So, here is some potential insight on the problem of no rear channel recording, despite the A130 Pro 2-ch camera announcing "Two Channels Recording" when it starts up. Maybe this is helpful for others, maybe it is helpful for VIOFO-Support, or maybe not.
I've spent the past few days working on installing the A139 Pro 2-ch in my car
using an external battery back as a power source for parking mode instead of running parking mode from the car's primary battery as described in this thread. This set up runs nearly completely on 5v wiring, so I'm using the HK3-C wire without the 12v to 5v regulator box that it came with. Below is my attempted wiring configuration that did not work:
The main goal for the above wiring configuration is that the LiFePO4 power station only operates within a specific temperature range (not below -10c and not above 45c). Thus, the Power Station can't directly power the dashcam when it is extremely hot or extremely cold outside, so it needs to be bypassed. This is where the relay comes in - it allows the camera to be powered directly from the car's electrical system while the engine is running and switches over to the power station for parking mode recording when the car is shut off. If the air temperature is beyond of the operating range for the Power Station, you'll get driving recording, but not parking recording. This is an acceptable tradeoff to me for not placing additional strain on the car's main battery. The car's primary AGM battery is expensive and require a software reset in the car's computer system when you change the AGM battery, but this function is only available at the dealer for a significant service charge. Hence my interest in a secondary battery for the dashcam. In addition, the River 2 Power Station automatically activates the 5v USB output ports when the car starts, but it doesn't automatically activate the 12v port when I start the car. These are the two reasons why I created a 5v wiring scheme instead of using a 12v wiring configuration.
I ran into some challenges as the Viofo USB utility outlet adapter provides about 5v25 whereas my Power Station (an EcoFlow River 2) provides only about 4v90 through its USB output ports. This voltage difference caused the A139 to react poorly. It would reliably switch from "drive mode" recording to "park mode" recording when the engine shut off, but it would not come out of parking mode recording AT ALL after the engine was turned on again. To get the Viofo A139 Pro to turn back on, it would have to be completely powered down first. I spent some time unsuccessfully attempting to cycle it into and out of parking mode with the relay before I abandoned the wiring configuration above and adopting the wiring configuration shown below:
This new configuration without the relay "seemed" to work well afterward: The A139 Pro 2-ch camera consistently announced "two channels recording" when I started the car, as well as "parking mode recording" when I turned off the car, but it wasn't until I actually looked at the memory card that I noticed that the rear camera recordings were missing (the camera was actually writing both front and rear facing video files on the card before I attempted the first wiring change). Despite the missing rear channel recordings on the memory card, I could still see the rear camera video feed in live view from the app.
This seems to replicate the exact symptoms reported at the start of this thread.
In order to solve this problem, I did the following things:
1) with the car running, the camera powered up, and the rear camera connected, I used a straightened paperclip to press the "reset" button on the camera itself.
2) When it was done rebooting, I used the app and clicked the "Reset Camera Setting" function down at the bottom of the settings screen.
I had previously tried using just the "Reset Camera Setting" in the app, but the rear camera recordings still weren't being written to the memory card, despite the camera announcing "two channels recording." I could still see the rear camera feed using live view in the app.
Performing BOTH reset actions in sequence solved the problem and allowed the camera to once again create video files on the memory card from the rear camera. Thus, it is my conclusion (perhaps incorrect) that the problem resulted from either A) the difference in voltage output between the Viofo USB adapter (5v25) and the River 2 USB output (4v90) when the relayed switched power sources for "drive" mode vs "parking" mode, or B) the lower voltage from the River 2 USB port combined voltage drop from the 9-foot wire run to the camera resulted in too low of a voltage for the camera to operate properly.
Since resetting the camera and using the second wiring schematic shown above, the camera is behaving exactly as expected again, recording both front- and rear-facing videos on the memory card. This seems to rule out potential problem B) from above. Thus, I'm thinking the problem of no rear video being stored on the MicroSD card might be the result of low voltage during parking mode contrasted with potentially higher car voltage once the engine starts again. Just a guess, but I can't come up with any other explanation at the moment.
I have a USB-C voltage tester on order so I can measure the actual voltage that goes into the camera and see how much voltage is being lost in the 20ga wire from HK3-C hard wiring kit. I suspect this is why the voltage regulator that I removed from the wire outputs 5v25 - it accounts for the voltage drop in the long cable run to the camera.
I'm using a SanDisk Max Endurance C10, U3, V30, 4K UHD, Micro SD 256G card. Dashcam Firmware is VIOFO_A139P_V1.1_0629.
Hopefully, this helps others track down issues and get their camera working again.
