The HDM-DAD was developed by Jeff Boccaccio with the professional installer in mind, it’s purpose is to verify that all of the EDID signals aka Low Speed Data feeds have the necessary integrity.

The HDM-DAD provides analysis of the Low Speed Data Stream which includes the 5 volt feed from the source to the display, the Hot Plug Detect return voltage from the display to the source, the Data line and the Clock feed. The LED display lights on the top of the case indicate the status of these EDID components. If there are issues with any of these feeds the DAD will repair them.

The HDM-DAD every tool box should have one.

OK. House keeping duties done, let me show how to use the HDM-DAD and how to make your life better.

In the HDMI world there are two types of Data; High Speed which is your audio and video feeds and Low Speed lines. The Low Speed lines carries the questions (your source) and answers (the display) that must be negotiated prior to the picture and sound starting.

These questions include:

  • What are you?
  • What is your firmware?
  • What resolution do you want?
  • Do you want audio?
  • If so, what kind?

And most importantly….

  • Is the line between us secure with HDCP?

Again it is problems with the Low Speed or DDC lines that cause the vast majority problems that the CI will see in the field.

First lets discuss what the typical EDID issues are and how the DAD fix’s them.

The most common malady that HDMI systems suffer is capacitive loading of the DDC lines aka low speed data. This capacitive loading results in the slowing of rise times as the data transfers from one state to another. This capacitive loading may come from just about anywhere, bad circuit board design or build, bad cable design or build or it could just be because its tuesday. This issue results in the slowing of rise times as the data transfers from one state to another. These states are for convenience symbolized by “1’s” and “0’s” with a “1” being 5V and the “0” being no voltage (EDID is just a relay like a light switch 5V on and o volts off) [have a light switch for demo]. When the rise times of this data is increased the ability for the voltage to be in the correct state (either 1 or 0) when the clock ticks is diminished. [see pic. #1]. When the clock is missed the data sentence becomes garbled and not understandable. This problem will manifest itself in several ways.

The first and most common is the dropping of the audio, you may also see long delays when switching between sources or channels the final EDID straw will be the failure of the HDCP handshake.

When this handshake fails picture and sound are all gone (bye bye). In the past you would unplug the HDMI cable wait a couple of minutes, plug the cable back in and Viola it works….for a while and then you are back in the same place. The DAD solves all of this by stripping the capacitance off of the DDC lines, which will return the rise time to 270 Nano Seconds. This will take the choke hold off of the data.

Next up is the placement and direction of the DAD.

In the beginning we planned for the DAD to be placed at the display side with the input connected to the source and the out to the display, at that time the vast majority of problems were in fact caused by the source so the real work was done at the display or sink side.

However times have changed and with overall drop in the economy the sources are becoming the  primary culprit. What this means is that now you will start by placing the DAD at the output of the source that is having the issues (example; Blu-Ray player) with the signal flow pointed toward to display. If all sources have the problem place the DAD at the output of the AVR, in this application it is generally best to reverse the direction of the signal flow.

And lastly, understanding the LED diagnostics display.

There are four LED lights on the DAD and they can tell you a whole lot about where is “Not” working.

The DAD looks and displays the status of the following signal lines.

5 Volt; The 5 volt line is the voltage only trigger that that request’s the display to wake up.

Hot Plug Detect; The Hot Plug Detect is the voltage only feedback from the Display to the Source that tells the Source that the display is there and ready to accept data input.

Clock; The clock line is one of the most important data lines, without the Clock feed the display would have no idea where and when the data should be placed.

Data; The Data feed carries all of the questions, answers and HDCP signals. This is the data that sets resolution, audio format, color depth etc.

Reading the lights. The LED’s really do tell you a lot.

Here are some of the things that you need to see when the source and display are connected and just turned on.

HP LED needs to be lit, 5V needs to be lit and Clock and Data will be flashing like crazy, once the picture and sound are on the display the clock and data feeds will usually flash in sequence about every 1.5 – 3 seconds. If they are flashing faster or in an irregular pattern that is telling you that the DAD has work to do and is doing it.


  • “5V” not lit.

Make sure that the source/AVR is turned on. Replace HDMI Cable(s). Connect the DAD directly to the source.

  • “HP” not lit.

Is 5V lit? If not check source status. Make sure that the display is turned on and in the correct input. Connect the DAD directly to the display.

  • Clock/Data not lit.

If you have a DirecTV receiver (and some CATV STB’s) do not worry, this is normal. Check to see if all sources/display are turned on and in the correct input. Replace HDMI Cable(s).


Brent McCall
Ethereal Home Theater
Product Development and Technical Support
(386) 846-7264