Mitigating the mitigation fix (hum)

[bobruzzo]

SDS200. I had noticed a slight "hum" at beginning, during and at end of a transmission a couple of months back. But it was not that audible unless room was VERY quiet. I got this radio back in late May. But like some people since I knew it was there it was starting to bug me. Especially on those early mornings when I was up and house totally quiet. So I read up on this problem and really didnt want to tear radio apart. So as some people reported, the "mitigation" part may have shifted position over time. But my radio was mounted right where it is since day 1 and never moved. Didnt notice this little "hum" for a while after I got radio. I don't think the hum was there from when I first got radio. I wrapped AC cable where it plugs into radio a few turns around a choke but that made no difference. Then I very slightly pressed down on top front of radio during a transmission and I noticed the hum had gone away. So I thought maybe the "mitigation" part might not have good contact. So for the heck of it I wedged in a thin piece of foam between top front of radio and the wood shelf its mounted on. The foam is firm but soft and the pressure is very minimal on radio top. Hum barely audible if at all. So I also have the audio amp turning off quicker after a transmission.

 

[Kaleier1]

I did the StaticDischage fix but before I did, I noticed the longer time setting I used for the audio amp the more of the first part of the transmission was received.

 

[bobruzzo]

I guess some people might be right about these radios (SDS) being a work in progress. Well it's sort of like Windows....Microsoft would push the executives to push the sales to get the product out before it was fully tested according to a report I read years ago. If they got the product out in accordance to this "rush" schedule., the executives would get a bonus. So all these "service packs" are just fixes for Microsofts screw ups. On the other hand it would take too long to test drive and debug an OS as large/bloated as Windows. I am not sure what the deal is with the SDS radios. But for $700 I would expect the radio to work as its supposed to. Thats why I waited a long time before buying it. I read all these horror stories about "hum" bad display issues....Who do you blame? I think Uniden has to take a closer look at both design, production, assembly......TESTING.....

 

[gunrights]

Audio hum can be a difficult thing to find it a diagnosis. I deal with it all the time here at home with different things. Some people cannot hear the frequency that I am hearing and they don't hear the hum. But it drives me crazy like nothing else. My desktop computer audio system has a hum that comes and goes. I have never been able to nail it down and when there's no audio sometimes I hear. Usually, my fixes just to mute the audio but that's not something you want to do with your scanner. So now I'm curious, Do we know if the audio hum is actually coming out of the audio output of the scanner or is it a vibration that's causing a hum like noise from components?

Has anyone hooked an oscilloscope up to the output of the scanner?

 

[kruser]

Audio hum can be a difficult thing to find it a diagnosis. I deal with it all the time here at home with different things. Some people cannot hear the frequency that I am hearing and they don't hear the hum. But it drives me crazy like nothing else. My desktop computer audio system has a hum that comes and goes. I have never been able to nail it down and when there's no audio sometimes I hear. Usually, my fixes just to mute the audio but that's not something you want to do with your scanner. So now I'm curious, Do we know if the audio hum is actually coming out of the audio output of the scanner or is it a vibration that's causing a hum like noise from components?

Has anyone hooked an oscilloscope up to the output of the scanner?

It is a hum induced by improper grounding of the display circuit board. A mechanical (vibration) or vibration (microphonic) of components were ruled out a long time ago.

SDS100/SDS200: - My SDS200 HUM fix

Here are my 2 cents on this hum issue.. I took the cover off and I do have a factory installed NMP200 so I removed it.. The hum did get much more noticeable! So I took it all apart to see what, if anything could be done and here are my findings: The NMP200 simply connects the "screen ground"...

forums.radioreference.com

SDS200 Hum > External Speaker See the picture in post 7. It shows what must be exposed to offer a proper ground that to @StaticDischarge

 

[bobruzzo]

Right. I still say better quality control is needed and more testing. This "hum" should have been found and fixed right away. The design plans for the radio obviously must have shown the need for a solid ground connection here. This shouldnt happen to a 700 dollar radio.

 

[bobruzzo]

So I took cover off radio, and I wanted to get a closer look at the mitigation part. Sure enough it was in there but contact to metal was slightly intermittent. I previously noted applying pressure to top front of radio would almost eliminate the "hum". So I simply put in a small piece of tin foil folded up right on top of the mitigation part, replaced cover and POOF. NO MORE HUM AT ALL. So apparently the mitigation part is not THICK enough to make solid continuous contact. So I have mitigated the mitigation part.

 

[buddrousa]

The mitigation part is not the fix. The fix is listed in post 5 this is a proven fix the fix in post 7 will fail again as posted by others here that tried the fix in post 7.

 

[bobruzzo]

The mitigation part is not the fix. The fix is listed in post 5 this is a proven fix the fix in post 7 will fail again as posted by others here that tried the fix in post 7.

OK I will have to look deeper into this