HP 8560A Service Manual page 263

8. If the voltage changes incorrectly, proceed as follows:
a. Check the -10 Vdc reference (A3U409 pin 4).
b. While using the front-panel knob to adjust the video trigger level, check for the presence
of pulses on A3U409 pin 15 (LDAC2).
c. While using the front-panel knob to adjust the video trigger level, check for the presence
of pulses on A3U409 pin 16 (LWRCLK).
d. Check that pulses are present on U409 pin 6 (IAO).
9. If the LWRCLK and LDAC2 signals are not correct, refer to "Interface Strobe Select" in
this chapter.
7-10 ADC/lnterface Section