Fix 401.1 - Signal switching; zero cal switch
Failure: Cannot measure 0V ±0.001V at A/D IN.
Common is routed to the ACF line through U526 (SHORT pulled low). ACF is then
routed through multiplexer U511. The output of the multiplexer (OUT) follows the
same path to the A/D buffer (U322) as the 400 series tests. U322 is conÞgured for x1 gain. Measure 0V at A/D IN.