Tales from toolroom - noisy PSU

[AlbertLionheart]

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!

 

[raybay]

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.

 

[Rage_3K_Moiz]

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

 

[AlbertLionheart]

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...