HP 3457A Service Manual page 225

8-84. 44492A
If the instrument does not work when the card is installed:
a) Check the +5 volt supply coming into the board at connector P851.
b) Cut jumpers JM851/JM852. If the instrument begins working replace U852. If it does not begin
working replace U85I. These shift registers can load down the serial data lines SDS, SDO, or SDC2
which will prevent the instrument from working.
c) Replace jumpers JM851/JM852.
If the instrument works but the channels are not operating correctly, the following items should be
checked:
1) Check for the correct output from U851 and U852. All outputs should be high except for the
output to the relay being closed. To close relay K851 (channel 0) requires that output QI of shift
register U851 be held low. The drive signal must remain low the entire time the relay is closed.
2) If the output of the shift registers is correct, check the output of drive transistors U853-U855,
If relay 851 is closed, the output of U854 pin 14 should be approximately +5 volts. If it is not,
replace the transistor pack.
3) If the drive signal is working and the contacts do not operate correctly, replace the relay.
Contact operation can be checked by making a resistance measurement from the correct pin of
connector P853 to the correct pin of connector P852. To check the high contact of relay K851,
resistance should be measured between connector P853 pin | and connector P852 pin 22.
8-85. Replacement Procedures
Procedures for the removal and replacement of the PC assemblies are contained in Section VI of
this manual. Please observe clean handling techniques and anti-static procedures when handling the
PC assemblies.
3457A Multimeter
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