RT-AC68U with an antenna base that's hot to the touch?

[GawainXX2]

I picked up a cheap like-new RT AC-68U however I noticed that one of the antennas on it is abnormally warm.

The Antenna connector that's closest to the power switch is abnormally hot to the touch, I'm estimating around 120* Fahrenheit. I pulled the router apart to see if there was anything visually amiss and everything seemed fine.

None of my other RT-68U's have this issue, their connector bases are all cool to the touch when operating.

The board is an RT-AC68U REV 1.80.


What could cause a connector to get hot in this manner, is there likely some sort of a short heating it up?
I plan to stick a temp gun on it as well as try shorting the housing to ground to see if there is a DC current passing through it.

 

[Gar]

Are the other temps ok, for the CPU, etc? Seems like a starting point if nothing else.

 

[GawainXX2]

Are the other temps ok, for the CPU, etc? Seems like a starting point if nothing else.

While they don't seem alarmingly hot, it does definitely seem to run a few degrees hotter then my other RT-AC68U(s). I'll need to use an infrared thermometer on it tomorrow.

As for getting the exact CPU temp, would I Enable SSH and run the following command with putty? cat /proc/dmu/temperature

 

[Gar]

I think it's under tools. My 1900 sits around 75c as I recall.

 

[Grisu]

75 and even up to 80°C in hot summer are normal for 68U.

Mine did not get hot on one antenna, there is a problem.
Use Merlin FW where you easily can watch all temps, CPU, WiFi 2G and 5G

remove this antenna some time to see if it causes the heat and comming down without. Or exchange with another one.

 

[GawainXX2]

CPU idles around 76c
ETH 1 is 71
ETH 2 is 79

The connector base itself is about 46c whereas the others are all sitting around 32c.
This temp was taken without an attached antenna, the temp goes down some when I screw in an antenna as it wicks away the heat some but not by much.

Is this normal behaviour or is there likely some sort of short causing it to get abnormally hot? Is the antenna base an open circuit without an antenna connected or will it still have some current/signal passing through it?

 

[Grisu]

dont know what ETH1/2 are

but again use Merlin firmware where you can watch the 3 temps online with 2G and 5G chips.
Compare them with the others.
44°C maybe within limits, I think the heat is coming from heat sink.

Weak signal can be seen without antenna too, but not good in the long run for the WiFi chips without termination.

 

[GawainXX2]

dont know what ETH1/2 are

but again use Merlin firmware where you can watch the 3 temps online with 2G and 5G chips.
Compare them with the others.
44°C maybe within limits, I think the heat is coming from heat sink.

Weak signal can be seen without antenna too, but not good in the long run for the WiFi chips without termination.

ETH 1/2 are the names for the 2.4ghz and 5ghz radio CPU.

I pulled the housing off the router and let it sit idle for an hour wit the antennas disconnected.

The heatsink on the processors averages 50c while the problematic antenna connector (CON4) temps at 62c! the other two are 40c and 33c.

I think something may be majorly wrong with this connector as none of my other 3 RT-68U's exhibit this behaviour.

I'm going to desolder and swap the antenna mounts on con 4 and 6 to see if the issue transfers with the connector itself as perhaps it's an internal short?

I definitely don't want to run it as-is as I'm concerned it poses a fire risk.

 

[L&LD]

ETH 1/2 are the names for the 2.4ghz and 5ghz radio CPU.

I pulled the housing off the router and let it sit idle for an hour wit the antennas disconnected.

The heatsink on the processors averages 50c while the problematic antenna connector (CON4) temps at 62c! the other two are 40c and 33c.

I think something may be majorly wrong with this connector as none of my other 3 RT-68U's exhibit this behaviour.

I'm going to desolder and swap the antenna mounts on con 4 and 6 to see if the issue transfers with the connector itself as perhaps it's an internal short?

I definitely don't want to run it as-is as I'm concerned it poses a fire risk.

You are definitely adding to the problem by running a wireless router without the antennae. Proceed carefully.

 

[OzarkEdge]

ETH 1/2 are the names for the 2.4ghz and 5ghz radio CPU.

I pulled the housing off the router and let it sit idle for an hour wit the antennas disconnected.

The heatsink on the processors averages 50c while the problematic antenna connector (CON4) temps at 62c! the other two are 40c and 33c.

I think something may be majorly wrong with this connector as none of my other 3 RT-68U's exhibit this behaviour.

I'm going to desolder and swap the antenna mounts on con 4 and 6 to see if the issue transfers with the connector itself as perhaps it's an internal short?

I definitely don't want to run it as-is as I'm concerned it poses a fire risk.

Maybe it's the antenna connector solder joint itself that is marginally soldered and heating up due to resistance. If you can un-solder it, maybe you should just try to re-solder it first?

OE

 

[GawainXX2]

Maybe it's the antenna connector solder joint itself that is marginally soldered and heating up due to resistance. If you can un-solder it, maybe you should just try to re-solder it first?

OE

I'm having a hell of a time trying to get the lead-free solder to flow so that I can suck it up, even with my butane iron. I'm currently looking into tools that would be more effective for this. I'm also buying some SMA-KWE connectors from ali-express.

 

[OzarkEdge]

I'm having a hell of a time trying to get the lead-free solder to flow so that I can suck it up, even with my butane iron. I'm currently looking into tools that would be more effective for this. I'm also buying some SMA-KWE connectors from ali-express.

So, did you try heating it up to re-solder it as it is? Maybe that's all it needs.

OE

 

[GawainXX2]

So, did you try heating it up to re-solder it as it is? Maybe that's all it needs.

OE

Yeah, I tried reflowing it to no avail. It's currently set aside while I wait for the connectors to come on a slow boat from china (literally)

 

[dlandiss]

I'm having a hell of a time trying to get the lead-free solder to flow so that I can suck it up, even with my butane iron. I'm currently looking into tools that would be more effective for this. I'm also buying some SMA-KWE connectors from ali-express.

Something else is heating up that connector anyway. The tiny amount of power flowing to the antenna (usually less than 0.1 watt) would not heat it up.

 

[Squall Leonhart]

a wifi antenna at 30dBm (5ghz band b limit) has a full watt through it, not 0.1
and putting 1w through a dry/cold joint that may have microfractures because of unit heat cycles, yes, 1w is enough to heat it up.

 

[Synomenon]

Just got an AX86U. The antenna connectors on mine all get very hot.