AC86U USB not reading 5 volts

[blitzkrieg]

Hi all

Recently managed to revive my AC86U by replacing MT3125.
It was working well for 5mths~ till I noticed the USB storage isn't detecting and my connected 5V fan is spinning 'louder'.
Tested the USB voltage (both 2.0 & 3.0) and it is not reading 5V, more like 10V~, and obviously fried my storage .
Apart from that, everything else is working OK.

Anybody know which component(s) do I replace/resolder for the USB 5V? (Yes I'm aware AC are EOL, but I'll like to keep it longer)

 

[blitzkrieg]

Upon further probing, both USB2 and USB3 is reading 18~V!

Think i found the culprit, with a burnt mark just above the USB2. Anybody knows what is 'D2' component?

 

[Tech9]

I don't know the number, but this looks like SOT-143 package Transient Voltage Suppressor (TVS) Diode (Dxx on the PCB) used for circuit protection.

Something like this:

https://www.bourns.com/pdfs/CD143A-SR05_12.pdf

Blown means this router was hit by high voltage at some point. 18V on the USB port means you have to check upstream step-down convertor as well.

 

[blitzkrieg]

I don't know the number, but this looks like SOT-143 package Transient Voltage Suppressor (TVS) Diode (Dxx on the PCB) used for circuit protection.

Something like this:

https://www.bourns.com/pdfs/CD143A-SR05_12.pdf

Blown means this router was hit by high voltage at some point. 18V on the USB port means you have to check upstream step-down convertor as well.

Cool, i'll try to get the TVS in 5V, nothing to loose.
Anyways do you know which component can i probe for the step-down convertor? I don't really have an electronics background.
Thanks!

 

[Tech9]

I don't really have an electronics background.

You won't be able to fix it yourself then. There are multiple VRMs on this PCB, you can follow the traces to find which one is involved, but ICs are SMD type soldered with lead-free RoHS solder with around 220C melting point. Some are QFN packages with 16 leads underneath in 3x3mm size. This means you have to have skills and equipment. The PCB has to be preheated, components around shielded with Kapton tape, IC removed with temperature and flow controlled hot air gun, the contact surfaces have to be cleaned with disordering wick and restored with soldering paste, etc. You may need microscope camera. There is barbarian way as well, but with high risk of damaging the traces.

 

[sfx2000]

You won't be able to fix it yourself then

Hey, let them do what they want to do...

 

[wouterv]

I do have an electronics background from ancient times and won't try to repair the router myself....but from my last 20 years work experience I do know some electricians on e.g. offshore ships can do magic and surprise even the original manufacturers by the repairs they manage to do to outdated PLC cards or other professional electronics (often by making one working card out of 2 or 3 failed cards). Magical fixes they are often kind of forced to make due to lack of support (and lack of investments by the ship owner).
So please support and encourage anyone willing to repair their router.

 

[Tech9]

So please support and encourage anyone willing to repair their router.

With no knowledge and proper tools attempting repair will cause permanent damage. I would give it to repair shop instead. For this specific model repair doesn’t make much sense. It’s EoL and has multiple hardware failure points plus unresolved software issues.

 

[L&LD]

Learning has no price. No sense is what you spread, continuously. And markedly opposite of what anyone else may state, or want.

 

[thiggins]

Learning has no price. No sense is what you spread, continuously. And markedly opposite of what anyone else may state, or want.

Uncalled for and unhelpful. Refrain from further attacks or you will get a timeout. I've just about had it with your attitude.