K2 - Error 402.1 - Frequency switch
Cannot measure 0.032V ±0.005V at A/D IN.
OUT B of the DAC (U531) is set up to output 4.33V at PRECOMP+ (U528 pin 1). The operation of the frequency switch, U522 (FREQ pulled low), is verified by dividing the PRECOMP+ voltage by the voltage ratio across R560 and R558. The “on” resistance (approximately 25Ω) of the analog switch (U522) is added to the resistance of R558 since it is part of the ratio. Again, as in the 400 series tests, this voltage is routed to the A/D buffer (U322) which is configured for x1 gain. Measure 32mV at A/D IN.
U322 - x1 gain