My SDS200 Hum Fix

[jandlory]

Background
I purchased my radio in December 2019 and was happy to report no hum. I noticed in mid March 2020 that I started noticing the dreaded hum. I disassembled the radio to see if the factory mod was done (small plate with copper on it) and it was.

My fix
Since I had no hum when I first got the radio I figured it must be a lose or bad connection somewhere. With the radio disassembled all appeared secure, but what I did notice was the radio chassis itself appeared to have a coating on it. I removed the copper mod plate and cleaned the chassis with some emory paper where the copper mod plate makes contact. I then removed the lower panel where the speaker is mounted and noticed the same tape that is removed on the upper panel when doing the mod applied. *Note when installing the mod plate from Uniden removing the tape from the lower panel is note required. I removed the tape where the lower cover makes contact with the chassis , cleaned the chassis with emory paper the re assembled the radio. I am now back to zero hum.

 

[hiegtx]

That's similar to this:

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

 

[Kaleier1]

Static Discharge found the real cause and fix as Steve linked to above. Has to do it on mine and the hum is 100% gone. If you do it, scrape the laquer coating off gradually in layers almost like using sandpaper. If you try to scrape it off all at once you can end up damaging the copper under the laquer.

 

[darkness975]

Mine has the hum but it's very light and only can be heard in the dead of night when all else is quiet and I'm standing within about 3 feet or closer to the unit. I hope it doesn't get worse. I know there are those who can fix it for me but I'd rather not part with it, especially now with everything going on.

 

[Kaleier1]

Mine got worse to where I could hear it from 15 feet away.

 

[JATO757]

Mine has the hum but it's very light and only can be heard in the dead of night when all else is quiet and I'm standing within about 3 feet or closer to the unit. I hope it doesn't get worse. I know there are those who can fix it for me but I'd rather not part with it, especially now with everything going on.

Exactly the same as mine. Purchased it about 3 months ago.

 

[JohnDistai]

I bought one a few days ago. There's a slight hum. There's also an odd noise that sounds like a hard disk drive as it scans. Anyone else experience this?

 

[darkness975]

I bought one a few days ago. There's a slight hum. There's also an odd noise that sounds like a hard disk drive as it scans. Anyone else experience this?

Yes. I can only hear it late at night when everything else is off and I'm a couple feet from the unit but the sound is there. The "Hard Drive spinning" sound you described I believe is the same as the "Hum" if I am not mistaken. Technically what I hear is the "Hard Drive spinning" sound when it's scanning.

 

[darkness975]

Yes. I can only hear it late at night when everything else is off and I'm a couple feet from the unit but the sound is there. The "Hard Drive spinning" sound you described I believe is the same as the "Hum" if I am not mistaken. Technically what I hear is the "Hard Drive spinning" sound when it's scanning.

Now that I'm thinking more about it I think I might have been wrong with this statement. The hard drive spinning sound may not be the same as the "hum"

 

[JohnDistai]

Mine has a "hum" as well. I don't know if it is THE hum or not. It's a very light sound. Like the odd electronics sound you may hear when you first board an airplane and get across from the cockpit, especially on smaller regional flights.

 

[SteveSimpkin]

Mine has a "hum" as well. I don't know if it is THE hum or not. It's a very light sound. Like the odd electronics sound you may hear when you first board an airplane and get across from the cockpit, especially on smaller regional flights.

That is the noise that everyone calls the "hum" sound. It is really noise from the digital circuitry on the scanner that leaked into the speaker amplifier circuitry on the SDS200. Scraping the coating under the mounting screws of the main board seems to be the best solution to this issue.

 

[jonwienke]

Scraping the coating under the mounting screws of the main board seems to be the best solution to this issue.

LCD display board, not the main board.

 

[darkness975]

I thought the "hum" was like the sound heard on ScannerSchool's SDS200 unboxing video? Not the sound that sounds like a laptop hard drive spinning when the unit is scanning? Or is it?

 

[SteveSimpkin]

LCD display board, not the main board.

Yes, the LCD display board. My mistake.
The following post have pictures.

Unauthorized modification to fix hum

Thanks for taking the time to look inside your SDS200 and sharing the information. Looking inside was the least I could do, especially after seeing the pics you took of that horrible job someone did putting that ring terminal on the end of the ground wire! Thanks for all the pics you have posted.

forums.radioreference.com

Unauthorized modification to fix hum

Thanks for taking the time to look inside your SDS200 and sharing the information. Looking inside was the least I could do, especially after seeing the pics you took of that horrible job someone did putting that ring terminal on the end of the ground wire! Thanks for all the pics you have posted.

forums.radioreference.com

 

[srpawski]

My question is this: If performing Static Discharge's fix by only scraping the screw holes and not going through the soldering of the second chassis ground, should the Uniden hum mitigation part be reinstalled or should it be left out of the unit or does it not make any difference? Seems some are putting it back in and some are leaving it out.

 

[hiegtx]

My question is this: If performing Static Discharge's fix by only scraping the screw holes and not going through the soldering of the second chassis ground, should the Uniden hum mitigation part be reinstalled or should it be left out of the unit or does it not make any difference? Seems some are putting it back in and some are leaving it out.

The Uniden mitigation part tries to force a physical ground connection between the parts. The soldering of the wire to add a ground is trying to do the same. If you do Static's hum fix correctly, removing excess lacquer so that the a solid ground connection is created, then the Uniden part would not be needed, and there would also be no need to solder a ground. If you do the fix, then leaving the mitigation part in, or out, makes no difference at all.

 

[srpawski]

The Uniden mitigation part tries to force a physical ground connection between the parts. The soldering of the wire to add a ground is trying to do the same. If you do Static's hum fix correctly, removing excess lacquer so that the a solid ground connection is created, then the Uniden part would not be needed, and there would also be no need to solder a ground. If you do the fix, then leaving the mitigation part in, or out, makes no difference at all.

Nicely summed up. I didn't see where using the Uniden part would make a difference. I think I'm gonna plan on doing the screw scrapes and forget the rest. So basically the board is coated with green lacquer, and sandwiched in between the board's surface and that lacquer is the copper that we don't want to grind off, just removing the green enough to show the shiny copper with enough of each surface area so that each screw head fully makes board contact without touching lacquer and that's it, correct?

 

[JohnDistai]

I don't hear the hum very much when I use the internal speaker; it's not obvious or irritating. Putting on Bose Noise Cancelling headphones a slightly different story. With the noise cancelling off, I don't hear the hum; no problem. Instead, I hear my family (which I'd prefer to block).

When I turn the noise cancelling on (which blocks my family somewhat), the hum is quite distinct when no audio is broadcast. When audio is broadcast, the hum goes away and is replaced with a hiss. When noise cancelling is turned off, the hiss goes away.

I think my 996XT sounded better with NC headphones. Does anyone know how to get rid of the hiss while using NC headphones?

 

[JohnDistai]

If I read the fix details correctly, it seems I need a special tool to removing the display (X-Key). Is that correct?

 

[srpawski]

If I read the fix details correctly, it seems I need a special tool to removing the display (X-Key). Is that correct?

Yes, Amazon sells it, its $12.00. I ordered one in case I decide to do it as I don't get my scanner until Friday. They have two variants, but the tools are basically identically specd and are incidentally identically priced.

Amazon.com