When the uplink module connector is not alligned properly with the main board connector the result could be a short of the power rail.  This short will prevent the power supply from coming online and the EX switch may not power up.

When the EX switch is plugged in it will not power up.  

One of the checkpoints is the uplink module.

Try the following:

•   If you have a spare uplink module disconnect the EX switch and plug in the spare uplink module.  Connect the EX switch to a power source.  If the EX switch powers up and boots properly then inspect the suspect uplink module for bent pins.

• Check the pins on the suspect uplink module.  If the pins are bent then straighten them out or reinsert into the EX switch when it is powered down.  If the EX Switch still does not power on then contact Juniper Support.

If the uplink module connector is not aligned with the main board connector, or if there are bent pins on the uplink module, this can result in a short circuit of the power rail which will prevent the power supply from powering on the device.

2020-07-17:​  Article reviewed for accuracy; no changes required.