Gaming device potentially live case - help diagnosing needed

[B737]

ive got a gaming device that has lots of switches, servos and backlighting in it. It’s powered by 5v for main power, 5v for servos and 12v for backlighting.

It all sits in a metal case.

Just recently I’ve had a strange problem when using it that when I touch certain switches or even if I touch the metal case then my USB joystick on my pc disconnects and then reconnects. I narrowed this down to potential electrical interference (as I had disconnected everything from the gaming panel to my pc) and put 4 ferrite beads on the usb cable from joystick to pc which stopped the disconnects of the usb device when using the overhead panel but only when I used 4 x 5mm ferrite beads. The disconnects did reduce if I had 3 ferrite beads on but 4 seem to stop it all together.

This now leaves me with an overhead panel that may have a short circuit and a live case?.

My question is how do I best go about checking this with my multi meter.

I was advised to power the unit then plug one probe of the multi meter into a spare earth socket on a plug socket and then using the other probe touch the gaming metal outer panel (on a bare metal section - screw hole).

I tried this when it’s powered and got the following results when setting the multi meter to DC 2v. There was a lot of fluctuations and the range is listed below:-

All power leads connected = -1.8 to 1.8v
Just 5v main and 12v backlight = -1.5 to 0.5v
Just 12v backlight = -0.8 to 0.7v
No power = -0.3 to 0.2v

How can I have a reading when no power is connected?

Given the minus readings in the above tests I set it to AC 200v next. Here are the results:-

All power leads connected = 85
Just 5v main and 12v backlight = 83.4
Just 12v backlight = 63
No power = 20

I next tried a simple circuit test by unplugging the device and putting one probe on live plug pin and the other on neutral plug pin. My multi meter was set to circuit with audible sound. I expected to hear a sound as I complete the circuit but I didn’t? Any ideas?

The gaming device is actually fully working and functional with the exception of a couple of broken servos so in my mind the circuit tests should have worked?

Was my earth to case test even valid?

Any suggestions on how to diagnose this further?

Are the readings from above even a concern?

Thanks in advance

 

[Andy-1960]

Is this a PC type power supply that is providing the power for your gaming device?

 

[B737]

No I have 3 mains AC to DC transformers - 2x 5v and 1x12v. I can’t recall the amps on the power supplies but think the 12v is 8amps and the 5v are less at maybe 3amps.

Does this answer your question?

 

[Strima]

Does the case have an earth? You might be getting a static build up.

 

[static zap]

Where in UK are you , phantom voltages may be present ... The fix is safer with some-one who knows
simple -safe tests ! (and what Real Danger looks like)

 

[B737]

I’m in West Midlands.

I’m happy to do basic testing and checking continuity by opening it up but wanted to see what those volts were on the case and if they are real or anything to be concerned about.

 

[B737]

Does the case have an earth? You might be getting a static build up.

No. All the power connections are jack plugs which I understand don’t carry an earth and there is no earth direct from the case.

I guess I could earth it? Maybe a wire from a screw point to a plug Earth pin?

Would that work?

 

[static zap]

The volts are real in the sense you can measure them,
but if its less than a few milliamps a path to earth maybe thru a 40W incandescent lamp will provide clues ...
(Bad news... if a RCD /RCBO strips !)
Expensive transformers have electrostatic screens that should be earthed .
(are any Figure of 8 cassette recorder style plugs present)

 

[B737]

No figure 8 power leads. They are all kettle leads like would go into a normal pc psu. The kettle leads go into transformers which go to the jack plugs.

 

[static zap]

Any signs they have / are running hot .
(do with power off ..after run for a while )
Burnt smells ... can be hard to tell by colour
sadly transformers include a self heating failure mode ,
if they have been abused before ... Over heating +
Insulation failure ...
-------
A local electronics nerd may be able to measure
Total wattages / currents ...
May need supply causing most bother changing ..
Is it a commercial product?

 

[B737]

Any signs they have / are running hot .
(do with power off ..after run for a while )
Burnt smells ... can be hard to tell by colour
sadly transformers include a self heating failure mode ,
if they have been abused before ... Over heating +
Insulation failure ...
-------
A local electronics nerd may be able to measure
Total wattages / currents ...
May need supply causing most bother changing ..
Is it a commercial product?

Not running hot but do get warm. No smell of burning.

Was my test of probe to mains plug earth and other probe to the metal case a valid test?

Could it be phantom volts? How would I tell?

