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PMX Boot Loop

Edited

Known-issue with PMX Encoder

We have identified a potential issue related to the VBOX internal battery and the PMX encoder that we want you to be aware of in advance.

When the VBOX powers down (e.g., during a quick restart of the vehicle, with yellow status light on the VBOX), it continues to send a very small amount of voltage through BOTH the HDMI and power cables to the PMX.

While the LED lights will be off on the PMX device, the minimal voltage keeps some of the electronics inside the device active. If full power is restored before the power has completely stopped flowing to the PMX, the device will fail to boot correctly. This boot-loop can be confirmed via the LED lights on the device. With full power restored, if the LED lights on the PMX cycle continuously from top to bottom for more than 4-5 cycles, the video stream will not start correctly.

We are very actively and urgently working on a revised power loom to fully resolve this issue, which will of course be sent to you free of charge once it is thoroughly vetted.

In most cases, this is not a common issue - vehicles are not often power cycled for less than the ~30s it takes for the VBOX to shut off entirely, though we strongly recommend checking early on in the installation process that the PMX does not shut off upon cranking the engine, as this would trigger a boot-loop each time the engine starts.

If this is the case, please try to find a more robust power source over which the voltage does not fluctuate when cranking the engine (usually, this means getting power as close as possible in the circuit to the master power switch/battery rather than on an ignition circuit)

In the meantime, the steps below provide multiple solutions.

Temporary Fixes when device is in boot-loop:

  • Turn off the master switch, wait for the VBOX to fully shut down, and then reapply power.

  • If the PMX loses power during engine crank, you need to unplug and re-plug both the HDMI and power cable after the engine is started instead.

Alternative Fix: You can avoid the boot loop issue by using a separate 12V power source for the PMX, not shared with the VBOX.

If you go this route, the power separation only resolves the power back-flow on the power connector - the HDMI connection can still be affected by the back-flow.

It's therefore critically important to use the HDMI cable provided by GPX, as this cable does prevent power back-flow which could trigger the boot-loop. Most other HDMI cables (dozens have been tested...) are not sufficiently shielded and do not provide this back-flow protection.


With all of the above, please note the PMX is a 5V device. We provide all the necessary down-steppers from 12V to 5V, and if you wire the device in your vehicle to a different power source, make sure to keep the down-stepper in the circuit.

The down-stepper has a 2-pin DTM connector, very common in motorsports. 
Applying 12V power directly to the PMX will irreversibly damage the device.