PSU over 100v to chassis

Thread Starter

H_L

Joined Apr 30, 2023
3
Anyone have any ideas on what could be causing over 100v going to chassis and that causing a tingle when touching the device?
I've just pulled the PSU out, haven't had the chance to check "chassis" caps or anything yet.
Cheers

Board 20230429_232139.jpg
board.jpg
 

Ian0

Joined Aug 7, 2020
10,002
It seems as though the connection between GND and the chassis earth is missing. You are probably measuring it with a very high impedance meter.
With no ground connection the secondary 0V connection of a flyback converter will tend to float to half supply (but at a very high impedance)
 

ronsimpson

Joined Oct 7, 2019
3,131
Top left corner of schematic; that point is normally connected to green wire ground.
Is the 100V AC or DC?
The three capacitors you have marked with green are "power line" capacitors. They may say "250V" but don't just get any 250V cap. These are built for 250VAC power line. They will probably hold 1000V DC.
 

Thread Starter

H_L

Joined Apr 30, 2023
3
Thanks so much for your replies.
Yes top left point (st371) is screwed onto the chassis.
I have some of the exact same caps in my draw, if they need replacing.
It's 240V AC input with no ground (so the case is not grounded thus labeled as double insulated)
Yes over 100V AC from the chassis to the grounding of my house causing a tingle when you touch the chassis.
 

ronsimpson

Joined Oct 7, 2019
3,131
I placed 1000pF caps across 220V 60hz and with a high impedance meter read 100V ac.
There is 40uA in the caps.
I shorted to ground and I get 80uA current to ground.
My mental math is close.
The supply was designed to connect to ground. It is not and that needs fixing.
It makes RF noise the way things are connected. The noise filter is not working.
 

Thread Starter

H_L

Joined Apr 30, 2023
3
I placed 1000pF caps across 220V 60hz and with a high impedance meter read 100V ac.
There is 40uA in the caps.
I shorted to ground and I get 80uA current to ground.
My mental math is close.
The supply was designed to connect to ground. It is not and that needs fixing.
It makes RF noise the way things are connected. The noise filter is not working.
I know right it puzzled me, I've worked on heaps of PSU units, even ones that have voltage on the chassis but that's was easily fixed. I'm thinking it relies on grounding through other devices through the audio/data connections as all the HDMI/RCA etc.... are connected to chassis maybe??

Had an LED video wall PSU modual that the caps from 240V AC Active to Chassis where faulty and leaked voltage to chassis causing a shock when touched, replaced the caps and no shock :)
 
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