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AP55c - took it apart to see what is wrong with it?

IanMorehouse

My AP55c has been giving issues on the 5ghz band, so I decided to take it apart.

Yes, I checked it is out of warranty.

I found all these strange marks on the PCB that look like water stains. They could also be solder fume residue. There is a liquid on the heatsinks between the chips and the fixed pads, looks like some form of oil.

There appears to be corrosion around some of the joints. I can only think if they are water stains that they are condensation points. At times around here the humidity hits 80% inside, but why only the AP55c which sits on a stand in the middle of the room and why only the 5ghz channel is affected? Anyway it looks like I am up for a replacement whuch more than likely will be an AP55.



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  • 0

    Ian, what's the serial number mate?  I've got an AP55c here as well, it's a fairly new acquisition for me, but I'll be happy to bust it open and check what it looks like as a comparison.  Any chance you can get fairly clear close up pictures and post them for us to see please?

    ==

    When in doubt, Script it out.

  • 0 in reply to AzRoN

    Hi,

    thank you for responding.

    Serial number is a4002f8cf8af908

    Photos to come.

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  • 0 in reply to AzRoN

    Hi,

    the photos from the AP55c.

    www.pbase.com/.../ap55c

    I should have used the tripod for a better quality result. Anyway you can see the marks on the PCB and the stuff on the heat sinks. It is a liquid of some sort.

    The replacement will be an AP55 so I can put it on the shelf next to me. This one cost over $500 (AUD) when I bought, so a bit annoyed at the failure.

    Ian,

    home UTM 9.x running in ESXi 6 e3-1275v2

    AP55c and AP10 (courtesy Astaro)

    Three other UTMs, SUM and SFM in hibernation

    XG 15.x MR3 in hibernation

  • 0 in reply to IanMorehouse

    Sadly, those "water stains" are normal... It's left over flux from the modern no-clean soldering process. Whoever Sophos is using for a PCB manufacturer is clearly doing a poor job, that should have never made it past quality control. If you want to make it look pretty, just take some 90% isopropyl alcohol on a lint free cloth and you can clean it right off. It may correct the 5Ghz issue as well given it's right on the RF traces. Just make sure you let it air dry for about 15 minutes afterwards.

    As for the oil on the heat sink, it looks like Sophos is using a machine applied thermal paste which is not ideal. They really should be using a thermal pad instead as they don't leach liquids, something that can be huge problem in PCBs that are used vertical (just like a Wifi AP). Again, if you want to clean it up just use some alcohol and remove all traces of the oil and old paste. Find a nice thermal pad from your favorite electronics store, cut to fit and you should be back in business.

  • 0 in reply to Dlabun

    Hi Dlabun,

    thank you for the detailed expanation.

    I cleaned te PCB up, but that had no affect on the issue with the 5ghz, but apears to have made a difference to the 2.4ghz, more devices are hitting 144mb/s connection.

    I thought I had found another reason in the AP configuration on the UTM and that is a feature I had not seen before, U-APSD, which unschedu;ed automatic power saved delivery. I have disabled that feature on all SSID's but again no affect. Maybe I need ot restart all the wifi devices to see that has any affect.

    Ian,

    home UTM 9.x running in ESXi 6 e3-1275v2

    AP55c and AP10 (courtesy Astaro)

    Three other UTMs, SUM and SFM in hibernation

    XG 15.x MR3 in hibernation

  • 0 in reply to IanMorehouse

    More experimentation today. The settings I identified above have no affect.

    I installed a tp-link dual band usb wifi device, 2.4ghz quick connection and maintains connection. 5ghz starts and quickly disconnects.

    Other little issue is I get better and more consistent throughput from an AP10 down the other end of the house, through two thick metal doors and a silvered mirror let alone lots of plaster.

    So conclusion, this AP55c is dead and should be buried.

    Update - having said that about throughput the AP55c 2.4ghz now connects at a reasonable speed 130-144mb/s.

    Ian,

    home UTM 9.x running in ESXi 6 e3-1275v2

    AP55c and AP10 (courtesy Astaro)

    Three other UTMs, SUM and SFM in hibernation

    XG 15.x MR3 in hibernation

  • 0 in reply to IanMorehouse

    That totally stinks the 5Ghz didn't come back to life. Odds are the 5Ghz radio was shorting out from the flux and the cumulative damage was too extensive. Hopefully Sophos takes a hard look at their quality control program and fixes these avoidable manufacturing issues. 

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