Is my AC86U toast?

[supe]

I know this thread is old, but I wonder how many rt-ac86u has died with the same symptom, ie only LAN4 led light up.
My unit just died out of warranty and its the same Buck converter MT3125 that's burnt up. This class component is usually expected to last much much longer than just a few years. So this seems to by a systemic issue with this IC or how its being used and may potentially be open to a class action.

 

[OzarkEdge]

I know this thread is old, but I wonder how many rt-ac86u has died with the same symptom, ie only LAN4 led light up.
My unit just died out of warranty and its the same Buck converter MT3125 that's burnt up. This class component is usually expected to last much much longer than just a few years. So this seems to by a systemic issue with this IC or how its being used and may potentially be open to a class action.

Or you could just consider it an RT-AC86U/date of manufacture issue and a part of your overall IT cost and move on.

OE

 

[Tech9]

I know this thread is old, but I wonder how many rt-ac86u has died with the same symptom, ie only LAN4 led light up.

Quite a bit, but this is not the only issue. What I found inside is here. I took home like 10x units, managed to bring back to life 3x using others as donor boards. I believe 4x had blown MT3125, but it was months ago. I kept 1x working unit for my collection, recycled the rest. One failed again after fixing.

 

[huzaimie360]

just want to share my router problem same problem, yesterday i just try my luck to boot up after 4month i throw in the storage room. i plug the power adapter and it boot up after last firmware update that make it brick.. i immediately flash new latest firmware and it run just like normal.. but i noticed the CPU temp is around 92c is it safe or not?

 

[OzarkEdge]

just want to share my router problem same problem, yesterday i just try my luck to boot up after 4month i throw in the storage room. i plug the power adapter and it boot up after last firmware update that make it brick.. i immediately flash new latest firmware and it run just like normal.. but i noticed the CPU temp is around 92c is it safe or not?

Be sure to reset the firmware to its factory default settings before configuring from scratch... to be sure the CPU wait state is enabled (for cooler temp). I had to reset to get this fix when it was released in beta firmware 9.0.0.4.386.41994 awhile back.

Reset FAQ
Reset Button/webUI Restore
WPS Button Hard Reset

92c is on the higher side... the CPU throttles at 100c, so 15-20% less (80-85c) would be better.

OE

 

[huzaimie360]

Be sure to reset the firmware to its factory default settings before configuring from scratch... to be sure the CPU wait state is enabled (for cooler temp). I had to reset to get this fix when it was released in beta firmware 9.0.0.4.386.41994 awhile back.

Reset FAQ
Reset Button/webUI Restore
WPS Button Hard Reset

92c is on the higher side... the CPU throttles at 100c, so 15-20% less (80-85c) would be better.

OE

thanks for the advice i appreciate it

 

[dindin]

Hi guys, on mine the MT3125 SMD looks intact, is it possible that it's still toast?

I am getting this on the console:

MEMSYS init failed, return code 00000001
MEMC error:  0x00000000
PHY error:  0x00000000
SHMOO error:  0x10c00000
0x00000082
0x00000000

... and I was almost certain the NAND went bad, because I read the NANDcromancy: Live Swapping NAND Flash article.
Then I realized it's the LAN4 LED that's lit up, not the power one.

Damn that chip is really, really small.

 

[Darkje]

Figures .. taking down 19 volt to 5 volt. I think for the fun of it I would replace the buck converter. Since it is actually a wonderful router. I changed the thermal stuff and modded the system for full power. And I just like it. I think it is really necessary to keep it all cooled down.

 

[dindin]

Right. It is a nice router after all... if it works!

That makes me wonder though... If the buck converter steps the voltage down from 19v and there is an option to use 12V power supply is this circuit bypassed therefore the converter less prone to fail?
Or maybe it depends on the revision of the router? (https://www.snbforums.com/threads/latest-hardware-revision-of-ac86u.68222/#post-673654)

 

[Tech9]

Damn that chip is really, really small.

