RT-AX86U stuck in boot loop even after recovery

[spindrift]

Not sure if context is related, but shortly after making some changes (swapped out modem, switched to using 2.5G WAN port, changed some DNS settings) my AX86U completely bit the dust. It had been running rock-solid on Merlin with a ton of scripts and apps for a year prior.

Things I tried, in many different orders:

- Recovery mode (reset button 5sec. before/after power, slow blinking light) with both ASUS Firmware Recovery tool (errored) and tftp (succeeded)

- WPS recovery mode (succeeded in bringing up firmware upload page)

Both on static IP 192.168.1.1.

In all cases I tried uploading:
- newest stock ASUS firmware
- older stock ASUS firmware
- even the newest Merlin

After a successful recovery (tftp completes and I reboot, or router reboots itself after web page upload) it goes right back to cycle of:
- power light comes on
- LAN light comes on
- LAN light goes off a few secs later
- power light goes off a few secs later

In that period pings will hang until they come back unreachable, and the LAN status of whatever it’s attached to will show the connect/disconnect accordingly.

It would be a damn shame to lose my favorite router ever + vital infrastructure box just a few months after being out of warranty, but that’s what I get for buying used I guess.

Any other ideas before I throw in the towel?

 

[eibgrad]

Perhaps try a hard reset. Works w/ my AC68U.

1) Power OFF the router.
2) While holding in the reset, wps, and wifi buttons, power ON the router.
3) Wait for the power LED to flash *quickly* (usually takes 10-15 seconds).
4) Release the reset, wps, and wifi buttons; most of the LEDs will now flash
once, in unison, and the router will reboot.
5) Power OFF the router.

P.S. I'm not positive the hard reset alone will be sufficient, but it may be. If not, try updating the firmware again, but using tftp.

 

[bbunge]

Hard reset is done by holding the WPS button, turn power switch on, power LED will come on - keep holding WPS button until power light goes off, turn off power and release WPS button. This is the procedure for the AX86U.
Note: It has been observed that sometimes this does not work to clear all settings on some AX86U's.

 

[spindrift]

Thanks for the advice y’all—the plot thickens.

When I tried to do the hard reset this morning, the router had progressed to not turning on *at all*. That’s when I noticed that the blue light on the power brick (not the router, the power brick) was flashing on and off.

I suspect this to either be a relatively good sign (it was the cheap power brick failing, not the expensive router) or a pretty bad one (the brick is indicating an electrical issue inside the router).

I’ll try and rule out the brick by looking for an appropriate alternate power source around the house, but otherwise I imagine I’m looking at a disassembly and hunting for burnt capacitors and the like.

 

[spindrift]

Now that I look at it closer, the power brick light isn’t flashing, it’s *rapidly dimming* and then what looks like quickly restarting itself. It stays solid blue when not connected to the router. This seems to further indicate an electrical issue—some component overheating. I also found a similar 12V@3A brick and it still wouldn’t start.

Bummer. I’ll keep investigating. Sorry for swamping anyone’s replies, but maybe the thread will help future generations.

 

[Analog-1]

Sounds like the voltage regulator in the router has failed. Known weak spot on some models perhaps due to heat.

 

[bennor]

That’s when I noticed that the blue light on the power brick (not the router, the power brick) was flashing on and off.

Power brick light? Is the power adapter the original power adapter that came with the Asus RT-AX86U or a third party/replacement adapter? Not sure about other countries but there is no "light" on the several Asus router power adapters that I have. Its just a typical wall wart with no power indicator on it. Rather the router indicates if it is receiving power via the router power LED.

If it is a third party or replacement power adapter then its possible the power adapter itself is going bad.

 

[spindrift]

Sounds like the voltage regulator in the router has failed. Known weak spot on some models perhaps due to heat.

I’ve seen a bunch of posts on that related to the AC86U, but couldn’t dig up any schematics info / voltage regulator IC posts about the AX86U. Do the symptoms I mentioned specifically suggest that chip? I have nothing to lose, so before I post it on eBay for parts am willing to make it a learning experience.

 

[spindrift]

Power brick light? Is the power adapter the original power adapter that came with the Asus RT-AX86U or a third party/replacement adapter? Not sure about other countries but there is no "light" on the several Asus router power adapters that I have. Its just a typical wall wart with no power indicator on it. Rather the router indicates if it is receiving power via the router power LED.

If it is a third party or replacement power adapter then its possible the power adapter itself is going bad.

Good call; I got it used in box, but it’s possible it’s not the stock adapter. I did try it with a different brick, but I had to use some plug adapters for it to fit, which puts a kink in my confidence level that I’ve truly ruled the power source out.

 

[Analog-1]

I would at least try another known good power brick before you dump it for parts. Problem with Asus routers is there quality control during assembly mostly when it comes to heat sinks and cooling. Some are good to go others over heat and fail in time.

 

[spindrift]

I would at least try another known good power brick before you dump it for parts. Problem with Asus routers is there quality control during assembly mostly when it comes to heat sinks and cooling. Some are good to go others over heat and fail in time.

WELP, it was the power brick!! Thanks for the encouragement to keep trying.

Funny how easily things flip from being pissed at ASUS to impressed they made a router that can survive a failing adapter and a couple dozen reflashes of varying quality.

Now to reverse my over-eager teardown and get the PCB back in the case…

 

[spindrift]

The “lesson to future generations” here is:

- The power required for recovery mode and normal operation seems to be different. A bad AC adapter may be able to handle the former but not the latter.
- If you can successfully flash new firmware (through either tftp or the web interface) then it’s probably not a lost cause, even if it keeps rebooting afterwards.
- Do everything you can to rule out the AC adapter before assuming it’s a faulty component, and ESPECIALLY before opening up the case.