Component identification

[James92TSi]

Recently I had some kind of power spike (still trying to figure out exactly what happened) which burnt out several network devices including my EVL3.

All of my network gear is protected by a double-conversion Liebert GXT3 UPS. I think the issue may have been POE related. The POE function of my switch no longer works (but it still passes traffic) - and I lost the EVL3 and a POE wireless access point which were both connected to the same POE switch. POE was enabled administratively on all the ports, which is generally a non-issue since non-POE devices should never negotiate to receive power. Anyway...

The EVL3 would still communicate with the alarm panel, however its network port was dead. LEDs would alternate red and green. Red (oper) flashing for powered/normal, and green (keyb) flashing indicating good communication to the panel, but no IP address. Link/Act LEDs near the network port both dark. I worked with support to verify the hardware was in fact dead.

I've replaced it with an EVL4 and my system is back to normal.

However, under magnification I noticed an obviously damaged component near the network port. Appears to be a SOT-23 package surface mount device. It is marked 21S VO and I cannot seem to definitely cross-reference that to a replacement part. Might be zener diode, might be transistor, or any other wild guess.

Pics:



Top-left corner of this pic, above the ethernet port.



If anybody can tell me what this is, or provide schematic/BOM/whatever engineering data, that would be super cool.

I basically want to fix it and keep it as a spare if I can. No idea if the visually blown part is the only thing wrong with it, but I have a hunch it's a protection diode that did its job.

Thanks!
James

[James92TSi]

I desoldered the damaged component and an undamaged one next to it for testing/ID. Found it is a dual series diode. The undamaged one passes current pin 1 to 2 and 3 to 2, and not in reverse, which lines up with the schematic of: http://www.onsemi.com/pub/Collateral/BAS21SLT1-D.PDF



The damaged one passes current pin 1 to 3 (but not 3 to 1), and is open between 3-2 and 1-2 in both directions, so its second diode is blown out. This lines up with the visible damage.

I'll try replacing it (18 cent part), and if it works again, great... if not, the spike (or whatever) might have passed along to the ethernet chip which means it's probably dead to me.

In a non-EVL-related note, my Ubiquiti WAP that died in the same event has a blown POE powered-device chip, LM5072 MH-80.





All told, about $4 worth of parts to attempt repairs on both pieces. I"m a bit more confident about the WAP than the EVL, but maybe both will be resurrected.