I have purchased and assembled, with no short-cuts, the H-Bridge Motor Driver by Anson Bao and find that there is no LO output on either side with VCC = 12 V, 50% duty PWM, and EN at 5 V. Thus, the bootstrap function of the IR2104 fails and the high-side driver operates for only a few ms. I have substituted 60 V Schottky diodes for the 1N5819s across the MOSFETS. Has this problem occurred before?