    Any ideas folk.



  28. I’ve been using a Palstar for over a year now and the only complaint so far was from the courier who had to carry it from his van (effing ‘eavy) his words not mine !

    I get the red light syndrome whenever I switch the PSU off but not when it’s operating, so no worries there !

    I run my FT707, Wimo QRM eliminator and LDG Z100 Pro simultaneously from it and it copes famously.

    NO complaints from me.

  29. Further to my earlier post, have you any idea as to the PTT connections from the WIMO to the FT707 accessory socket as the instructions are a tad sketchy to say the least ?

  30. Thanks for this simple mod, Matt. Works perfectly.

    I found I had to swap my fan out for a new one, because it was still quite noisy, even at half speed, but it now runs silent and cool. Lovely!


  31. I recently bought a Nevada PS-30M in which both the physical layout and fan control are very different. It retains the feature of an on/off single speed fan with unacceptable noise 🙁
    The fan is powered direct from a 12V supply via a normally open temperature switch, closing (it says) at 46C.
    I by-passed the switch with a parallel pair of R56 1/2W resistors (= R28 1W) which gave 8V at the fan with a respectable air flow but a definitely audible fan hum.I haven’t managed to get the fan to full speed yet other than by shorting the switch.
    Think I might get an R50 1W pot so that I can vary the low speed setting according to TX power, mode and mood.

  32. Hi All – I did the mod on mine and it worked although the fan was still audiably loud to me. I’ve taken the mod one step further and replaced the fan with a more modern design. I’ve fitted an Artic AFACO-080P2-GBA01 low noise, high airflow fan (£3.50 ebay). This was fairly easy to do. You need to drill out the rivets on the fan cover on the rear of the supply. Remove the old fan and solder the new fan wires in place (black is earth and yellow is live – discard the blue and green wires) I used bolts to secure the new fan in place and lock-tighted them in.I found by replacing the rivets with bolts the fan was more secure to the chassis. The new fan not only now runs silent it gives greater airflow to the supply. I can’t even tell the fan is running at all now. Hope this is of help to someone.

  33. Great tutorial, although like some others, I have the EP-925 model which I purchased from Maplin. I tried putting in a 2.4k resistor and then removed it and tried a 1k resistor and the fan did not move at all on both occasions. I then put it back to its original state and replaced the fan with another quieter Maplin fan with a noise of 22.7db but this fan although quiet was only a 26.16 CFM compared to the Sunon EE80251S1-0000-A99 original fan which was 41 CFM but it’s noise level is an excruciating 33db and very hard to listen to when driving a 100w radio during a DX session.
    I have since ordered a Noctua NF-A8 PWM which is only 17.7db at full speed and has 32.67 CFM and only 2200RPM. So only a difference of 8.38 CFM and mega quiet, now I can DX without having to use my headphones although while talking I could still hear the noisy fan in the background with the headphones on which was really irritating and driving me insane to say the least. The heat sink in these PSU’s do get really hot, so the more CFM the better but I think the Noctua NF-A8 PWM is a very good compromise and £15-£20 versus another PSU costing maybe £180-£280 for a decent then I’ll stick with only having to spend £15-£20. At least I can DX for hours now and not worry about it so much:)

  34. Hi Matt, I have a Manson EP-925 PSU, only a few months old & the fan noise was driving me nuts. I carried out the mod or rather my Son M0CQG did as my hands aren’t as steady as they once were & space is limited. BINGO!The fan runs continuously at a low level & after 2 hours on both receive & a few short transmissions it’s as quiet as a mouse.Oh, the relief! Thanks again Matt for publishing the mod, much appreciated.

    73, Mike. G4MJA

  35. I have a PS-30M (Nevada). This has a thermal sensor which is normally open. When it closes it sounds like a fighter jet on re-heat. Bridging the sensor with 50 ohms allows the fan to run continuously quietly,but allows the sensor to operate normally should the temperature rise above its trip point.

  36. Looks like my Nevade PS-30m has had it after only 2 months use.The voltage is all over the place and the fan noise unbearable.It does’nt like 100w from the Icom 7400 clearly.Anyway its going back.

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