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Author Topic: *%&$^& Dell Laptop Power Supply!  (Read 11455 times)
WX7G
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Posts: 6052




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« Reply #15 on: June 22, 2010, 11:42:04 AM »

I'm thinking, perhaps incorrectly, that two of the three wires are powered off of 20 VDC from the power supply. And in the power supply is a circuit that connects between two of the three wires. This circuit is powered from the 20 VDC.
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AA4HA
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Posts: 1434




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« Reply #16 on: June 22, 2010, 05:35:25 PM »

The "third wire" is actually a bidirectional digital line that sends a serial message to the laptop when it is queried by the laptop.

You could dissect a Dell supply, isolate the chip (it will be on a tiny circuit board) and cobble together a new (cleaner) supply, then just add that chip to the third wire so the laptop is fat, dumb and happy. It interrogates the supply, gets some sort of digital serial message and thinks things are just great.

You may also be able to reprogram the I2C memory chip (EEPROM) to fool the laptop into thinking the supply has a higher rating.

http://www.embeddedrelated.com/groups/piclist/show/365.php

Dell batteries also use I2C to send status information about battery charge, charge/ discharge cycles and other information to the laptop. There are a bunch of devices in a computer that use I2C as a means of providing profile data (hard drives, adapters, etc...).

http://www.sharewareconnection.com/smart-battery-workshop.htm

If you can tap into the I2C bus you can read "a bunch of things" from all sorts of devices in the machine. I am certain that companies like HP and others also use I2C.

Another place you will find that chip is on the bottom of an AT-S909 radio. there are two tiny holes in the base (if you were standing the radio upright). That is an I2C bus connection for the manufacturer to flash in the initial channel loads in manufacturing. On my "git to it" list I wanted to make an I2C interface (plenty of schematics on the web) and see if there was a way to toy with the firmware in the radio or load new channel sets.

http://mysite.verizon.net/vze20h45/radio/sangean/909memory.html


Tisha Hayes
« Last Edit: June 22, 2010, 05:44:17 PM by Tisha Hayes » Logged

Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
W1ES
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Posts: 18




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« Reply #17 on: June 22, 2010, 06:33:04 PM »

No, thanks, on the "customer service" - I've heard enough horror stories now to swear that off forever.  Besides, this is an old machine I bought on eBay.

It's too bad, as it works great (except for the DVDRW drive, which stops working after 10 minutes, then you have to let it cool down).

I have done some cruising on some Dell forums and have learned that the "proprietary circuit" in use utilises a Dallas chip, diode and resistor.  Another tech has shown a way to remove these components from the PS and insert them on the motherboard and disconnect the third lead.  Once this is done, you can use any bloody power supply you want!

This will be my last Dell machine, as they continue to use this proprietary carp - apparently primarily as a vehicle to sell more accessories.  That is their right; just as it is MY right to not buy them.

It frosts me no end that I'll have to waste a half a day or more of my time to defeat this insidious feature.  If the supply didn't have such carppy filtering, I wouldn't be visiting this either.  Consider yourselves warned.

Thanks to all for ideas.  I'll re-post once I perform the surgery (if I perform it).

73,

Steve, W1ES

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K3AN
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Posts: 787




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« Reply #18 on: June 23, 2010, 07:10:42 AM »

For those contemplating a laptop purchase, I have had a succession of four IBM Thinkpad laptops over the last 15 years or so. None of them, including the current T43, has ever emitted a detectable amount of RF. They're also impervious to interference from my 100 Watt HF station, even though I have audio and USB connections to the radio and other devices in the shack.
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W1ES
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Posts: 18




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« Reply #19 on: June 23, 2010, 07:32:40 AM »

@ K3AN, have you also used their docking stations?

I'm really cheesed off that I was so stupid as to purchase this without looking around first, though I've found very little on the topic of RFI from Dells or any others, for that matter.

Here's the post on how to move the Dallas chip from the power supply (AC adaptor) to inside the laptop.

http://en.community.dell.com/support-forums/laptop/f/3518/t/19250464.aspx?PageIndex=2

Once I have the time (I only have a half dozen things going on at once at the moment, with FD on top of it all this weekend!) I'll post more.

