What's inside a Cisco Catalyst 9120 wireless access point?

Not just any old WiFi 6 access point, this one's had something special inside... water.
Let's pop the lid off this freshly-drained access point and see if we can resuscitate it.
INDEX
0:00 Index
0:10 Introduction: a Cisco Catalyst 9120 wireless access point
0:47 It got wet
4:35 What's inside?
4:45 Antenna board
5:36 Main circuit board & RF ASIC board
7:37 Found a fault
8:44 Confirming the faulty component
10:26 But what exactly caused it to fail?
10:54 Soldering my first DFN package
11:34 Will it boot?
12:07 Signs of life, but it's not happy
13:57 Another fault found and fixed
15:40 Ethernet port activated
17:19 Conclusions, so far...
No 60GHz capacitors were harmed in the making of this video. Or found, for that matter.

[@sparkyprojects]

There's a YT vid of a guy washing his motherboard in 'scrubbing bubbles' Don't forget that circuit boards are often washed, though i don't know if they use deionised water or something else I don't think the dishwasher could do any worse for your board :D

[@maybehuman4]

Wow. This disaster is the definition of beyond economical repair.

[@AintBigAintClever]

Maybe if it had been spotted sooner it could've been saved, but it had been there all through the school summer holidays while the roof was replaced. We often see stuff turned off during the holidays as that's when electrical works get carried out, but unfortunately that wasn't the reason this time.

[@leadbadger9543]

'it's a bit grim' ... I'll have to use that on a ticket in the future. That roof leak has been going on a while, nearly got barnacles growing in the case. Glad to have found this channel! Good progress getting the brick to talk nonsense on the com port! Now I am curious if they patched the roof before they replaced it, you might need this one for spare parts soon. HA

[@AintBigAintClever]

Felt roof so that wasn't exactly clean rainwater, either. The AP was on the ceiling while the roof leaked, was spotted, complained about, contractors appointed, arrived and the roof ripped off and replaced. I only noticed because it had eventually had a gutsful of being soaked and had fallen offline, but summer holidays is when maintenance gets carried out anyway, so it was only after those that the problem showed up to be a real one. We had another one at another site which was poured out same day by the on-site tech, that one's still running.

[@leadbadger9543]

tougher than they look.@@AintBigAintClever

[@samt4202]

I would check that all the voltages around the replaced MOSFET look good. I have had issues with soldering down that style of package where not all the pins make contact due to excess solder under the chip pushing it out. Also I would take off all the metal shields and clean under them as well. If you have a ultrasonic cleaner I suspect that would do wonders on cleaning the board with some dish soap.

[@AintBigAintClever]

I took off the shields to scan the board, so had a good go under those as well. Good call regarding the MOSFET, I was thinking of probing the two output rails to see if they were swinging properly, but the thing trying to boot threw me.

[@haxorflakes]

pretty interesting looking at trying to find all the faults from water damage. the fact that you even got that far is kind of amazing. with the jibberish on the console port have you tried changing baud rate to see if it somehow is not at default baud rate?

[@Opalinus]

I agree its kinda miraculous you got this working this far. The gibberish in the console will make sense if the correct baudrate and flow control option is set.

[@AintBigAintClever]

I tried all the other baud rates available in Tera Term, no luck I'm afraid.

[@Opalinus]

​@@AintBigAintClever Might be a combination of baudrate and flow control. Tera Term calls the command "setflowcontrol" The same options are also available with PuTTY

[@icesoft1]

@@AintBigAintClever Maybe probe the console output with an 'Intelligent' scope, perhaps it might be able to determine the baud rate, data bits, stop bits, parity, etc... When I saw the gibberish, the first thing I thought was that the terminal speed was mismatched as well... I agree that this thing should never go back into production use - but it's a fun project/challenge to hone your skill set on...

[@SomeFur]

I hope the person who drafted that email has been barred from further mass messages. hahaha

[@AintBigAintClever]

That came from an external Gmail address, fortunately it didn't get circulated widely once it reached us.

[@NightViewHD]

@@AintBigAintClever I really want to read the rest of that letter. It's so entertaining!

[@AintBigAintClever]

@@NightViewHD I thought their initials being E E were rather ironic, given that EE is rolling out 5G across the UK.

[@HDXFH]

This from that storm lol

[@AintBigAintClever]

This was about 40 miles north of that and got its soaking probably a few months before.