Re: Laptop video noise -- help

G-squared wrote:
On Jan 26, 3:12 pm, pj <pj4...@xxxxxxxxx> wrote:
> Need a means to filter the power going into an
> HP zv6000 laptop. Got it hooked up (S-Video) to
> our HDTV to display Netflix streams off the
> Internet.
>
> Does an OK job when on battery.
>
> On a.c. power (from the HP, made in China,
> 'brick') there's video noise on the screen.
> Visual appearance looks like faint 60 or 120Hz
> noise. (two wide bands) Within the low-freq
> bands, there are faint herringbone-like
> patterns, probably some harmonic of 60Hz and
> many small pulses like ignition noise.
>
> This 120watt 'brick' puts out 18.5vdc @ 6.5amps.
> So, i'm hesitant to try any off-the-shelf 12v
> automotive filter.
>
> Choices are building a heavy duty power supply
> that would be clean (and probably not as
> efficient as the brick), designing/building a
> filter for the brick or, buying an in-line
> filter (preferable.)
>
> Have tried googling for a 24v filter (on boat
> and RV electronics sites) but haven't seen anything.
>
> Any tips, suggestions etc. ???
>
> TIA --pj

OK, the 'electrical police' will want to cart me off for this
suggestion. If the laptop power supply uses a 3 wire plug, try lifting
the ground with one of those '3 to 2' adaptors. If it's only a 2 wire
you could try reversing the plug though that is less likely to have an
effect.

Linear power supplies are typically quieter than switchers BUT they
are much less efficient (run hotter) and much larger for a given power
level.

A 'pi network' with a few large electolytic capacitors AND some mylar
or ceramics with large value inductor (coil) could knock down the
herrigbone but is not likely to deal with the 60 Hz noise. Also, the
power supply may not start properly with the filter as the in-rush
current may trigger an over-current fault in the supply.

Or get a REAL BIG battery

GG

Thanks for all the good 'thought nuggets.' Particularly, the reminder about the starting & protection frailties of switching supplies.

Yup, the 'brick' is a three pronger. Did the 2-3 adapter game with no supporting ground. Slight difference-- herringbone rode up higher in the 60hz bands. Impulse speckles remained in about the same area of each band.

Could be a general circulating ground issue. There there are grounds all over the place: OTA, LAN router, Cable-TV, DVD player, HT, some capacitive coupling back through the power brick, HDTV at the wall plug. JVC used two prongs on that so who knows how they are bringing their chassis to 'earth.' -probably via another capacitor since this mess isn't tripping the GFI.

Checked and found the LAN router & cablemodem are on another a.c. circuit --on the opposite side of the 120/240 line from the HDTV, notebook etc. Pulled the CAT-5 connection to the notebook and put it on wireless -- still had the noise.

Although this may be a 'mulligan stew' of circulating grounds, I tend to blame either the power 'brick' or the way HP is powering their their S-Video interface.

Perhaps found a work-around. Checked to see if the S-Video connector shell was solidly connected on both ends and noted a D-15 RGB input socket on the back of the TV that I hadn't paid any attention. No clue as to how the RGB bandwidth will compare with S-Video but will stop by Fry's tomorrow, buy a cable and give it a try. Might be the way to go -- this notebook has done an OK job when hooked to a conference room projector and Smartboard. That screen has about 2-3 times the area as this RPTV.

(However, the conference room at work has a video amplifier between the notebook pigtail and the projector so don't know what kind of conditioning or filtering that might be doing.)

Thanks again for pushing the 'engage' button on my brain.

Now, the pi filter will be a last resort.

--
pj

.

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