[FS#100] PCengines APU 2c4 instant power-off issue

[LEDE Bugs]

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FS#100 - PCengines APU 2c4 instant power-off issue
User who did this - Bluse-Blue (Bluse)

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Hi all,

As we have performed several test with an oscilloscope attached to the APU I hereby report out results:

setup-A: 1x APU 2c4 with  two Mikrotic mPCIe WiFi cards (1x R11e-2HPnD & 1x R11e-5HnD).

results:
	-configuring two APs, one on 2,4Ghz  and the other on 5GHz we can trigger the power off issue in seconds by having a client connected to each AP and just performing a cat /de/zero download via ssh on each client
	-the oscilloscope is attached on the 12V line via an 1Ohm measurement shunt
	-the voltage monitoring across this resistor are similar to the current flow (1V equals 1A)
	-the picture shows the last microseconds before the board shuts down, the overall power consumption is the delta between the two voltage lines y1 & y2, which is about 2V so respective 2A… meaning the whole APU toke 12V * 2A = 24 Watt while the two downloads are running


setup-B: 1x APU 2c4 with  two Mikrotic mPCIe WiFi cards (1x Compex WLE200NX & 1x R11e-5HnD)

	results:
		- same AP & client setup as before with cat /dev/zero downloads via ssh
		-no power shutdown from APU and 1,6A load on the 12V line

		-in addition we added an 120GB SSSD to the mSATA port as another power consumer and loaded it with some dd fileoperations while downloading
		-the overall power consumption increased to 2A as shown in the next plot, but the APU did not power of and kept running finr




Conclusion so far:
	-it seems that the Mikrotik R11e-2HPnD WiFi card does overload one of the internal 1,8V, 3,3V or 5V rails and triggers a power shutdown of the board
	-a COMPEX WLE200NX in combination with the Mikrotik R11e-5HnD and an mSATA works at the same overall power consumption just fine
	-also the less power hungry card Mikrotik R11e-2HnD Wifi in combination with the Mikrotik R11e-5HnD and an mSATA works fine


Greetings from Berlin
Thomas

ps: … we do now rebuild our APU setup to replace the high power Mikrotik R11e-2HPnD cards with R11e-2HnD once.

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https://bugs.lede-project.org/index.php?do=details&task_id=100#comment384