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Old 18th May 2011, 06:59 PM   #1
JoeDJ is online now JoeDJ  United States
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Default DC adaptor effects FM reception.

I have a particular 110AC > 24v dc adaptor and eveytime I plug it in, I loose FM reception.
It does not matter if the adaptor is connected to anything or not or if I reposition the adator/antenna etc.

I have other DC adaptors plugged into the same AC circuit without any problems.
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Old 18th May 2011, 08:02 PM   #2
DF96 is offline DF96  England
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Bad EMC protection from a switch mode power supply. It is quite likely, assuming it is made in China, that the EMC components were deliberately omitted at the factory.
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Old 18th May 2011, 08:26 PM   #3
JoeDJ is online now JoeDJ  United States
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Ok, it is from China via eBay,
It's a Samsung DC PS made is Korea, probably for the Chineese market as it has as much Chineese writing on it as English.
It came with one of those cheap, tube headphone amps but, it does appear to be quality made, at least externally.

After eliminating eveything else,this is basically what I suspected.

So, how can one be assured that any given DC adaptor is EMC shielded?
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Old 18th May 2011, 09:55 PM   #4
JoeDJ is online now JoeDJ  United States
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Here's a pic of the adaptor. It looks Ok.
It's even got a US UL logo,etc but, perhaps it's actually a cheap, Chinese Bootleg?
It's model #AP04214-UV and it's marketed under various brands besides Samsung. Some have a third ground wire (as mine) and some do not.
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Last edited by JoeDJ; 18th May 2011 at 10:15 PM.
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Old 18th May 2011, 10:31 PM   #5
DF96 is offline DF96  England
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Not necessarily a bootleg. It could be genuine, but still poorly made. The well-known brands do not always check that their subcontractors are delivering what they should. UL, CE etc. markings are now meaningless. I guess it is sealed, but if you open it up you are likely to find that the PCB has provision for EMC filtering but the C's are missing and the L's are just wire links. If you are confident about working on mains-powered equipment you might be able to fix it.

I don't know any way to check for good EMC performance apart from trying it. I bought a Philips DVD player (made in China) and it created interference in a nearby radio. I took it back to the shop for a refund, then bought a Sony player instead. Also made in China, but works fine. Maybe Sony do more checking?
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Old 18th May 2011, 10:42 PM   #6
JoeDJ is online now JoeDJ  United States
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I just did as search and it seems that the ones sold the US do not have a grounding wire and teminate in a two prong plug.
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