You need hot air station and a microscope to replace it.

therefore the converter less prone to fail?

Possibly. It's a switching circuit though and the load current remains the same.

 

[dindin]

Well, I ordered some chips, will see to it once they arrive.
Thanks everyone!

 

[restj90]

hi everyone, reviving this as I saw this very helpful thread while investigating why my 4.5yr old RT-AC-86u has died with the LAN4 led semi-lit up. I then opened up the unit and saw the same photo as earlier in the thread with what I suspect is the MT3125 chip "blown-out". It's quite strange as there were no signs even 1 day before it died that it was overheating or anything. I just woke up to discover burning smell and chip in the state below. HW revision of main board is 1.5 btw. Makes me think if this would be in the planned obsolescence category or just bad component choice?

 

[OzarkEdge]

hi everyone, reviving this as I saw this very helpful thread while investigating why my 4.5yr old RT-AC-86u has died with the LAN4 led semi-lit up. I then opened up the unit and saw the same photo as earlier in the thread with what I suspect is the MT3125 chip "blown-out". It's quite strange as there were no signs even 1 day before it died that it was overheating or anything. I just woke up to discover burning smell and chip in the state below. HW revision of main board is 1.5 btw. Makes me think if this would be in the planned obsolescence category or just bad component choice?

It could be due to a lot of different factors... like maybe the component was made poorly by its supplier... what's your point?

OE

 

[restj90]

It could be due to a lot of different factors... like maybe the component was made poorly by its supplier... what's your point?

OE

just wondering how come this particular device has/had such a defect which seems to have been a widespread issue and if Asus did anything about it? pardon my ignorance if this was already discussed. From all electronic devices I own this is the first one in this day and age to die of a component burning out, just seems to me like a strange thing to happen considering the testing / qc that happens on devices these days. Maybe I was lucky so far but I've owned and played with quite a few electronic devices throughout the years which I also tend to keep for some years and so far this is the first occurrence of such a catastrophic failure I encounter

 

[OzarkEdge]

just wondering how come this particular device has/had such a defect which seems to have been a widespread issue and if Asus did anything about it?

It's been an issue but I doubt you'll determine why, how wide spread, or what ASUS has done about it.

OE

 

[Tech9]

It's common AC86U issue and perhaps result of under specs component used with slight change in application reference design by Asus.

 

[P-Clip]

If only LAN4 led light up means one of the voltage control chip burned, common case for AC86U, simply replace the chip will solve it, costs me about 10USD to get it fix. This chip called MT3125, I got it from Taobao, less than 1USD per unit. I sent my AC86U to a hand phone repair shop with the new chip and asked them to help me to swap it, they charged me about 9USD.View attachment 28790



Before

View attachment 28791




After

View attachment 28792

 

[P-Clip]

If only LAN4 led light up means one of the voltage control chip burned, common case for AC86U, simply replace the chip will solve it, costs me about 10USD to get it fix. This chip called MT3125, I got it from Taobao, less than 1USD per unit. I sent my AC86U to a hand phone repair shop with the new chip and asked them to help me to swap it, they charged me about 9USD.View attachment 28790



Before

View attachment 28791




After

View attachment 28792

So mine was a B to remove.. During cleaning I lost the component in yellow..lol please someone tell me the value. The solder on the original install had a super high melting point...I used a Dremel to remove chip epoxy in center, and used a soldering iron on max.
Air station did not work, huge heatsink on the other side may be why...I did not use constant bottom heat.

 

[P-Clip]

So it's this chip?

View attachment 28797

So mine was a B to remove.. During cleaning I lost the component in yellow..lol please someone tell me the value. The solder on the original install had a super high melting point...I used a Dremel to remove chip epoxy in center, and used a soldering iron on max.
Air station did not work, huge heatsink on the other side may be why...I did not use constant bottom heat.

Is it a 0805 90k?

 

[Tech9]

You may try to find it on the reference design. Specs sheet PDF file here.