Hum with fast charger anomaly

[Vini darko]

Got a hum anomaly with my lg v30+ when using the fast charger.

First situation: when headphones are plugged into the phone and it's on fast charge. There is mains hum in the headphones if I'm Not holding the phone , that goes away if I'm holding the phone.

Second situation: with headphones plugged into my hifi and the phone on fast charge ( phone not connected to hifi). I'm getting mains hum if I'm holding the phone but if I'm not holding it the hum goes away.

Whats going on here?
Worth noting that this situation doesn't occur when using a normal samsung charger.
I feel like there's something to learn here as I can't figure it out.

 

[Doodski]

Perhaps the fast charger has a bad ground.

 

[Vini darko]

Perhaps the fast charger has a bad ground.

I opened the charger up. Can't see any cracked solder , corroded contacts or obviously bad components. It's cheap and nasty in there though.

 

[restorer-john]

When you say 'hum', do you mean 50Hz/100Hz or a higher frequency? Hum could be leakage via a cap to ground/0v on the USB outer. If it's higher, like a medium freq buzz- it's from the SMPS itself.

Post a pic of the internals of the charger- pcb and component side if you can.

 

[Vini darko]

When you say 'hum', do you mean 50Hz/100Hz or a higher frequency? Hum could be leakage via a cap to ground/0v on the USB outer. If it's higher, like a medium freq buzz- it's from the SMPS itself.

Post a pic of the internals of the charger- pcb and component side if you can.

Its definitely mains 50-100hz hum.

 

[Vini darko]

The charger does make mechanical noise. It sounds like a smallish fly trapped in a spiders web with little bursts of effort to escape. But none of that is audible electrically.

 

[restorer-john]

Can't see the tracks under the 6.8uF cap, but the blue cap to USB GND is coupling the 50/100Hz. These chargers are everything I hate about SMPS supplies. Safety is totally out the window. I think those two green electros may even be TEAPO brand.

 

[Vini darko]

Caps are Hyncdz branded. I'm none the wiser but suspect they are trash.

 

[restorer-john]

Caps are Hyncdz branded. I'm none the wiser but suspect they are trash.

Who knows, they may be OK. Some cool videos of cap manufacture here:

http://www.hyncdz.net/

 

[Doodski]

Who knows, they may be OK. Some cool videos of cap manufacture here:

http://www.hyncdz.net/

If the Chinese and other Asian countries/corporations keep trying and making electronic components eventually they are going to get it right. Remember when the corporations pulled the gear out of factories in Japan and reopened factories in Malaysia, Thailand, Vietnam and China etc and the QC was horrible for what appeared to be identical models to the Japanese models. They eventually ironed out the details and now they are making some of the best gear around. If there is a will they'll find the way. Plus I was reading a article years ago that explained in technology manufacturing like electronics the factory gear is replaced with new technology every few years to keep up with the progression. The article explained that factories can simply close in one location and reopen in a totally different country when it is time to upgrade the factory gear. So the closing of the article left the reader with a sense that China could actually loose it's super manufacturing capacity because if there are more economical countries in Asia to make and assemble electronics the corporations will simply move when it is time to upgrade the equipment. It's how manufacturing in the USA Canada, Europe and other places was simply moved to Asia and the same thing can happen to any country including China.

 

[AnalogSteph]

Its definitely mains 50-100hz hum.
View attachment 136831View attachment 136832

You weren't kidding about cheap and nasty. Not even an across-the-line cap (let alone anything fancy like a common-mode choke), so I can't imagine it's particularly good in terms of EMI, and primary / secondary spacing looks a bit marginal, too. Mechanical noise is something I tend to associate with marginal secondary-side electrolytics. This would be a good one to send to Big Clive for dissection...

As for your hum issue, it's likely to be the lone Y1 capacitor connecting secondary-side ground to primary-side ground (the single part aimed towards EMI reduction). According to simulation, the latter is seeing a distorted AC voltage about half the mains voltage in amplitude with a DC offset no matter L/N polarity on the plug, so you've always got a few nF coupling output ground to that. I would guess holding the phone reduces any voltage differential between it and your body compared to just having earphones in, i.e. the sneaky leakage current is then primary making its way to earth via your hand.

With you being in the UK, does the mains plug feature any PE connection? This could be used to connect a large Y class capacitor (ideally approaching 100 nF if this will even fit) coming from output ground, which would substantially reduce this issue. With it being a polarized plug, one may also consider rerouting one end of the Y1 capacitor from primary-side ground to the N(eutral) input... I'd have to think about the potential EMI implications for a minute though. It goes without saying that you'd better know what you're doing around mains voltage for this, plus there's probably not much of a point in doing this to something so marginal to begin with.