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We noticed a problem with power sequencing on our board: if the negative rail was turned on first the positive rail would get pulled to -0.7V and latch there, even after the batteries were connected. We installed LEDs on both rails so that we could make sure they were both working properly, but we are worried we may have damaged the chips. Operation is very intermittent. All of the connections ohmed out as connected using a multimeter, and multiple checks of every connection has verified that the board matches the schematics. When testing with the app, the signal levels are usually constant at approximately 80dB. every once in a while the level will drop slightly and the ~21kHz tone will appear momentarily before disappearing again. We tried probing with the scope, but got inconclusive behavior. Most of the time the output would have the appropriate spectral content, but at very low amplitudes (output was in the mV). Occasionally the antenna amplifier would start oscillating and outputting a ~140kHz -12V to 12V square wave. Any ideas? At this point we have "detected" the signal once for about 3 minutes on Thursday, but have had no luck since.
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