Circuit Boardremoval - Keithley 194 Instruction Manual

MAINTENANCE
7.7.2 Circuit Board Removal and Replacement
Removal and replacement of the various circuit boards is
covered below. The circuit boards should be removed in
the order shown, and replaced in reverse order. General
circuit board configuration is shown in Figure 7-8, and cable
connections are shown in Figure 7-Y.
Removal
1. Remove the CARD 2 module (if installed), as follows:
A. Disconnect the two power supply cables and ground
cables.
B. Disconnect the ribbon cable at the mother board end.
C. Remove the two screws that secure the module to the
rear panel.
D. Pull the board free of each plastic standoff (2 for the
1941, 4 for the 1944) by squeezing the standoff slightly
with a pair of pliers.
E. Slide the module back away from the rear panel and
remove it once clear.
2. The I/O board can be removed as follows:
A. Disconnect the channel 1 A/D module power sup-
ply and ribbon cables from the mother board.
B. Remove the two screws that secure the I/O board to
the rear panel.
C. Pull the board partially free of the mother board, but
do not attempt to remove it completely at this time.
D. Disconnect the two ribbon cables going to the display
board attached to the front panel.
E. Remove the two screws that secure the fan control
module to the I/O board and remove the control
module. Carefully lay it aside on the mother board.
F. The I/O board may now be completely removed from
the instrument.
3. Remove the channel 1 A/D module with the procedure
below.
A. If you have not already done so, disconnect the
power supply, ribbon cables, and ground cables from
the mother board. Also, remove the Ii0 board.
B. