K2 - ERROR 405.2 – Absolute value x10 gain comparison; large +DAC output
Voltage at A/D IN not the same as test 405.1.
DAC U531 is programmed to generate . That signal is then applied to ACF through R560 and U532 (DAC line pulled low). ACF is routed to AMP IN via U526, Q516, and the AC input buffer.
AMP IN is tied to the inverting and non-inverting paths of the variable gain amplifier (VGA). NETOUT (output of U519) is routed to the Zero-Crossing Amplifier which, based on the polarity, generates the appropriate COMP- signal that is applied to com- parator U507. The comparator selects the path that the AMP IN signal will follow through the VGA by closing the appropriate analog switches of U509.
The positive (non-inverting) AMP IN signal path with the VGA at x10 is through R530, Q508, Q507, U519, R531, U509, Q501, and U516 to pin 12 of multiplexer U511. The out- put (OUT) of the multiplexer is routed through buffer U342 to ACV/A. The signal at ACV/A is routed through U320 (/AC pulled low) and applied to the A/D buffer (U322), which is configured for x1 gain.
Measure the voltage at A/D IN. It should be same value that was measured in test 405.1.