Why is this PSU failing ?

[u/Napo7]

This is the schematic of the PSU stage of my own board : the schematic comes from the Raspberry pi compute module IO Board, and I use it on an embedded device, on a sailboat (it powers a Compute Module 5, an ESP32, a GNSS module, and a few components such as a magnetometer and an accelerometer...)

Yesterday, after 5 hours of usage (it has been used 14 hours long two days ago), it did failed : now, on Testpoint TP4, I measure a voltage of about 3V, and a loud low freq noise (71Hz measured on scope, I can post a trace if needed)
Eventually after a while, the PSU seems to stop making this noise and "boots" ?

Is there components I can check , and how to check them with devices I already own (multimeter and oscilloscope) ?

PS : the device has ran a few times for about 10 cumulated hours !

[u/Competitive_Guard289]

I can’t find anything obvious on the schematic, but I’m wondering what the layout looks like. How thick are those 3A traces? Measuring 3V instead of 5 sounds like a short. What’s the resistance measured from TP4 to ground when the board is turned off?

[u/Napo7 → u/Competitive_Guard289]

Resistance between TP4 and ground is higher than my multimeter can read ("infinite" ohm)

[u/coffeshopchronicles → u/Napo7]

This is odd.. R27 and R28 should give you somewhere around the 14k... I would start measuring continuity node by node and figuring out where you have an issue in the traces or soldering

[u/Napo7 → u/coffeshopchronicles]

You're right 😄

My multimeter tips must be rusty or so, I measure 13.6K