Wierd grounding problem with laptop

Nigel Please read again.

The charger is Class II if double insulated from the grid connected bnut still needs to a primary CM filter to divert RF current to ground .

If you have a Class II laptop charger with a dummy ground pin, show me the label.

Battery chargers for say vacuum cleaners don't need noise filtering so they are Class II and only need 2 pins with no ground connection.

The Laptop is DC and thus not applicable and the case is DC grounded.

Perhaps the OP had tested a universal Class II Charger without a ground connection to the grid and that's why it was incompatible!

A proper Laptop charger with a Pi filter front end to ground looks like this on the red plug. Perhaps some before touch screens in UK were, but I have never seen one. Then you should be willing to do the RF leakage test I proposed.

Tony Stewart said:

Nigel Please read again.

The charger is Class II if double insulated from the grid connected bnut still needs to a primary CM filter to divert RF current to ground .

If you have a Class II laptop charger with a dummy ground pin, show me the label.

Battery chargers for say vacuum cleaners don't need noise filtering so they are Class II and only need 2 pins with no ground connection.

The Laptop is DC and thus not applicable and the case is DC grounded.

Click to expand...

Regardless it's still a class II device, and lot's of (certainly older) laptop PSU's only have a figure 8 mains socket for the power input (so no possibility of an earth), and still work fine - it's really just just a guess that it's anything to do with a missing ground.

If it doesn't work, then get one that does

Yes it is a guess based on physics. But I would wager all touchscreen laptops must use grounded chargers like every one shown so far HP, Panasonic etc and ones you claim to have tested without ground does not have susceptibility issue since they have no touchscreen and may not need a ground filter. With the touchpad, and audio ports, most do need SMPS CM noise filtering and some may not be enough.

I once had a ungrounded 12V supply for an android powered CNC gantry that would always fail on USB connected to a grounded tower or with a grounded laptop charger connected with USB on the ungrounded Android UNO with its unground PSU. I understood this right away and fixed it by either grounding the laptop, or the gantry or removing the grounded charger which was easiest to do, then the USB errors were eliminated. But grounded tower USB to UNO was error free as the CM noise is diverted to PE ground in the tower.

This proves the AC isolation Class I or II is irrelevant, but the ground is needed in the chrger to reduce CM noise to a lower impedance PE ground. This is also significant when DC ground is hardwired to AC ground OR when DC gnd is sufficiently isolated < ?pF ~ 1MHz compared with the surface area of the laptop to air nF to suppress the CM noise.

That is the purpose of my comments, to teach why things fail with physics ( and hand waving arguments (lol), not just toss it in the garbage.

That was 6 yrs ago for a $5k 1.1meter XY gantry that I designed for U of T to perform WPT antenna power grid measurements for wireless EV chargers to trucks.