73,

Steve, W1ES
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KF7CG
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Posts: 836




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« Reply #20 on: June 23, 2010, 10:27:21 AM »

Don't blame it all on Dell! I have a new or nearly new Dell laptop and have no problems whatsoever from noise.

From the description of the noise reaction it sounds as if some component of the supply is acting as an RF noise generation diode. This would have nothing to do with it being a switching supply and more to do with a near failure of some part in the power supply. Certain diodes, when properly biased can become broadband white noise generators. An article on generating a noise source using the same appeared in an older ARRL Radio Handbook or maybe it was one of the even older ARRL Radio Amateur's Handbooks.

Have you tried a different Dell supply or one of the Targus brand universal replacements?

The problem you are experiencing could well be an individual unit problem rather than a design problem. Not saying that it isn't an expletive deleted nuisance, but it may not be a design or brand failure just a bad supply.


KF7CG
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AA4PB
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Posts: 12844




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« Reply #21 on: June 23, 2010, 10:47:01 AM »

I've got two HP laptops, a Dell laptop, and two Dell desktops, one of which sits right next to my radio, and have no RFI issues with any of them.

Is the noise getting into the radio via the antenna? How far away is the antenna? Does the feed line have any common mode issues that might be coupling the noise into the radio?
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N8AUC
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Posts: 79




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« Reply #22 on: June 23, 2010, 11:13:11 AM »

I use the same vintage Dell laptop for precisely the same reason. I've got a Dell Latitude D510.
It has all the legacy ports, and much to my delight, no annoying nipple in the middle of the
keyboard. Bought it through the Dell Outlet Store. Got a whale of a deal on it at the time, too.

I use mine in the shack all the time, and have never had (in 5+ yrs) an RFI problem with either
the computer or the power supply. Frankly, it sounds like you just got a bad power supply.
And you bought it on e-bay, huh? I wouldn't bad mouth Dell for this one. Mainly because you
didn't buy it from Dell. When you buy on ebay, you "pays ya money and takes ya chances".
Sometimes you win, and sometimes winning isn't really winning.

You can purchase a replacement power supply from Dell. You probably don't want to hear
that, but it's probably your best bet at this point.

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W1ES
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Posts: 18




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« Reply #23 on: June 23, 2010, 03:20:32 PM »

Actually, two different supplies, two different labels, same trash on 6 and somewhat on HF.  When plugging in the docking station the noise gets even worse.

What makes me "badmouth" Dell is that, having found the power supplies inadequate, I can't easily solve the problem (by substituting a nice, quiet linear supply) because of their proprietary design.  BTW, for those who suggested using a Targus supply: that dog won't hunt.  Obviously, you haven't actually TRIED to use a Targus supply - because, if you did, you'd be swearing a blue streak much as I am.  The D610 has the "sensing" circuitry and software/firmware.  It's essentially a Dallas chip that has to provide the "proper" handshake in order for the system to work properly.

How would you like it if you had to go to the car dealership (stealership) to do every oil change, battery replacement, part replacement, or your car wouldn't work? (sounds of crickets chirping heard...)  Yeah, I thought so.

My plan is to dissect one of my good power supplies, dismount the Dallas chip and diode, supply a 100 ohm resistor, and build a pack that will mount to whatever linear, quiet, power supply I decide to use and provide the "proper" signal to the computer.

BTW, this has NOTHING to do with buying something on FleaBay and everything to do with crappy engineering.

over and out,

Steve, W1ES/4
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WX7G
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Posts: 6052




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« Reply #24 on: June 23, 2010, 05:10:45 PM »

The noise symptoms you describe tell us it is not switching power supply noise. PS (Power Supply) noise will be strongest in the low HF bands and will show up at discrete frequencies separated by 400 kHz perhaps. It is not wideband except in the VLF range where AC-DC bridge rectifier noise dominates.

It sounds like the docking station is spewing out noise, possibly from the USB bus. Connecting the external PS provides another RF ground path and could increase noise coupling, making it appear to be originating from the PS. A quick test of this hypothesis is to operate the PC and docking station off battery power. Without plugging in and powering up the PS touch the PS AC plug GND pin to the AC power socket GND. If the noise increases this says that it is not this power supply but the connection of it to GND that is part of the RFI onion.

