RFI from bad Netgear wall-wart switcher
|May 15th 2012, 15:58|
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I recently experienced a severe case of RFI that blanketed the broadcast band. It was conducted throughout the house, as I could tell when “sniffing” it with an AM radio that was held near outlets.
Coincidentally, our DSL-based Internet connection became intermittent around the same time. I did not connect the two at first. Eventually, however, while in the process of rebooting the router I noticed that its wall-wart switching power supply had become extremely hot. It was too hot to touch – clearly, not the normal operating condition.
After replacing that power supply with a spare from the junk box, the RFI vanished (and the Internet became stable again).
Hooking the bad supply to an oscilloscope revealed a sawtooth waveform on the +5 output, ramping up from 1V to 5V, then dropping and repeating the cycle. An autopsy revealed that the two main supply storage caps – 4.7uF/400V electrolytics – had swollen and leaked out their dielectric fluid. Perhaps these were some of the dreaded Bad Caps that plagued PCs a few years ago.
FWIW, the router is a NetGear RP614v4; and the power module is P/N 330 10096-1. The module is made by DVE, and is model DSA-5P-05; rated 5V/1A.