Shady Dell laptop practices

On some of the inexpensive Dell laptops they implement a hardware-lockout system intended to prevent you from using aftermarket charger bricks to charge the battery. The way they do this is there's a chip in the Dell charger that contains a unique identifier which a chip on the laptop mobo requests from it on startup over a one-wire interface.

If on boot the BIOS can't confirm that the lockout chip on the mobo has asserted the "OEM OK" pin or whatever the BIOS then proceeds to muck around with the processor MSRs (model-specific registers) and alter their state, specifically the BD_PROCHOT register, which is a flag bit that is usually controlled by the motherboard temperature sensor.

Flipping that makes the processor think the motherboard is overheating, which disables battery charging and has the additional nice "feature" of throttling the processor down to around 400MHz from 2.8 GHz or whatever. So not only can you not charge the battery you can't really use the laptop on an aftermarket brick even when plugged into the wall. Also there's then no way to tell if the laptop mobo is _actually_ overheating in that state.

Good news is that the MSRs are accessible via software, so it's not hard to write a script that runs after the OS start to flip the bit back, and everything is back to normal.

Reply to
bitrex
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My Dell laptop charger used a Dallas-Maxim DS2401 serial number 1-wire device. I didn't know if Dell bought a block of pre-assigned ID numbers of whether any 1-wire ID would work.

When the Dell charger died I transplanted the TO-92 sized (easy to handle) DS2401 from out the original into a kludged splice in the cable of the replacement charger - which claims to have enough current capacity. The laptop is happy.

piglet

Reply to
piglet

They're trying to avoid the bad publicity of a laptop spontaneously combusting because some jerk charged it with a knockoff charger.

Reply to
bloggs.fredbloggs.fred

It's superfluous from a battery-charging safety perspective; the laptop's charge management system/IC is perfectly capable of handling an under-spec aftermarket charger being plugged in. It'll have undervoltage lock-out and likely can sense the brick's output impedance well enough to crowbar the charging current to a safe value if the input rail starts sagging. It won't be the laptop itself that catches fire, in any case.

If it's really an important safety/PR-protection device it raises the question of why it's implemented on some models and not on others.

Reply to
bitrex

got a link to such a script?

Reply to
mike

This isn't a shell script but can be saved as a .c file and compiled with gcc so it's in theory OS-independent (though I believe "asprintf" may be Linux-only so that line might have to be changed). Requires superuser/root/administrator privileges to execute successfully

formatting link

On the Window's side there's also a tool called "ThrottleStop" which has a radio button that can be clicked to toggle the bit manually.

Reply to
bitrex

I woundn't own a Dell if it was free. They are the worst brand sold. They use parts made only for their systems. Even their case fans are made just for Dell, and they cost a fortune. I have my preferred brands, even though I build my own desktop machines, but Dell is not even on my list. I'll leave them in the store so someone else can waste their money on them and then dispose of them.

Dell is Garbage !!!

Reply to
oldschool

They were pretty solid in the 1990s, but I think there's a good reason they're not publicly-traded anymore.

Reply to
bitrex

They may be doing some other stuff, you don't know.

Reply to
bloggs.fredbloggs.fred

I love Dells! I have found the commercial-grade models to be VERY good. I have had several Dell destop (Optiplex) machines run over 12 years in 24/7 operation. Yes, a lot of stuff in them is special, for instance the fans are made to be extra low-noise. Who cares, as you can put new bearings in them if they get noisy, or buy replacements on eBay.

I have also had really good luck with their laptops, but again, there are some really great models and some that are a bit mediocre. I buy all my Dell boxes used for, usually, under $100 delivered.

I did just have a motherboard go bad. First, it was bad capacitors, but then it just got sick. Possibly it is a bad capacitor with no visible signs. I only replaced the obvious ones.

Jon

Reply to
Jon Elson

Excellent and interesting info on the flag.

I knew there was something that told the laptop to charge or not quite a while ago. I wasn't sure if there was a "signal" in that 3rd line into the charging jack OR just a simple voltage that the motherboard reads. I looked into the broken charger and did not right away see anything that obviously send a signal or squarewave or anything.

Next, I tried a cut charging cable to monitor the line but of course, the charger I used was broken anyway so no luck there. I have so many extra chargers now, I just haven't cared that much to dig into it again.

boB

Reply to
boB

What about overvoltage and reverse?

The input circuits I've seen, it's more or less straight into the MOSFETs. Maybe a ferrite bead, but that doesn't do jack, it saturates quickly during input transient (and maybe the ceramic caps too, if allowed to overshoot) and in operation. No TVS.

It's a very real possibility. I had one mobo get nuked because of a frayed power supply. What happened is the coaxial cable (they're constructed with two braid layers, carrying current, with a data line in the center) got frayed at the PSU's strain relief, and was shorting out intermittently. Somehow or another, this caused enough stress to blow up a couple parts (presumably there was a general power surge that took out whichever chips broke down soonest).

The bizarre thing is, the most burnt chip was an LM393 near the battery controller. How, and why, and also why?...

Possibly, if there had been a TVS diode on the input, that wouldn't have happened.

Tim

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Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Contract Design 
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Reply to
Tim Williams

Den tirsdag den 9. januar 2018 kl. 02.05.25 UTC+1 skrev Tim Williams:

don't think it was ~20V into the data line that killed it?

Reply to
Lasse Langwadt Christensen

Shifting the cost of a fault-tolerant power input/charging circuit onto a vendor-locked-in consumable item on the low-end models also seems a reasonable possibility, yeah. Who _would_ want to spend money on extra circuitry to protect their product from someone else's bodge-job?

But that it's a "safety feature" seems disingenuous; other major manufacturers are apparently confident enough in their designs to not be so concerned about aftermarket chargers being used. "Safety" from their own corner-cutting, more like.

Reply to
bitrex

I blew up a GPS antenna the same way. If there is an intermittent short at the end of the cable, when the short is on, current flows through the cable which at DC appears as a good size inductor.

When the short opens, the current wants to keep flowing so the voltage raises to whatever it takes to keep the current flowing.

m
Reply to
makolber

All brands go bad eventually, but I have not been impressed at all by Dell. My preference is Lenovo. I am posting this from an 18 year old Lenovo computer running Win98. I did have to replace the original power supply (which was under rated), but thats probably because I added a bunch of drives and stuff. Otherwise it's still the original motherboard which has never needed any repair aside from changing the CMOS battery. I run this system to the limit too, as far as RAM and drives.

When I changed the power supply, I went from 100W to 350W. More than enough...

Reply to
oldschool

The commercial Dells might be a lot better. I never saw one of them...

Reply to
oldschool

If it's an 18 years old Thinkpad, it's an IBM and not a Lenovo!

I did have to replace the original power

I have probably 20 Lenovos of various vintages stashed away--T42s for DOSish things and T410-T430 for daily use.

Cheers

Phil Hobbs

(Posting this from a 24-core AMD server that doesn't have a management engine and doesn't suffer from the recently-disclosed hardware bugs.) :)

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Dr Philip C D Hobbs 
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Reply to
Phil Hobbs

Some of the old IBM Thinkpads were pretty nice. Some less so. Too ancient for much use now though.

NT

Reply to
tabbypurr

Someplace I still have a couple of Butterflies, the ones with the folding keyboard. It was designed by a friend of mine, the late great John Karidis.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
Principal Consultant 
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Reply to
Phil Hobbs

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