Galaxy Saturn (not turbo) power supply buzz/hum-Help?

[nomadradio]

Fleabay is seemingly overrun with sellers of small enclosed switchmode power supplies. Avoid the 'open chassis' versions. The metal enclosure will provide noise shielding you'll need inside a radio with a sensitive receiver.

http://www.ebay.com/itm/AC-TO-DC-12...r-LED-Strip-/323443504807?hash=item4b4ebc36a7

I don't know anything about this particular seller, but there are more where he came from.

There are two advantages to just removing the noisy transformer, rectifier filter and regulator board/transistor.

The switchmode brick supplies have an overvoltage detector that shuts it down before it can feed excess voltage to the radio. The factory supply can put 22 Volts into the radio when it breaks down.

The brick has a current-limit protection circuit. The factory power supply has a glass fuse.

Makes it less likely to fail and croak the radio. Besides, if it gives out later a replacement is cheap.

73

 

[nbsr]

A Galaxy Saturn Turbo showed up and I couldn’t walk away. I never plugged it in, removed their power supply and connected to an external one with the radio and amp fused separately, and holy crap what a radio. After a full alignment I couldn’t stop smiling.

But I have a problem!

I installed a MeanWell RSP 320-13.5 switching ps and as the pic indicates, the fuse lines here were nothing but an antenna so I did exactly as nomad did and fused the radio on the bottom and shortened the amp fuse. Decently quiet rx but not completely silent.

Put the cover on and all hell broke loose and unbearable rx noise!

Scoping the ps and man is it ugly. Tried another ps and just as ugly.

I went back to the bench ps and all is well.


I can’t walk away from the 2290s and determined to make it self contained.

What did I do wrong and what should I do to correct it?

 

[nomadradio]

I would first try a .01uf disc cap from the positive DC output to the power supply frame, leads as short as practical. Or from positive to negative, for that matter.

I'm wondering if maybe you have a short from the power supply's negative side to the radio's chassis. They are only connected by way of a handful of disc capacitors around the edge of the circuit board. If you see DC resistance under 100,000 ohms from the negative DC side to the radio's chassis, look for disc caps with lightning-surge damage.

Maybe not as bad as this one, but look for a small gouge around the edge of the part, usually with some dark scorching.

Might pay off, might not.

73