Note to Jeff: befw11s4 hangs cured by cryogenics

Repost: corrected unintended long lines. =================

In a previous thread, I mentioned that my befw11s4-based outdoor access point was experiencing the well-known hangs during high throughput and that I had used an SNMP power controller driven by monitor scripts to power cycle the box as a solution. I also mentioned that after a prolonged deep freeze (several weeks at minus 20 degrees F or colder), the unit 'healed' and had not experienced further hangs.

Now that the weather is warmer, I can report that it continues to operate without hanging during high throughput. The nature of the 'repair' is however unknown, and speculation is welcome. The unit remained under power during the severe cold period, and connectivity on the LAN port was uninterrupted, however the radio drifted off channel and clients could not connect until the temps rose to above zero degrees F. for some days. One could imagine some trivial dimensional changes at the pcb level, or perhaps something more fundamental involving changes in capacitor chemistry, IC bonding wire integrity, discrete components changed in value or who knows what in the silicon is at work? In any case the results seem to be permanent and decidedly for the better.

Michael

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Amazing. My only guess is that the wire bonds inside the chips are moving around. When high thruput causes the chips to warm up, they move again.

Did you ever try the 1.52.06 firmware that was leaked out of Linksys?

Note that's it's for the v4 version only and has to be installed using TFTP as the build didn't include proper checksums on each line. I have it installed on 2 units, but have not had the time or inspiration to try it.

Magic?

It was probably slightly above freezing inside the box due to self heating. That implies that condensation was involved, where the radio was basically under water. It's fairly difficult for the radio to "drift" off frequency. However, a water soaked board is going to cause problems. I ran into this problem trying to test electronics over a wide range of temperatures. The worst temperature was the transition zone around the dew point, where water condenses on everything. A good quick test is to freeze a board (not running), bring it out of the freezer to room temperatures, and quickly apply power. The results convinced me that conformal coatings (of various types) and good board cleaning (to prevent ionic contamination) is required to survive such environments.

Yep. It might broken PCB traces inside the multi-layer board. I would tend to favor the wire bond theory. Electrolytics have almost no capacitance left at low temperature, but are usually oversized to compensate. A change in their value might induce some hash on the power supply leads, but I don't think that would cause hangs.

Recycled wisdom: If it works, don't touch it.

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Jeff Liebermann

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