Is it normal to get "electrocuted" from SCART cable connected to TV?

[mkl]

I used a a scart cable that actually has the shield metal connected between ends.
When disconnecting the cable from A600 motherboard with D23 to SCART adapter I touched the modulator and also the scart shield and got voltage. AC I think.
The Amiga was powered down, but maybe not the LCD TV.
I don't want to try if the same happens when TV power is soft switched off, when the ready light is on.
By the way, connecting fast blanking (RGB select) and 4:3 select signals makes the TV turn on when Amiga is turned on.

 

[mkl]

TV has 2 wire power, and Amiga PSU has also the ground. Connected to same extension lead.

When the TV has antenna lead lead to socket in another room (!):

TV power on, or soft off, same results:

Antenna connected:
Voltage between Amiga PSU shield ground and SCART shield is
213 VAC, current between 0.7 mA AC!

When antenna lead disconnected, 100 VAC 0.03 mA AC. Some ot this maybe due to X and Y capacitors in PSUs.

(Measurements voltages between grounds, currents short circuit between different grounds)
-----
EDIT: I will look if there Is an isolation transformer for antenna signal, and if it would make anything safer.

 

[miggymad]

You might have accidently grounded pin 8 of the RGB/SCART cable. That carries 12v for the AV control .

You can check this by recreating the incident, using a multi-meter and not your fingers this time

 

[mkl]

I have pin 8 connected to Amiga 12V via 1 kohm resistor, and it seems to work as in your picture states: "Brings TV out of sleep."
Newest version of the SCART adapter has a jumper for this signal, so it could be left unused.


I have some PCB:s for the adapter, but maybe I don't sell them because at worst these may be dangerous.

 

[mkl]

Lot of noise was coming from the speakers when this was tested, according to an ePanorama page, hum can be caused from TV antenna connection when TV is used with a computer.

The A600 mainboard had capacitor leak damage and was recently recapped, but it had problems, like the 555 ketboard/power on reset circuit was not working due to trace disconnected from pad.
(Not only that, Amiga failed to boot many times, I found now that the chipset _RST driven by Gayle was only 3.6V. Trace to pull-up R951B was eaten away next to Paula pad.)

Other strange thing was that while it booted from CF card, attaching an external GOTEK with an empty formatted Amiga disk image, made the Amiga crash to halt when it seeked the disk.

Edit. More to rant: The rev1.3 board has a negative voltage VBB pin 40 agnus, but R121 connects it to chip ram expansion slot as if it were 14 MHz output, of an (older) A600 agnus. VBB needs 100 nF to ground, and 121C maybe for that actually. But the signal doesn't need to go to the chip expansion.
Schematics suggest that Gayle may have 14MHz clock, but 7MHz is actually connected.
link: https://www.amibay.com/threads/amiga-fat-agnus-2mb-chip.116313/

 

[mkl]

More missleads.
The cheap SCART cables actually have shield ground, but because it is loosy goosy pressure fitted to the metal, continuity meter didn't beep.

External flashfloppy Gotek doesn't crash A600 anymore, connecting the pull-up to floating _RST fixed it? Also the noise is gone.

 

[Watson]

No, it's not normal or common to be "electrocuted" by a scart. I have made up many cables and never experienced as such but, buying cheap cable, I guess anything is possible.

 

[mkl]

The better SCART cable without intermittent shield ground connection, revealed the issue with grounding in the apartment:
The wall power outlets don't have grounds in the rooms, and the antenna voltage is whatever, maybe grounded somehow or picking voltages from TV:s in the antenna network, or I don't know.

I made a temporary galvanic isolator for the antenna with 500 volt capacitors. The cable ties didn't hold the cables enough, but the thing is wrapped in lots of tape now. I'm going to make an isolator with PCB and plastic box later.

 

[eisdielenbiker]

If you have a non-grounded PSU in the setup it is somehow normal to have higher DC-voltages on plug shieldings:
"Common Mode Voltage"

I have marked my USB-Powerplugs with the DC voltage reading measured against a good known earth from the wall socket.
And I avoid using these highly rated PSU-USB-Plugs with sensitive devices. Some are as high as 30...70 Volts at worst.
On using batteries you miss the problem especially with laptops or notebooks you connect to homebrew or old appliances.

There has always been a very small lightning when connecting to HDMI ports on my TV til I noticed this.

 

[Buzzfuzz]

TV has 2 wire power, and Amiga PSU has also the ground. Connected to same extension lead.

The TV grounds it self trough the leads, this is because it has no ground itself if it only has live and neutral, if it's grounded it would have 3 wires, so live, neutral and ground and plug with ground (colors: brown/blue/yellow-green)
This is why that voltage is running over the leads, it's common that the the antenna lead, usually cable device / modem connected, the primary cable socket needs to be grounded.

 

[kyle_b]

This is quite an old thread but 213V in AC on the SCART ground when RF cable is plugged in = that cable has AC on it's shield conductor.

This points to isolation failure in whatever is at the other end of that cable. If it's an amplifier for your own rooftop antenna then you must throw that thing away and buy a new one. If It's from Cable TV service then you have to call them and explain.