330W power supply for M17x update

So everyone that has done the 330W power supply mod that I posted earlier has experienced the power supply shutting down at 240 watts of power draw. That is pretty counterproductive since the M17x ships with a 240W power supply. I did some reverse engineering and some load testing and figured out what the problem is.

I built a simple dynamic load from a few resistors, two op-amps, and an IGBT that I salvaged from an old motor drive. I attached the schematic at the bottom for anyone that wants to build a similar device. I didn’t have a small enough current sense shunt resistor to handle the current, so I used feedback from the gate-emitter voltage since it is roughly proportional to collector-emitter current after about 10 volts. I also used an MC34072 op-amp since it’s what I had laying around. It’s a bit crude but it works.
The dynamic load let me test the power supply and confirm that it was shutting down at 240W. It did, with the highest power I could get at the output being 19.6V @ 12.5A, roughly 245 watts. I also noticed quite a bit of buzzing.
It is pretty unlikely that Dell would make a power supply that badly, and it successfully powers the M18x so I took a closer look at the only thing that could have any effect on the power supply: the ID wire. When I figured out how to put the 240W 1-wire ID chip in place of the 330W ID chip, I found out that the M17x couldn’t drive the 1-wire bus. Something was loading it down farther down the line. Cutting the ID trace after the 1-wire PROM fixed the issue and allowed the M17x to drive the bus high and charge the PROM so it would work (the PROM is parasitically powered). The only thing that could have an effect was whatever was behind that trace.
I had to remove a bunch of the white thermal stuff and follow the trace, where I found it goes through a buffer and then a comparator. With the power supply powered up, I found the signal was pulled high to nearly the rail voltage. Grounding the trace that I cut drove the comparator output low. With this figured out, I tried a load test with the trace grounded. Since it was cut, the M17x could still interrogate the power supply and accept it, while the rest of the line could be held low.
Load testing the power supply with the signal grounded resulted in a maximum output of 19.5V @ 22.5A before shutting down. It was also nice and quiet. That’s roughly 440 watts. Pretty amazing for a little sealed brick, and 33% more output than rated.

Apparently the M18x interrogates the power supply, and when it sees it is a 330W supply pulls the ID line low to enable the higher power level. Since it is convention to leave a 1-wire bus high, any other computer is only going to get 240 watts. So ground the signal trace that you cut on the other side of the 1-wire PROM. Enjoy.

Here is the schematic for the dynamic load. Components are just examples, I was trying out CircuitLab and there wasn’t a huge choice of components. Any op-amp and IGBT or MOSFET should work, but you may have to adjust the resistor values.

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Wednesday, July 10th, 2013 Electronics

10 Comments to 330W power supply for M17x update

  • Rafael says:

    I’m using a modded 240W dell PSU in my clevo notebook (ID wire cutted and power cable changed). Could I do a similar approach in order to make a similar PSU work in my clevo?

  • khenglish says:

    awesome! thank you for looking into this!

    I assume when using this PSU on a clevo that we can just tie the ID line to GND since clevos don’t check ID? Don’t even need to desolder the cooling plates to do that so that’s why I ask.

  • sangemaru says:

    Awesome work mate. We were initially thinking that we’d try soldering the ID chip to the m17x-R2 mobo and just using one of those HP 350W PSU’s, but I’d love this much more. Great work and many thanks.

    Btw, we did manage to run crossfired 7970m’s on the 240W PSU, but it was pushing it :P Thanks to you, this should go a long way to more performance out of the R2.

  • sangemaru says:

    Oh, forgot to mention. Your workbench is looking awesome.

  • imsolidstate says:

    Right, if you don’t need to get the ID then just tie the whole signal to ground.

  • Sach says:

    How do I put that ID chip directly in the laptop? Please provide a detailed explanation.

    Thank you kindly

  • khenglish says:

    I soldered together the ID line and GND and it worked. PSU never shuts down now. Thanks for looking into this!

  • Sach says:

    @khenglish Could you provide a basic guide into how to solder the ID line and the GND. I removed the entire ID chip from one of my psus in the hope of exposing less of the cabling. I basically get power to the laptop, but it is not recognizing the psu ID at all. That’s the only thing I need to fix. Buying many new flextronics and delta adapters didn’t help. I’ve even replaced the DC jack on the board to no avail. Power received. No PSUID received. Gotta find out exactly how to solder the psu ID chip inside the laptop so ID is always read as “240w” in bios. Please help. You can send me an email if you like. sach4christ@gmail.com

  • King of Interns says:

    Would love to give my M15x more power. Currently the 7970M and 920xm do not get enough. Are you able to mod and sell a 240W or 330W unit to people with no electronics knowledge like me.

    Greatly appreciated! Look forward to your reply!

    Thanks

  • Fernando says:

    I have an asus g73jh. I ordered a dell 330w PSU. I was wondering if you had a guide?

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