Wifi router does not turn on

Thread Starter

Bassquake

Joined Feb 16, 2018
80
Hi all.

I have an Asus RT-AX55 which does not seem to turn on.

I have the correct power supply at 12v 1a and checked with multi-meter it works and correct polarity. PSU works on other devices too.

When plugged in, no sign of life and no lights turn on.

Voltage is reaching the adapters socket on the pcb.

When power switch is on, I think there's a short somewhere as the voltage drops to 0.

Testing continuity when not plugged in but switch is on, there seems to be continuity across the powers + and -. I also get continuity across the PWR and GND pads marked on the pcb next to the blue capa (see photos). This doesn't seem right. What's the best way to track down where the short is occurring?

What in your experience is likely the component to be causing it? The JWF5J ic? I tried replacing the blue capacitor (16v 100uF) with no change.

Have attached hi-rez photos (Open the images into a new tab to be able to zoom in 100%). Help appreciated.

DSC02661-labelled.jpgDSC02659-labelled.jpgDSC02656.jpgDSC02657.jpgDSC02658.jpgDSC02659.jpgDSC02660.jpgDSC02662.jpgDSC02664.jpgDSC02665.jpg
 
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Dodgydave

Joined Jun 22, 2012
11,233
Something like this I would power it from a 12V psu or battery, and inject the 12V along the input track, using freezer spray and see what melts.
 

Thread Starter

Bassquake

Joined Feb 16, 2018
80
Something like this I would power it from a 12V psu or battery, and inject the 12V along the input track, using freezer spray and see what melts.
Could be an option. Shame its a bit expensive!

Edit: Looks like isopropyl alcohol could be used by watching the evaporation rate.
 
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djsfantasi

Joined Apr 11, 2010
9,151
Maybe a non-contact thermometer would help you find any hot spots. Here at CVS Pharmacy, they are $40-$50 and you can use it as a household thermometer as well.
 

eetech00

Joined Jun 8, 2013
3,814
I have the correct power supply at 12v 1a and checked with multi-meter it works and correct polarity. PSU works on other devices too.
Was the power supply supplied by the router manufacturer?

When power switch is on, I think there's a short somewhere as the voltage drops to 0.

Testing continuity when not plugged in but switch is on, there seems to be continuity across the powers + and -. I also get continuity across the PWR and GND pads marked on the pcb next to the blue capa (see photos). This doesn't seem right.
What reading of continuity to you get? There should be some resistance but not zero ohms.
 

sagor

Joined Mar 10, 2019
894
Between the switch and WPS button, it shows labels for SW then TVS. A TVS would be a surge suppression device, but I don't see it on the board. Maybe it is in the switch or underneath it. It may be possible the TVS is blown (shorted)?
EDIT: On closer look, it may be part of the 3 small components behind the WPS switch. Compare the other TVS devices around the Ethernet ports to this one.
 

Thread Starter

Bassquake

Joined Feb 16, 2018
80
Was the power supply supplied by the router manufacturer?

No, just a standard DC switching adapter. I have bought an official one which will arrive next week I can try.

What reading of continuity to you get? There should be some resistance but not zero ohms.
I get a continuity beep across the PWR and GND pads on the pcb.

I removed the switch and blue capacitor to see if theyve shorted but still get continuity across the PWR GND pads. I seem to get continuity across this component labelled as PC9. Could this be the culprit?
 

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Thread Starter

Bassquake

Joined Feb 16, 2018
80
Between the switch and WPS button, it shows labels for SW then TVS. A TVS would be a surge suppression device, but I don't see it on the board. Maybe it is in the switch or underneath it. It may be possible the TVS is blown (shorted)?
EDIT: On closer look, it may be part of the 3 small components behind the WPS switch. Compare the other TVS devices around the Ethernet ports to this one.
I had a look and none of the TVS pads have components on them. Took a picture of them.
 

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eetech00

Joined Jun 8, 2013
3,814
I get a continuity beep across the PWR and GND pads on the pcb.

I removed the switch and blue capacitor to see if theyve shorted but still get continuity across the PWR GND pads. I seem to get continuity across this component labelled as PC9. Could this be the culprit?
The circled component and tiny component to the left of it. Those might be resistors. Check them with an ohm meter.
Not a good idea to use continuity as a test of on board components. You should use a multimeter (ohm meter).

The negative side of cap (PC12) is open or closed with the blue/red jumper. Interesting the negative side is switched.
 

wayneh

Joined Sep 9, 2010
17,493
Do you mean by feeling if somethings hot? No I don't feel anything getting hot.
Can your meter measure current? It sounds like maybe the PSU voltage is collapsing under load.
Make sure you put the meter is SERIES with the power, not across the poles as you do for voltage.
 

Thread Starter

Bassquake

Joined Feb 16, 2018
80
The circled component and tiny component to the left of it. Those might be resistors. Check them with an ohm meter.
Not a good idea to use continuity as a test of on board components. You should use a multimeter (ohm meter).

The negative side of cap (PC12) is open or closed with the blue/red jumper. Interesting the negative side is switched.
Ohm reading across the PWR/GND pads and the resistors at PC9 is 0.2 Ohms.
 

Thread Starter

Bassquake

Joined Feb 16, 2018
80
Can your meter measure current? It sounds like maybe the PSU voltage is collapsing under load.
Make sure you put the meter is SERIES with the power, not across the poles as you do for voltage.
Ok, I tried this and it keeps blowing the fuse in the multimeter! I only have a 200mA limit.
 

LesJones

Joined Jan 8, 2017
4,170
Are you sure that the polarity of the connector on the power supply is correct for your router ? If it is wrong it could be shorted by a polarity protection diode. It is also possible that if the polarity is wron it could have destroyed the protection diode.

Les.
 

Thread Starter

Bassquake

Joined Feb 16, 2018
80
Are you sure that the polarity of the connector on the power supply is correct for your router ? If it is wrong it could be shorted by a polarity protection diode. It is also possible that if the polarity is wron it could have destroyed the protection diode.

Les.
Yep, have double checked the dc label on the router case, its centre positive, and checked the psu is. Whereabouts would the diode be on the board?
 

wayneh

Joined Sep 9, 2010
17,493
Ok, I tried this and it keeps blowing the fuse in the multimeter! I only have a 200mA limit.
Does it not have the option to use a 10A scale? I'm not surprised that the router draws more than 200mA.
Another approach is to measure the voltage across a low ohms resistor while under load. For instance, finding 0.9V across a 1Ω resistor (in series with the power to the router) would tell you it's drawing 900mA.
 
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