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Tales from toolroom - noisy PSU

By AlbertLionheart
Oct 15, 2009
  1. Not noise in the usual sense, but radio noise.
    A system I supplied about 6 months ago has worked perfectly (as mine all do!) and was still apparently innocent of any sin until a radio ham next door complained about excessive radio interference between 7mhz and 28mhz, and had triangulated the source to my machine.
    I fitted a replacement PSU and the noise disappeared at once - and I then tested it by connecting a PSU tester to it and reconnecting it right next to the short wave receiver. Fault confirmed.
    The whinger then pointed out that his wife was a JP and clearly expected me to run away - not so because I then asked him to pay for the repair on the grounds that his radio equipment might be faulty.
    We agreed that I would pass it to the local Trading Standards office for them to check if it conforms to permitted emissions.
    We will see!
  2. raybay

    raybay TS Evangelist Posts: 7,241   +10

    Not an uncommon problem. Your power supply will be found at fault, most likely.
    We have found that a great number of power supplies have fake UL and other clearance codes.
    As a broadcast engineer, I can tell you that it is rare that an approved design will cause any interference...
    I don't know of any tester that will find such a fault, unless you use some pretty good equipment costing $300 on up...
    Bottom line: Regulations say you cannot cause intereference to a radio signal. If your equipment is bad, you will be asked to do something about it.
  3. Rage_3K_Moiz

    Rage_3K_Moiz Sith Lord Posts: 5,443   +36

    I think it's probably because of sub-par filtering; the caps are probably failing and causing harmonics to leak out.
  4. AlbertLionheart

    AlbertLionheart TechSpot Chancellor Topic Starter Posts: 2,026

    It is almost certainly the filters - I have a suspicion that they are not there at all as I think I can see the vacant joints for them! I am not going to take off the warranty stickers yet though...
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