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7.9mm Round Jack (old type) to Square Plug End (new type) Adapter Pigtail

Posted: Fri Apr 05, 2019 9:06 pm
by Renz
Hi there

I can't get my W520 power supply to charge my P50.

https://photos.app.goo.gl/nTGexDG2fE5WQQuSA

Anybody has an idea let me know.

A bit of a head scratcher that one

Re: 7.9mm Round Jack (old type) to Square Plug End (new type) Adapter Pigtail

Posted: Sat Apr 06, 2019 12:36 am
by w0qj
Do you have another ThinkPad Slim Power Conversion Cable you can try? Perhaps the one you are using is broken?
ie: It looks brand new to me: your 79mm Round Jack (old type) to Square/Slim Plug End (new type).

The reason why we suggest this is,
~We bought a pack of six (6) unofficial Slim Power Conversion Cable.
~Upon arrival and testing, only 5 of the 6 Slim Power Conversion Cable worked! One was broken!

Re: 7.9mm Round Jack (old type) to Square Plug End (new type) Adapter Pigtail

Posted: Sat Apr 06, 2019 5:53 am
by RealBlackStuff
Probably a missing/wrong resistor inside the adapter's square plug, between sensor-pin and ground.
Your 130W charger probably is recognized only as a 90W, not enough to charge a full-blown W520 with quad-CPU, discrete GPU and loadz of RAM.

Re: 7.9mm Round Jack (old type) to Square Plug End (new type) Adapter Pigtail

Posted: Sat Apr 06, 2019 11:33 pm
by Renz
Yes it does exactly the same thing as a 90w

How could there be the wrong resistor in there? Why would there be a resistor at all in the first place??

Re: 7.9mm Round Jack (old type) to Square Plug End (new type) Adapter Pigtail

Posted: Sun Apr 07, 2019 12:33 am
by axur-delmeria
Renz wrote:
Sat Apr 06, 2019 11:33 pm
How could there be the wrong resistor in there? Why would there be a resistor at all in the first place??
The laptop measures the resistor inside the connector. Different wattage chargers have different resistors.

In the old type (round plug), 9.5-10k ohms means 65w, and 0 ohmsdisconnected means 90w (can't remember the values for 135w and 170w) . IIRC they changed it in the rectangular plugs, but I'm not familiar with the new resistance values.

Correction: for 90w charger no resistor is connected. More information (including the new rectangular plugs) here: https://www.thinkwiki.org/wiki/Power_Connector

Re: 7.9mm Round Jack (old type) to Square Plug End (new type) Adapter Pigtail

Posted: Sun Apr 07, 2019 5:04 am
by RealBlackStuff
Before you do anything, measure the resistance between middle-pin and ground on your (unplugged!) 130W adapter with round barrel plug.
Do the same with the (unplugged) rectangular adapter-plug.
Let us know what you find.

Cut/slice the rectangular plug along both narrow sides, then fold it open.
You may (not) see/find a resistor between middle sensor-pin and ground.
Replace the current/missing resistor with a 1 kΩ one to 'trigger' 130/135W.

But as far as I'm concerned, it should be enough to just remove any resistor (if present) and then direct-connect the sensor-pin to ground.
After all, the round barrel from the original charger should already have the required resistor, so the adapter, which is just a feed-through, should not need yet another one.

Someone did a similar, but more complicated, job here: http://marc.merlins.org/perso/linux/pos ... -P70_.html