[SCCC] Incredibly Noisy Power Supply

[Ken Alker]

I believe that third conductor is called a "smart pin".  Try Google and 
search on "HP power supply third pin" or "HP smart pin".  There are more 
articles than you can shake a stick at, many unuseful, but I'm sure after 
an hour of reading, you can find your answer (or ANY answer you want, for 
that matter ;-).  The most useful I found after 10 minutes was this one: 
https://www.techspot.com/community/topics/smart-pin-voltage-to-capacity-correlation-for-laptop-power-supplies.178875/. 
As always, read 100 of them and see which answer floats to the top. 
Hopefully someone else on this list who has actual experience with this 
will submit the exact answer, but I think this link gets you pretty close.

I own Santa Barbara Electronics Supply.  We are the old MarVac/DOW in this 
area (similar to Radio Shack of the 70's).  I sell dozens of DC barrel 
connectors (most sourced from LKG/Philmore), and (as I recall - I'm not at 
the store yet this morning), one is called an "HP connector".  I usually 
stock these and I sell one from time to time.  I never knew why the 
manufacturer calls it an "HP connector", but now I bet I know why.  If you 
need one, let me know and I can mail it to you, or you can come up and 
visit beautiful Santa Barbara and make a weekend out of it (except we are 
closed weekends now due to lack of employees due to COVID-19).

Good luck.

Ken Alker
KA6KEN
805/681-2524 (store)


--On Friday, April 23, 2021 12:55 AM -0700 Steve <k0xp at k0xp.com> wrote:

> Pour yourself a cuppa and sit back, as this is kinda long...
>
> I could ask about this on some computer forums; but those guys likely
> wouldn't have the vaguest idea what kind of noise I'm talking about, nor
> why I'm bothered by it. I'd likely get all kinds of suggestions and
> questions about my software, operating system, amount of RAM, and
> what-not, none of which figures here anyhow.
>
> I have a fairly-new HP laptop (that my brother gave me) that uses a
> ubiquitous 19.5V 2.31 amp switching supply. When this switcher is plugged
> in and charging, the radiated noise level is so high that my S-meter
> reads S5 on 80 or 40 and S7 on 20. I haven't tried 160 or 15 but I'm not
> nearly as concerned about those bands, as the bands I'm most likely to
> use at any given time are 80, 40 or 20.
>
> The laptop connector isn't simply a two-pin coaxial type; it apparently
> has a battery sense connection inside the shell surrounding the center
> pin. I built myself a nice little regulated 19.5 volt linear power supply
> and after testing and being satisfied it wouldn't go apes and kill my new
> laptop, finally got around to cutting the DC power cord between the
> switching power supply and laptop so I could splice in connectors to plug
> it into the new linear supply, only to discover there are THREE wires in
> there, not just two. That's when I carefully examined the insides of the
> connector and noticed the inner coaxial shell surrounding the center pin.
> After temporarily splicing the cable back together, I measured the
> voltage on the third blue wire (the two main DC wires are conveniently
> red and black), I found the blue wire to snap up to 19.5V and sometimes
> down to 0, but also sometimes some value in between, apparently depending
> upon what I was doing with the laptop and how much current it was drawing
> from the switcher.
>
> Looking on epay, I find these power supplies available for a few bucks
> and extremely common. My brother's newer Dell laptop has the same power
> connector and voltage/current ratings on his switching power supply
> (which looks identical to mine except with different markings; it even
> has the same design strain relief on the DC cord). The connector seems to
> be 4.5 mm OD, 2.5 mm ID, according to the epay vendors. It's similar to,
> but not like, the power connector on my old Sony Vaio laptop, which DID
> have only the two power wires in its cable (and whose center pin is much
> thicker, as well as not having that center shell connection).
>
> Of course, I've tried ferrite beads on both the AC input and DC output
> supply cables, to no avail. Thus, I conclude the switcher is likely
> radiating all by its lonesome (the laptop is almost dead-quiet in the
> radio(s) when not plugged in, with just a little bit of scratching noise
> when I scroll the screen).
>
> Other than mounting that dang switcher inside a metal box then filtering
> the heck outta all wires, I can't think of what else to do right now. I'd
> love to use my custom-built linear supply but am now reluctant to plug it
> into the laptop, in case the laptop NEEDS some sort of signal on that
> third blue wire and otherwise goes apes or dies, itself. The switcher's
> plastic case is solidly glued together. I suppose I could buy an
> epay-special then break apart the plastic case to try to see whether that
> blue wire's connections might be easy to emulate; I guess that's my next
> step. I have little hope of being able to reverse-unjinere that switcher,
> however.
>
> Would anybody happen to know what that third blue wire actually does,
> what signal it carries, and how to emulate it on a homebrew linear
> supply? Or maybe even know of an available linear replacement power
> supply?? Surely, I'm not the only character who's come across a filthy
> switcher for these newer laptops.
>
> Thanks,
> SteveH K0XP
>
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