I didn't get on with my switched mode power supply: it was too electrically noisy on hf. When I saw a bargain price linear power supply I quickly snapped it up. Electrically it was quiet, but after the rig had just been on receive for 30mins the cooling fan kicked in with a loud roar. A 30amp power supply making a noise like that when just feeding the rig on rx? Why??
The cooling fan stays off until the internal temperature reaches a pre-set level, then the it kicks in at full power, an 'all or nothing' cooling system. The power supply is variously named Palstar PS-30M, Morning star PS-30M & Manson EP-925. I claim no originality for the cure: there are many online sites which detail a cure, I'm simply passing on what worked for me.
There's a couple of beefy capacitors in there so I disconnected from mains power and allowed them to discharge for several hours before opening the case. I was careful not to damage the safety earth wire which connects the cover to the chassis. I did not pull the spade terminal off the cover.
When I looked at the heatsink I saw a thermistor with two solder tags: one wire was easier to access than the other so I unsoldered it and inserted a 1k resistor in series with the wire and tag. Then I replaced the cover and powered up. I noticed a gentle current of air because the fan was running slowly but continuously under low load and that was all that happened under low load. It was practically silent. Under higher loading heat built up and eventually the fan ran at full, noisy, speed as you would expect.
This was a very satisfying result for minimal effort and low cost.
Please remember to apply all necessary safety precautions; mains electricity is lethal so do not work on anything still connected to the house power supply. Stay well away from capacitors which may still carry a residual charge. Do not risk trying to find out if the fix worked by powering up while the cover is off.
Vic
