HL2 does not boot at 13.8V, but boots fine at ~12V (startup issue?)

[Miguel Martinez]

Hi all,

I’m seeing a strange startup behavior on my Hermes Lite 2 and I’d like to check whether anyone has experienced something similar.

For a long time I’ve been powering the HL2 from a standard 13.8V amateur radio power supply without issues. However, in the last few weeks the board no longer boots properly when powered directly at 13.8V.

Symptoms:

• When I switch on the 13.8V supply, the HL2 does not complete the boot process.
• The hardware LED just keeps slightly blinking, as if it had little power, and the board never comes fully up.
• No normal network initialization sequence.

What I tested:

1. I tried two different 13.8V supplies (both typical shack supplies). Same behavior.
2. I used a variable bench supply and started at a lower voltage (~11.5–12V).
   → The HL2 boots normally.
3. After it boots successfully at ~12V, I can increase the voltage up to 13.8V (or slightly above) and it continues running without any issues.
4. I also tested with a simple 12V / 500mA transformer supply.
   → Boots perfectly every time.

So the issue seems to be specifically related to startup at 13.8V, not steady-state operation.

This makes me suspect something related to:

• startup transients / overshoot,
• a regulator going into hiccup mode during soft-start,

Has anyone seen a similar behavior where the board won’t boot at 13.8V but works fine if ramped from ~12V upward?

For reference:

• No recent hardware modifications.
• Same cables as before.
• Once running, the unit is fully stable at 13.8V.

Any suggestions on where to probe first would be appreciated.

Thanks in advance.

73,

EA1PYM

[Ed Grafton]

Hermes-Lite2/hardware/hl/hermeslite.pdf at master · softerhardware/Hermes-Lite2 · GitHub

That is the schematic. Check V-out on pin 7 of each regulator. Use 12VDC then 13.8VDC

If you have a thermal camera, you may be able to find the regulator that is stressed.

Ed

[Steve Haynal]

Hi EA1PYM,

I agree with Ed that voltage measurements for each of the voltage planes at 12V and 13.8V in would be helpful. Here are measurement points:

https://github.com/softerhardware/Hermes-Lite2/wiki/Hardware

If you have an oscilloscope, it would be helpful to see if what noise there is on each voltage plane at both 12V and 13.8V in.

73,

Steve

kf7o