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I'm troubleshooting a router that is missing WiFi and I figured out it's not seeing MT7915 on PCI bus. The router is using MT7975 (RF frontend) + MT7915 (WiFi) combo. I've started checking usual stuff like power rails, enable signals and clocks. 40MHz clock is missing on both chips so it's likely my issue.

However when I checked XTAL circuit I was surprised to see a standard SMD 2520 XTAL but it's connected in a way that makes no sense to me. XTAL input (pin 1) is connected to MT7975 and all 3 other pins are grounded. The XTAL Out pin from MT7975 connects to clock input pin on MT7915 so I assume both chips share the same clock.

How is it supposed to work when XTAL's output is connected to ground?

I've attached photos from 2 different devices using the same combination of chips and the same XTAL circuit.

XTAL circuit
enter image description here

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    \$\begingroup\$ "and all 3 other pins are grounded" Have you measured that these pins are connected to ground, or did you only visually inspect the PCB? \$\endgroup\$
    – Velvet
    Commented Nov 1 at 10:27
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    \$\begingroup\$ Yes I measured it too. I also removed the XTAL and 3 out of 4 pins are definitely grounded. I have no idea how it's supposed to work. This is the first time I'm seeing it. \$\endgroup\$
    – DoubleJ
    Commented Nov 2 at 11:25

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On the last image, it looks like pin 3 (upper-right) has a via to the left of the pad, which I suspect is not connected to ground.

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