CE Pro December 2021 - 22

Networking+Home Control
HDMI CORNER by DPL Labs
When You Thought You Saw
Just About Everything ...
SOMETHING NEW ALWAYS
comes up, you can bank on
it. Unlike so many HDMI interoperability
issues that are
somewhat easy to identify,
this instance was not - and
nobody knew until DPL got
its hands on it. Here's what
happened.
As with many cable providers,
products are sent into
DPL Labs for testing. They
can follow a few options. If
the provider is a member of
DPL, they get to send their
cable products in for a pretest
so they don't get stung
paying all that money to the
emissions people for approval
in case their cable didn't
have an extremely good
chance of making it. Then
there are non-members,
who send their products to
our sister company InVisions
Technology for testing and
pay a fee. OK, that said, let's
dig into the meat.
This cable provider is a
DPL participant and was able
to have the cables pre-tested.
We put these samples up
in the queue and ran the first
set of 12G eye patterns. The
eye was formed but it looked
a bit odd, as if someone took
a hammer and smacked it
right in the middle of the
waveform. The product still
achieved minimums, but
with this kind of shape it was
destined to be problematic
in the field.
Digging a bit deeper, we
ran frequency domain tests
with a variety of S Parameters
and extra DPL stress analysis
functions. There it was - a
28dB suck-out at 11G (see
Fig. 1). Now what you have to
remember is that most of the
energy in this transmission is
down toward Nyquist, about
6G, but this caused response
issues that were just too
dangerous. Turns out almost
all the samples we received
were the same way. But why?
This was a doozy. Where
do you even start? As usual,
by ripping up the cable and
inspecting the wire layout and
its sub-assemblies along with
the connector itself. These
cables were soldered with
automation, so you would
have thought all was good. It
turned out the ground shield
over the connector assembly
had an itty-bitty pin hole at
one end that was common
among most of the sample
cables. Trust me, I did not
find this; credit goes to one
of our super " Black Magic " RF
engineers who managed to
detect it.
The pin hole created a
mechanical L/C filter shunt
at 11G, reducing the output
by 28dB. We re-soldered
the shell with some heavy
amounts of silver solder
flowing over the copper foil,
drowning the shield in solder.
Fig. 2 shows what happened
to the signal response after
the reflow of solder - a
huge improvement in response
and performance.
Needless to say, we informed
the DPL member and
provided a detailed report as
to what was discovered and
the procedure on how to correct
the problem. The cables
were never sent for emissions.
A change in production
procedures would have to be
made, not only in the process
but with the automation system
building the devices. We
shall see effectiveness when
the cables come back.
This just demonstrates the
complexity of these products
when you start running
data rates as high as 12G per
channel. The higher the data
rate gets, the more vulnerable
the interface becomes.
Details in the manufacturing
process must be kicked up
a notch today. One minor
slip-up can introduce field
interoperability problems all
over the world.
Fig. 1
Fig. 2
DPL Labs assisted one manufacturer when it discovered a pin hole had curtailed performance
common to a sample cable set (Fig. 1) and re-soldering produced a big improvement (Fig. 2).
22 | CE Pro December 2021
JEFF BOCCACCIO,
president of DPL Labs, can
be reached at info@dpllabs.
com, or visit dpllabs.com.
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CE Pro December 2021

Table of Contents for the Digital Edition of CE Pro December 2021