A test of this hypothesis is to unplug the power supply from the AC wall socket but connect the power supply AC GND terminal to the AC socket GND.
« Last Edit: June 24, 2010, 10:15:58 AM by DAVE CUTHBERT » Logged
W1ES
Member

Posts: 18




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« Reply #25 on: June 24, 2010, 09:07:46 AM »

Well, I've come to a solution for now that will work.

Apparently there are power supplies (ac adaptors) that are "aftermarket" but are compatible with the Dell system.  I tried a different supply and the noise on 6 is down to about S2, which still sux but is acceptable.  I am going to let the tiger go back to sleep and avoid poking it any further with the pointed stick Smiley

The worst supply was trashing 6 if it was within 4 feet or so of the rig.  Disconnecting the antenna made the noise go away.  Unplugging the bad supply didn't make the noise go away until the supply had internally discharged.

As strange as it sounds, there must be some sort of broadband noise in the bad one that's around 50 MHz.  Can't 'splain it but would like to know just for giggles, so I may get my scope out and look at the + and - lines, as well as that damned Dallas chip signal line.

I still maintain that a system that requires a "special" signal line for an ac adaptor for a laptop was a lousy decision and, judging from all the comments I've seen on the various blogs and usergroups, a cause of much ill will toward Dell.  Sort of like their own Pinto gas tank only much more widespread ;-)

So given that I've resolved the cause of my agita, it may be some time before I follow up with a hack that will defeat the now-hated "feature" that prevented me from implementing my original solution of using an old Lambda 20V supply (still my preferred method, as that has zero noise!).  I honestly have many other things on my plate right now and this was but another distraction that had become a time bandit.

73,

Steve, W1ES/4
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AA4PB
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Posts: 12844




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« Reply #26 on: June 24, 2010, 09:28:08 AM »

"I still maintain that a system that requires a "special" signal line for an ac adaptor for a laptop was a lousy decision"

That depends on what you get in exchange. If the Dell system provides better battery charging and usage then the customer probably benefits from their system. Most customers don't try to adapt other power supplies to their laptops anyway. It's all about trade-offs and how you want to make them.

It would be lousy if there were an accepted industry standard for that control and Dell decided to implement their own proprietary system just so you have to get power supplies from them.
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KF7CG
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Posts: 836




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« Reply #27 on: June 24, 2010, 10:13:45 AM »

There is a sort of industry standard from what I see by personal experience. The standard is "Dell." Both HP, Dell, and the independent accessories manufacturer, Targus use the same type setups for many laptop supplies.

I believe that this is part of the new "ENERGY STAR" requirements for computers, both laptops and desktops. It is part of the schema in which the power switch doesn't turn things off. The laptop gets reduced heat loading (a real design nightmare in laptops), improved battery discharge life, better battery life through charging voltage control, and can live with the limitted cycle life of some of the Lithium type batteries. Then add to this that you can reduce the weight of the laptop a fraction and only power the control chips when there is AC power available.

It is actually a good engineering design for all but RFI and that could be prevented. By the way, the energy star requirements are getting tighter all the time and the power companies not liking what switching type supplies can do to loading waveforms when they are in reduced power mode are mounting all campaigns to get everyone to unplug all their electronics when not in use. This can sure be a bummer when you have to wait for 5 to 15 minutes for your satellite receiver, your HD TV, your Blu-Ray player, and all your other household electronics to reload themselves because the kids have watch the adds and listened to the talks in school and are unplugging all the electronics.

KF7CG
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W1ES
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Posts: 18




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« Reply #28 on: June 24, 2010, 10:16:40 AM »

I'll agree on that first point: most owners are PEBCAK's and idiot-proofing mostly works with them. 

It's lousy that there's no way to disable it.  Not a lot to ask.  If you're going to make a "fail safe" system, you darn wall better make the failsafe more reliable than the thing it's trying to protect.  Judging by what I've seen, this is not the case here.

YMMV,

W1ES/4
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WA1RNE
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Posts: 825




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« Reply #29 on: July 01, 2010, 06:09:49 PM »

 
 I don't believe you mentioned this, but did you try adding any snap-on type ferrites on the output cable?

 Start with a good size mix 43 ferrite close to the supply that will allow 2 or 3 turns of the output cable to be wound through the core - or add more ferrites.


 ...WA1RNE
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