HDMI shock - Page 1
Forum section: electronics / beginners

author: fyrewurx
author_rank: Contributor
timestamp: June 15, 2017, 01:53:11 pm
content: Hi everyone,Sometimes when you touch the shield of the HDMI it shocks you.The attached schematic is the input filtering stage of a generic SMPS.Is the voltage between C2 and C3 (half the mains voltage) responsible for this shock via the connection shoddily highlighted using MsPaint?If that point is properly earthed then the current should go trough the low impedance path to ground and not trough you so no shock right?I googled this and people only say that you need proper earthing, not what causes this.Regards,Alex

author: tszaboo
author_rank: Super Contributor
timestamp: June 15, 2017, 01:59:31 pm
content: Yes, that is responsible. These capacitors are supposed to be connected between a solid ground (shield) and parts of the SMPS, so any high frequency noise is "lost" in them. Hovewer, if you dont have proper ground connection, then they act like a capacitive voltage divider, sometimes driving your device's metal parts to half mains voltage.

author: Jeroen3
author_rank: Super Contributor
timestamp: June 15, 2017, 02:00:01 pm
content: Yes, this causes it. It's a capacitive voltage divider. The capacitors are there to comply with EMI regulations filtering noise.You should get proper grounding.

author: fyrewurx
author_rank: Contributor
timestamp: June 15, 2017, 02:13:18 pm
content: Thank you very much for the quick reply.Also when you connect to the monitor/tv sometimes there is a spark. Could that discharge easily damage a converter chip from display port to HDMI adapter? A friend of mine gave me 3 adapters that simply stopped working. Opened them up, buzzed the wires all good. There is a 48 pin chip with no marking but i believe it's a MAX9406 based on package, number of pins and function. Having no marking makes me think that it's a clone and maybe they skipped some ESD protection?While using these the TV was also disconnecting and reconnecting when he turned on the lights or plugging some devices to mains. The TV was connected to the PC.Regards,Alex

author: JanJansen
author_rank: Frequent Contributor
timestamp: June 15, 2017, 02:23:18 pm
content: Wait : are TV`s unsafe to plug HDMI cable without the TV connected to a grounded power ?In Holland only new houses have earth, most dont.Thats why they advice to power off when changing cables ?, good to know, i,m very supprised : half mains tru HDMI ground.

author: Jeroen3
author_rank: Super Contributor
timestamp: June 15, 2017, 02:29:02 pm
content: It's only unsafe for humans when the capacitors fail. The capacitors are a special safety class, X or Y class. Designed to not fail-short.It is only dangerous to devices when the connector chassis (ground) does not properly balance the voltages. Since all connectors on a TV (except 3.5mm audio) connect chassis first before the signals, there should be no damage.Also, some devices don't have ground but do have the capacitors. TV's with aC-type plugare among them, but also some laptops and phone chargers.

author: tszaboo
author_rank: Super Contributor
timestamp: June 15, 2017, 03:43:10 pm
content: It is safe for humans. Maybe it might be a problem for someone with heart condition left handed plugging in a TV in a bathroom standing in the water holding a can of gasoline.

author: ConKbot
author_rank: Super Contributor
timestamp: June 15, 2017, 11:58:31 pm
content: I had issues with an MHL adapter for my Galaxy S3 also. Plug the MHL adapter into the TV HDMI and a charger, and plug the phone in, and every time I'd pick up the phone to muck with it, I'd get one heck of a static discharge to the exposed part of the MHL/USB connector(Not a 1/2 mains leakage tingle!). No similar discharge between the me end of the HDMI cable when it was unplugged, or the end of the USB charge cord when it was unplugged. No way to explain it, as the TV was also plugged into a full size desktop PC with a 3-lead mains cable, so it was mains earth referenced, and I didn't get a shock off of the PC case.

author: Kjelt
author_rank: Super Contributor
timestamp: June 16, 2017, 07:12:20 am
content: I know this issue from a long time ago, my Pioneer Laserdisc player has such an input filter , is not grounded (c plug) and if I connect S-VHS and audio Cinch to my modern AV processor/preamplifier it causes hum in the audio.This is probably because the audio ground or mass or how you want to call it is connected in some way to the HDMI / S-VHS video ground/mass and these kind of voltages can cause interference in some equipment.So if I get this correctly grounding (mains earth ground) the point between the balancing capacitors would solve the issue ?

author: tszaboo
author_rank: Super Contributor
timestamp: June 16, 2017, 09:08:44 am
content: Yes, it would. If you connect your TV/Home Theater system to any properly grounded equipment, the problem is gone. I have my TV connected to a PC with a HDMI, that takes care of the problem for me.Quote from: ConKbot on June 15, 2017, 11:58:31 pmThat is strange indeed. Maybe it is your floor, or carped charging you when you go there?

author: langwadt
author_rank: Super Contributor
timestamp: June 16, 2017, 09:54:56 am
content: Quote from: Jeroen3 on June 15, 2017, 02:29:02 pmI'm sure plenty of soundcards have died from connecting an ungrounded PC to a TV grounded via the antenna cable

author: Kjelt
author_rank: Super Contributor
timestamp: June 16, 2017, 09:55:32 am
content: Hmmm yeah none of my consumer audio equipment is grounded, that always surprised me but that is how it is.So I would rather than ground the rest of the installation take care of the culprit being the laserdisc player.Thanks, I am going to check where to ground it then and see if this solves the issue.

author: tszaboo
author_rank: Super Contributor
timestamp: June 16, 2017, 10:06:43 am
content: Who has a laserdisc player anyway?

author: tooki
author_rank: Super Contributor
timestamp: June 16, 2017, 10:22:01 am
content: Quote from: NANDBlog on June 16, 2017, 10:06:43 amTechmoan.

author: Cliff Matthews
author_rank: Unknown
timestamp: June 16, 2017, 11:40:33 am
content: Quote from: NANDBlog onYesterdayat 10:43:10 AM

author: fyrewurx
author_rank: Contributor
timestamp: June 16, 2017, 11:56:02 am
content: Quote from: fyrewurx on June 15, 2017, 02:13:18 pmAny ideas on the above?