HP 3457A Service Manual page 223

8-82. Plug-in Cards ¢
In general, to verify faulty operation or to find a failed component of a plug-in card option requires
probing of various signals on the card. In order to probe the card the following disassembly procedures
should be followed.
1) Remove all power from the card and the instrument.
2) Remove the card from the instrument. (see section 6-15)
3) Remove the instrument's top cover. (see section 6-21)
4) Fold the metal bracket, that connects the instrument to the plug-in card, over the front of the
instrument.
5) Remove the shield from the card. This requires removal of four screws. Once the circuit board is
free from the shield, precautions should be taken to prevent the board and its components from being
exposed to electrostatic discharge (ESD). The circuit board should only be handled by properly
grounded personnel.
6) Slide the circuit board into the plastic guides of the metal bracket with the component side up. Two
connections must be made to the board, one to a plastic connector mounted on the metal bracket and
the other to a five wire clamp connector.
7) Be sure that nothing is connected to the instrument's front terminals or touching the exposed circuit
board. Connect power to the instrument and turn it on.
8-83. 44491A @
If the instrument does not work when the card is installed:
a) Check the +5 volt supply coming into the board at connector P801.
b) Cut jumpers JM807/JM808. If the instrument begins working replace U802. If it does not begin
working replace U801. These shift registers can load down data lines SDS, SDO or SDC 2 which will
prevent the instrument from working.
c) Replace jumpers JM807/JM808.
If the instrument works but the channels are not operating correctly, the following items should be
checked:
1) If another relay beside the desired relay is switching, check the steering diodes (CR808-CR827)
associated with the bad channel. For instance, if when switching K802, K808 also switches, check
CR822 and CR823 to make sure they are not shorted.
2) If a relay has some contacts that work correctly and others that don't, replace the relay. To
determine if the contacts are working, instruct a channel to close and then measure the resistance
from the correct pin of connector P802 to the correct pin of connector P803.
3) If none of the contacts of a relay work, the problem must be isolated to either the drive cir-
cuitry for the relay or the relay itself.
a) Measure the resistance of the relay's coil between pins | and 12. The resistance should be
between 60 and 70 ohms.
3457A Multimeter
8-60