Fix for AC Infinity Aircom T8 with weak or low USB fan output

[Per Hansson]

A friend came over with this device today that I actually looked at previously at his place but did not really have any tools with me at the time to properly troubleshoot it.
It is a cooling system for your home AV receiver setup with 3 built in axial 12v blower fans and that part worked fine.
It also has two USB ports at the rear that follows the voltage curve of the main fans.
So you can connect up an external 5v USB fan and cool another unit that way.
I recommended him to just buy a Noctua fan for the job, he got a NF-F12 5v and that worked fine for about a year or so.
But then the Noctua fan failed to spin even at the maximum setting, the voltage was only 2.2v at max.
I traced the circuit a bit and found a significant ripple at dropper diodes D1 & D4 of around 10VAC!
After some further tracing I found bad capacitor C4 that sits at the 5v USB output.
Infact it had ESR over 140Ω which is the maximum my meter can read! But fear not, my Agilent U1733C has no such limits and showed an ESR of 330Ω at 100Khz
I was unable to identify the manufacturer of this capacitor, its only markings where: LM MR 10uF 35v 105°C
I put in a Nichicon PW 10uF 50v capacitor in its place, the ripple measured 0.5v after this and the Noctua fan spun up just fine

The rest of the caps in the unit are of brand LSCON, They did seem to measure fine in circuit so I left them alone for now.
I linked their datasheets below, they also exist on Paullinebarger
LSCON SL 100uF 16v 105°C
LSCON LL 220uF 16v 105°C (might have been 25v)

[momaka]

Re: Fix for AC Infinity Aircom T8 with weak or low USB fan output

Nice work documenting the repair!

Up until this moment, I didn't even know such cooling devices/units existed.

I guess bad caps can strike in anything.
Judging by the inductors and toroids on the board, there are buck regulators there? If so, probably worthwhile to replace all caps on the input and output of each buck regulator at some point.

My parents also have an AV system in a cabinet... but it was a cabinet from an old CRT TV, so it has some depth to it and overall is quite roomy inside. So even in the summer, it never gets too hot. Also, the "AV system" they have is just one of those Panasonic 5-disc CD/DVD units with a built-in 5.1 amplifier system. It's all class-D stuff in there, though, so it hardly kicks out any heat, even under heavy load. Nowhere near a Hi-Fi at all, but it gets the job done.