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[Solved] Need Help

I need, what should probably be some basic electrical help, but this is kicking my A*S*S.  My setup is shown below, but in short it is a Pi 4, Moitessier HAT, & MCS Board.  The MCS Board has three power inputs: 1) constant +12V-28V, 2) on/off +V, and 3) ground.  The MSC Board supplies power to the Pi.  Via a hardware switch, the on/off +V signals the MCS Board to power up the Pi and the MCS App to shut down the Pi before the MCS Board powers off.

I also have an Atolla powered USB 3 Hub, a bank of 4 relay switches (currently unpowered), and a AIS/VHF Antenna Combiner (currently unpowered).  A Wifi dongle, keyboard dongle, and two USB cables routed to ports on the exterior of the case are plugged into the USB Hub.  The USB Hub is supplied 5.3V (verified) by a Binzet DC 12V-24V to 5V Transformer Converter.  The whole thing is powered by an old 19V Dell power supply.

Everything powers up and functions, even the relays and AIS/VHF Antanna Combiner when the fuses are in place.  My problem is that the hardware switch will not shut down the Pi before the MCS Board powers off.  I've traced it down to the USB Hub.  
  • USB 3 cable into Pi: Plugged,     5V power lead into Hub: Plugged:     Pi will not shut down.
  • USB 3 cable into Pi: Unplugged, 5V power lead into Hub: Plugged:     Pi will shut down.
  • USB 3 cable into Pi: Plugged,     5V power lead into Hub: Unplugged: Pi will shut down.

When I test the on/off +V lead to the MCS Board, if both the USB Cable and the Hub are plugged in, it gets 19V when the power switch is on, and 4.5V when the power switch is off.  If either the USB cable or the Hub are unplugged, the on/off +V goes to 0.

Things I've tried:
  • I desoldered the red +5V wire from the USB 3 cable to the hub.  This didn't work.  The Pi would shut down properly, but the USB dongle quit working even though it looked powered up.
  • I soldered a diod rectifier between the USB 3 cable and the hub.  The USB dongle worked, but the Pi would not shut down.
I am at my wits end.  The power from the Binzet transformer is backfeeding the Pi through the USB Hub.  The voltage measured at the MCS on/off +V when the power switch is turned on is 19V and goes to 4.5V when the power is switched off.  I'm guessing the Pi is causing a voltage drop from 5.3V to the measured 4.5V.

Here is the USB Hub I am using:
and the Binzet Transformer:

Please...Anyone who can help me with this, I'd be in your debt.

[Image: SV-Rotarran-OpenPlotter-scaled.jpg]
I figured out the problem...When the power button was switched off, the 19V power was cut to the fuse block, turning off the power to the USB Hub, but because the Pi was still powered through the MCS Board, the USB Hub was still receiving 5V through the Pi's USB 3 port.  This power then back-fed through the Hub's power lead, through the Binzet DC Transformer, to the fuse block.  The fuse block would then show 5V, which was being sent to the on/off +V to the MCS board, keeping the Pi alive.

I fixed it...I added a 5A Schottky Diode between the fuse block and the Binzet DC Transformer which is powering the USB Hub.  This prevents voltage from backfeeding, allowing the on/off +V to the MCS Board to go to Zero, signalling the MCS App to shut the Pi down.

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