Thinkpads Forum

My T400 just zapped me badly. Was sitting there and suddenly, whumph through the palm rest. Nearly knocked me off my chair.

(Note: I'm an ex-EE so am used to the odd shock but this is a little annoying).

This is NOT the first time this has happened. I had a T61 that did this to me a couple of times before but that was a faulty earth.

I'm in the UK so mains voltage is ~ 240v.

So I dragged out my multimeter and checked the voltage between the palm rest and ground (radiator). I'm getting 150v!!!! Well above the 30v AC lethal limit. No wonder I'm getting zapped.

Checked the earth in the house and I'm getting 0.3v between ground and earth pin in sockets universally. Well within acceptable range for leakage etc so this isn't an earth fault with the building.

So, all things point to the AC adapter. Checked the main power lead and it's fine.

Now this is supposed to be a "genuine" Lenovo 42T5275 (3 pin) but I didn't buy it directly from Lenovo but from a reseller. Picture here:

http://i.imgur.com/qsxM51I.jpg

Does this look like a dodgy one?

Annoyingly I only use a laptop because it takes less space so I'm eating the cost and dumping this now and getting an HP Z230 desktop instead.

Couple of other notes: has Lenovo moulded into reverse side, is a 3 pin adapter i.e. it has an earth pin, grey velcro, decent feeling connector.

ref: http://www.kawakami-ca.com/images/20v_dc_plug.jpg

You may have already done the following, but in case not, I would perform the following checks:

- with the suspect AC adapter plugged in but NOT connected to the laptop, measure AC voltage between outer shell of 20V plug (i.e., ground) to each of the three pins of the mains socket (hot/line, neutral, ground/earth). If you get > 30VAC with any measurement, you might have a bad supply.
- double check the wiring of the mains outlet for proper connection (orientation) of hot/line, neutral, ground/earth; could use something like this:

http://www.amazon.co.uk/Mains-Socket-Te ... B001SIE5DQ
http://www.test-meter.co.uk/socket-testers/

- plug the AC adapter into another mains outlet, preferably in another house, and re-measure the AC voltage potential between the 20V ground and that mains socket. If you get the same excessive voltages as in your house, that would pretty much confirm that the supply is bad.
- source a different AC adapter and repeat the voltage measurements

Been through all that. Definitely the supply.

I will crack it open tonight and have a look.