Measure voltage output of My Lenovo charger.. how? (failing charger?)

[cfixer]

Hi
I'm sitting with this type of charger because i want to diagnose if it's failing,
for a T410s and wondering why i get zero volts if i try to measure voltage output, am i doing it wrong?
https://www.ebay.com.au/itm/20V-4-5A-Ac ... 3078194329

I use a Multimeter and do the following
1) I connect a red plug to the inside of the yellow charger head (the pin inside the charger)
and connect the black ground to the metal outside of the charge. But i always get zero voltage, if i set it in measure corrent mode
I get a spark. If i connect Charger to Motherboard i do get voltage readings from the motherboard. So how do i correctly measure the voltage output of a Lenovo Charger?

Please help,
Kind regards
Cfixer

[cadillacmike68]

Try putting the hot (red) lead on the inner barrel of the plug. I got 19.75 volts on one of mine doing this. I think that center pin is a special signaling pin for the adapter's power or something. Look at some W530 threads on the 175W adapters for more info.

[cfixer]

That Helped, thank you

It's strange: Sometimes i get 20.3 and sometimes 20.2 it jumps up and down.
Is it a bad sign when i do measurements of motherboard or charger if the decimal values change by one value or jump like that?

[atagunov]

Sometimes i get 20.3[/b] and sometimes 20.2 it jumps up and down

The miniscule variance in measured voltage doesn't bother me at all. Think that's okay.

I'd still prefer an original charger any day of the week to a knock off, just because. Think original should be pretty cheap for both 65Wt and 90Wt. The one you have btw proclaims itself to be a 90Wt (20*4.5 = 90).

And given that you already have one Thinkpad that has mysteriously failed and that the failure could well be related to power supply circuits.. I'd definitely consider switching to Lenovo-branded chargers. Any Lenovo charger with a round-barrel output will work for you. Okay maybe 90Wt is preferred to 65Wt especially for home use. Doesn't hurt to have a little more omph. And maybe a 65Wt for walking about town since it's smaller/lighter

[cfixer]

I decided to measure the Volt on the DC in Pins on the motherboard, and look: One of them is only 1.5 and sometimes 7.5, Not 20.2.
https://ibb.co/0M0tnPy

Do you think this might be the problem? I would think all 3 pins have to output 20 Volt right? (yes I really want to learn this )


tagunov: Good point on having an actual charger from the original company, there are so many chargers it's easy to get confused at times

[atagunov]

Hi, I'm under impression that one of the contacts measuring differently is not an indication of an issue.

The plug has 3 contacts: inner and outer round metal bands and the pin in the centre. The role of the pin in the centre is quite special. Somewhere inside the plug sitting on the end of the wire coming form the PSU there may be a hidden resistor. The nominal of this resistor tells Thinkpad what kind of charger it is: is it a 65Wt charger? A 90Wt? A 135Wt? This tells Thinkpad how much Wt it is okay to pull from the charger. And Thinkpad measures that resistor. To measure that resistor Thinkpad arranges for some current to flow through it. The voltages you're seeing: 1.5V, 7.5V are probably the result of this measuring activity.

[bgravato]

About the center "signal" pin:

http://thinkwiki.org/wiki/Power_Connect ... _connector

[kfzhu1229]

Actually even if you measure the power pin to ground, just seeing there's 20V there is not good enough.
Especially when you have low wattage or cheap chargers, seeing the voltage drop when a load is connected is more important.
If you can, find a capacitor or MOSFET or something on your motherboard that's connected to the 20V almost directly and see the voltage when the machine is switched on just sitting in BIOS.
If that's anything below like 17V, you have a failing charger.