DPL Labs has been working with many major AVR and display companies helping them work out AOC (active optical cable) functionality issues since late summer 2023. During that period, approximately 14 additional issues were identified. These AOC/AVR issues range from power supply management to input/output ratio levels, and some high-speed properties that require tighter tolerances. Most recently, another failure was brought to our attention that involved a new 30-meter AOC that came stock with both source and display power supplies to guarantee its power and stability.
It falls under power management again, but this one was a real doozy. We received just one sample of this device, but it was at least a way to find out where the problem was. The integrator installed the device with its external power supplies and AVR and received no response.
The integrator then removed the power supplies and tried it again. There was no improvement. He finally replaced the device with another of the same make and model. Again, the unit did not respond.
The integrator finally replaced the AOC with a different make and model only to find out the AVR still gave no response. That’s when DPL got involved. We instructed the integrator to replace the AVR and AOC at the same time as an experiment to try and help resolve the power supply issue, which he did, and the system came to life.
So, what causes this to happen and how can it be prevented? We asked that the first AVR be sent to us along with the original AOC that did not work, giving us all the samples and tools we needed to diagnose the real issue: that being the power supply. It turned out that the AVR’s HDMI supply voltage was non-existent.
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Since the first try used the external supplies, the AVR was not affected, but when he used it again without the external supplies, it forced the AVR to pick up all the supply current. When measuring the supply current of just the AOC, it was found to be pulling over 1 Amp of current taking out the AVR’s HDMI power supply.
Now with a down AVR when a different branded device was implemented, it had no way of functioning without the AVR’s HDMI supply. By changing out the AVR and the AOC for the third attempt, all was good and the system responded.
What did we learn? Due to the chain of events that occurred, the integrator was running in circles since this second try with the original AOC caused the AVR failure to occur early on in his troubleshooting.
Remember that the supply current required by HDMI is only .055mA. Many sources provide more than that but, in this case, the AVR would have needed a beefy supply of better than 1.5 Amps to be able to survive the high current load inflicted on it from the first AOC with no external supply. At that point, the damage was already done and no matter how many times he tried it was only when the AVR was replaced when things fell back into place.
Further studies on the high-current AOC were conducted at the front-end electronics (source side) internal power supply, finding exceptionally high current demand. Why the supply did this is still a question.
By dissecting the source headshell, we were able to run an external supply to the device to see if the VCSELs would even operate and they did. So, the problem was in the AOC internal regulators from the start — maybe designed with too low of a required supply current. This could have been caught way before this integrator got stuck.
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