Hacking the Dell laptop power adapter — part II

Knowing that the power adapter may have a DS2502-like chip, I started looking around for the OneWire protocol. There are actually plenty of documents and even source code for this protocol, and I happen to have some DS18B20 for verification purpose, I quickly came up with some code running on MSP430G2553 uC talking in this protocol. And I verified it’s working great with the DS18B20 device: I can read the unique device ID, and even get the room temperature.  After that, I wanted to try it with a power adapter. I choose a broken one I got from PC recycle pile. This one has broken laptop side connector, which is exactly what I need to connect the signal pin. So, 5 minutes wiring up, double check, and I ran my code. Guess what? Nothing!

I can’t even get it pass through the reset sequence, which is detected by device pulling down the signal wire, but I didn’t see that at all! I re-checked the wiring, and my code, verified it again with DS18B20, and found nothing wrong on my side.

After spending more than ten minutes checking everything, I decided to open the power brick to see what’s inside. After hurting one of my fingers I finally got it opened. And here is what I saw:

Image

This is the PCB side. The signal pin connects to a resistor (the black thing on top-left), and then go to the central pin of a TO-92 packaged component. The right pin is not connected, and left pin is grounded. There is also a diode-like device between ground and central pin, which looks like a reverse-voltage protection mechanism.

My multi-meter shows that the resistor is larger than 20Mohm, and zero ohm between any two of the three pins of the chip. All these results make me believe that this chip has been damaged. And it may be a problem of DELL’s design, since this signal wire has no shielding and the long wire can easily trap static electricity and damage the chip.

Here is a close look at the chip itself, and the reverse side of the PCB board

CaptureCapture

There are some text “01MFKVE BYTE TI” on the chip but I couldn’t find anything useful by searching it on internet.

Anyway, it’s not a waste of time, and I got this:

WP_20140207_005

By soldering the connector from power adapter side and a socket from a broken dell laptop, I exposed the signal wires from both sides and also the ground line. This will allow me to listen on the communication between laptop and a working power adapter, which is the next thing I’m gonna do.

To be continued…

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2 Responses to Hacking the Dell laptop power adapter — part II

  1. Pingback: Hacking Dell Laptop Charger Identification

  2. Kevin White says:

    Actually I think the biggest problem with their design is that the DC connector is arranged so that the centre pin is the ID signal, the inner surface of the coax connector is the positive output of the supply and the outer surface is ground. If you try to measure the output voltage with a meter it is difficult to avoid shorting the pin to the inner surface of the connector – that puts the 19V of the PSU onto the One-Wire data line. That destroys the device (well that’s how I did it!).

    Dell should have at least put protection on the device to survive that, there is not even any ESD protection on the PSU or the computer end!!!!

    kevin

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