Repair a awus036nha usb wifi adapter

[Delchrys]

Hi all,

After accidentally frying my wifi usb adapter I'm now trying to fix it.
I'm having trouble identifying a IC that is blown in the process.
Can someone point me in the right direction.
Its part U7 which has numbers on it C1=H6 S4J

[amyk]

RT8020GQW

[Delchrys]

Geez thanks how did you figure that out?

[wraper]

It's how Richtek marking looks like. Device code usually is first 2 digits/letters + 3rd symbol like "=" or "-", or if there is a gap after first 2 symbols, then simply first 2 digits/letters.

[Delchrys]

I have another awus036nha module which uses a different code on the chip tho....
Do I need a 100%same replacement? Because I'm looking at rsonline which my company has a contract with and they don't have them.

[Delchrys]

Any chance this burned chip prevented the rest from breaking? Or is it likely I damaged more?

[Delchrys]

Does the C1 mean it's a 3.3/1.2V type?
So a RT8020CGQW?

[amyk]

Look at the datasheet. CGQW is C4=.

[tom55]

Hi

Recently blown up my AWUS036NHA card after plugging in Y-USB cable into QC3 charger that exploded, taken it apart to find the RT8020GQW gets extremely hot. Removed it from the board and checked the 1.2V / 3.3V output resistances, they were very low about 1.5ohm / 5ohm and it looked like AR9271 is dead too.

Next tried supplying 1.2V and 3.3V from old laptop motherboard, first connecting only 3.3V - AR9271 got also too hot and i measured 2.5V on 1.2V output so i thought there is internal short and this killed it.
Powered off the board, checked resistances at 1.2V there was still 1.5ohm but on 3.3V it went to 9ohm.

Then tried connecting both supplies and powering up the board, this time AR9271 was slightly warm, I took USB cable, masked 5V pin with insulating tape, plugged it in to my router and to my surprise the card was detected and firmware loaded. I enabled the interface and connected without problems.

So even it looks like the wifi chip is dead because of low resistance it doesn't necessarily mean it is. It appears to have strong internal protection mechanism against surges and overvoltage conditions, that are disengaged once the proper power supply is restored.

After removing temporary supplies I checked resistances again and now they are about 142 / 153 ohm

[tom55]

Update

It only looked like at first there is some sort of protection inside AR9271. Turns out there isn't.

Part of the chip got fried, there was a consumption of about 0.5W from wall and chip getting slighthly warm.
Even in such state it was still useful.

But after having problems with RT8020 replacement and one more dead power converter i managed to solder another RT8020 with good connections.

Plug in card to laptop, it works. Plug in to router it works in both AP/STA modes.
But when i tried to load it on my modified router firmware, STA mode kept crashing no matter what.

Then, after some debugging it was discovered it works fine in AP mode accross entire range 2192-2887Mhz, however, when changing channel from approx. above 2550 Mhz to lower channel it would crash.
Same way it was crashing in STA mode, because in STA mode the card first scans entire range and then goes to selected AP channel. To confirm i set another AP at 2712 Mhz and the Alfa in STA mode connected without issues.
Then it was also noticed the TX/RX rates are not full with alfa on 2.4channel in AP mode and laptop connected to it. There was RX 108mbps and TX mostly 150mbps but dropping to 135 and 121mbps.

Next came the idea to warm the card with 150 celsius, after just 20 seconds, both rates synced at 150mbps stable. It cooled down, rates dropped.
Heated again, this time directly on AR9271, rates good again, tried changing channel to 2700mhz and back to 2412mhz while chip is hot and there was no crash.

I thought maybe solder got ruined from all the heat during RT8020 replacement attempts and tried to resolder all the elements and ar9271 contacts.

After this the card kept working and switching channels to and from high band worked without crashes.
But i noticed the txpower was very weak. One or more pins on SE2576 amp lost contact, i fixed it and the power was good again.
But the crashes came back as well.

At this point i was in doubt on what to do next:
Seems like heat on AR9271 restores everything to work fine, so it could be damage on it.
But then again, with SE2576 disabled switching channels worked fine.

I had TL-WN722 with same chip. Took off both AR9271, and put the one from tplink to alfa.
The problem with rates and channel switching remained. Ordered SE2576 parts and waiting now to arrive.
If replacing that doesn't help then it will probably be the most annoying capacitors/inductors mess...

The resistances of 3.3/1.2 power paths on alfa were about 159/143 ohm. After too much heat got to it during RT8020 changing they dropped down to 28/12 ohm. And during further repair attempts they rose to 60/20 ohm.

This is all bad. With good chip from wn722 on alfa, i get about 1kohm on 1.2v path and climbing up to 230kohm on 3.3v path. This may not be final good values depending on type of failure of SE2576 or capacitors.

The consumption from wall of the alfa card is 0W after ar9271 changed.

The chip taken off alfa had only 17ohm on 1.2v. Since it was still working i decided to put it on tplink.
After soldering, it had 16ohm/46ohm. WN722 works with chip from alfa, even though it is partially fried and having such a low resistances, TX/RX rates synced at 150mbps and kept stable, also no crashes when changing channels accross 2.2-2.9ghz range on my customized firmware.

So, the chip seems fully usable, with small dowside it consumes some extra power and generating a bit more heat.

[tom55]

rates problem as well as scanning accros entire band was solved by replacing faulty inductor on 1.2V output. with iperf tested it was about 100mbps both directions, as usual.
it works for several months now 24/7