Polaroid 6500 Sonar Problems

I am attempting to interface a Polaroid 6500 Series ranging module with Instrument Grade Transducer (round) to the MIT Handyboard. Data sheets can be
found here:
I have soldered in a 0.1uF capacitor in the C7 position and have hooked up and verified the circuit given here, (using the software provided here also):
The problem I am having is that the 5401 diodes got extremely hot and started smelling a bit. Also, the values displayed on the handy I measured the voltage drop across the diodes and it was about 4.2 volts. So then I decided to bypass the 5401 transistors and hook the 6500 module directly up to a 2A, 5.2V DC Supply. Monitoring the current, I noticed that the module was pulling 2A all of the time! The polaroid data sheet says that the module pulls 100mA of standby current and 2A during transmit, so it appears that the module is always attempting to transmit. Any advice on how to get this working?
Thanks, Brian
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