Would installing a wire from the case to earth in a plug and then plug it in be a good idea?

It is a commercial device but quite old now and I bought it second hand.

 

[marconi]

Sir - if you thought you had a gas leak then you would call in British Gas/Cadent with their test equipment and expertise. Similarly, since you have a possible electricity leak you would be wisest to call an electrician in to do some appropriate testing and inspection for you.

 

[Darkwood]

I would suggest that because you have several sources of power and possibly switchmode, TX rectified type or a mixture then you may be seeing floating voltages created and/or high frequency interference due to interlinking data or control cables, the generated dc may have waveform characteristics and be out of synch between devices, it is always better to source power from one device and where different voltages are needed then multi tapped outputs - this is what are used in computer towers as standard and may be the solution, this goes more into the realms of electronics tbh and not my strongest field, I have in the past seen floating voltages up to 300v that do pose a serious risk but this was from dc motor speed control unit's where the installer had failed to fit a galvanic isolator as per manufacturers instructions for a remote potentiometer which worked off 12v but floated at 208v to earth.
Are you rigging all this up yourself in a design and build format?

 

[Spoon]

It is a commercial device but quite old now and I bought it second hand

Any chance of some pics of the set-up.

 

[Wilko]

No. All the power connections are jack plugs which I understand don’t carry an earth and there is no earth direct from the case.

I guess I could earth it? Maybe a wire from a screw point to a plug Earth pin?

Would that work?

Hi - if I understand your home made device correctly, you've a metal box with connection to mains power? This box needs to be earthed, as a matter of your personal safety. Can you take a pic of the equipment ? Edit - beaten by @Spoon again

 

[B737]

It’s not home made.

Photos of the unit are attached.

It has 3 x jack plugs therefore I assume they are not earthed being jack plugs however the kettle leads that plug in to the transformer have and earth pin.

Should I run a wire from the case to earth?

I’m not even sure there is a fault with it. It was purely the fact I had to put ferrite beads on to a joystick usb to stop it interfereing with the joystick. And then when I did a voltage test on the case and a probe on earth that I got readings.

 

[Lucien Nunes]

The problem is very likely to be AC earth leakage from the power supply units / adaptors. The AC voltage you are seeing between the case and earth can result from normal leakage from the in-built interference filtering, or due to a fault. Only a proper safety test including insulation and earth leakage tests will be able to determine which of these two applies. The voltage itself is not very important - much electronic gear floats up to around 120V when the case is not otherwise earthed, it has no real significance because the source of that voltage is of such high impedance, and does not in itself indicate danger. Electricians often call it 'ghost voltage' which simply means a voltage detectable on something that is more or less floating from earth, where the leakage current is so small it's trivial and may be impossible to measure consistently.

If the DC outputs of the power supply units are NOT internally earthed (i.e. they are isolated, a.k.a. floating), and what you are seeing on the case of the device is nuisance leakage that cannot at the moment escape to earth, you could eliminate it by earthing the common DC negative terminals where they feed the electronics, and/or the case which is probably in contact with DC negatives already. If the power supplies ARE internally earth-referenced, then you have a problem with a broken earth connection somewhere in the mains power wiring because the earth connection is apparently not reaching them. You can confirm the internal earthing configuration by unplugging them from the mains, and using a multimeter on resistance to measure between the earth (centre) pin of the IEC inlet, and the negative of the DC connection to the electronics. An earth-referenced power supply will show a resistance anywhere between a fraction of an ohm to a few kilohms.

E2A the connectors you are referring to as jack plugs, which I understand are on the DC outputs of the power supplies, do not have a safety earth connection as they are for 5/12V DC. However, if the power supplies are internally earth-referenced, the earth connection is carried through the DC negative lead so although it is not present as a separate connection, anything in contact with signal & logic grounds (e.g.USB leads, the case, the internal PCB grounds) may be supposed to be at earth potential.

 

[Darkwood]

That trumps my PS4 controller

 

[B737]

So if I disconnect it from the mains and put one probe of my multi meter on Earth pin just inside the transformer and the other on the neutral pin I should get a circuit sound (bleep) and display some resistance? Will this also work if I do it on the live pin?

I guess then I repeat for the other 2 power supplies?

What will this prove? Should I see a particular reading to confirm it’s ok?

I’m struggling to know what to do next - maybe get an electrician to test it.

 

[B737]

Would you think I should Earth the case then?

If so do I simply run a single wire from the case to a plug that just has the Earth wire in it and plug it in?