CE Pro January 2023 - 24

Networking+Home Control
HDMI CORNER by DPL Labs
Can Your System's
HDMI Cables Be 'Too Good'?
TO GET DPL Labs to help
troubleshoot HDMI field
issues, first, the problem
has to be reported and replicated
here in the lab; then
we run through a litany of
measurements on the entire
system which typically
brings up some anomalies.
We then can take these
anomalies and either bring
in a patch or build a patch
for each one until the problem
is corrected.
Case 88 was pretty
awesome, and I have to
thank the distributor that
requested some help. The
setup was as basic as it
gets - a 4K projector, AV
receiver, and three input
devices, one of which would
not function. The integrator
was on top of his game
swapping all the cables and
replacing the one source
device not working. Yet
even with all that, the same
input failed.
There was one thing very
intriguing about the troubleshooting
the installers
performed. They ran the
cable from the projector
directly to the suspected
source and found that it
performed normally. That
would tell anyone the problem
was in the AVR. All the
cables used were from one
manufacturer and all were
0.5 meters. In addition, all
these cable products were
24 | CE Pro January 2023
designed to handle 48G
although the system was
18G set up. Makes sense,
if it can work for 48G it
must be a walk in the park
for 18G, right? Since all the
cables were the same and
replaced several times it
was assumed the cables
were not the issue.
confirmed. It was just a
perfect system! With nothing
left to try, the cables
were replaced with another
manufacturer's cables... and
the entire system came to
life. How could this possibly
happen? We tested
the 0.5-meter cables and
they were fantastic in every
The failure was due to an
extremely well-built cable for
48G used in an 18G-only system.
Under 48G, the rules for cable
correction are different than 18G.
The customer was in
Hong Kong, which made
things a bit more difficult
but not impossible for DPL
to test. First, all the equipment
was replicated down
to the cable assemblies
themselves. Upon initial
startup, we found that the
integrator was absolutely
correct. It just did not want
to work. Naturally, we went
through our normal test
and measurement process
using every instrument
available and previous case
studies to diagnose the
problem. There was no
single component anywhere
near breaching any specification
limit.
All voltages were
measured and stressed.
All DDC instructions are
way. So after a few hours
of engineering time we
decided to put two of the
0.5 meters cables together
in series with a cheap coupler
and boom, the system
came on.
You would have to
assume that the 0.5-meter
cable had something wrong,
but it didn't. We ended
up building a high-speed
attenuator at the output of
that one cable. With that,
we could attenuate the
signal, and although rather
crude, we were able to add
enough signal loss to the
single 0.5-meter cable -
and it was back to life. We
then used our generator,
which by the way can put
out a ton of signal level,
into the input of the AVR
and the answer was right
there in front of us. When
delivering the same signal
amplitude as the source
and 0.5-meter cable, the
AVR became unstable and
could not handle the input.
Was it the AVR? Not
really. The reason for the
failure was due to an extremely
well-built cable for
48G used in an 18G-only
system. Under 48G, the
rules for cable correction
(equalization) are different
than 18G - the correction
is adaptive with several
levels of EQ available and
can be selected, but under
18G there is only one level
and it is on all the time.
So the AVR didn't have a
chance, its internal 18G
cable correction was taking
the robust output of the
source and low data rate
of 6Gbps (three needed to
make 18) and shooting it
north into enough saturation
the AVR was out of its
range limit.
In this case, the cable
was just too good; both
the dealer and manufacturer
were happy with the
results and adds yet a new
addition to DPL Labs test
matrix. Keep those letters
and phone calls coming.
JEFF BOCCACCIO,
president of DPL Labs, can
be reached at info@dpllabs.
cepro.com
http://www.cepro.com
CE Pro January 2023

Table of Contents for the Digital Edition of CE Pro January 2023
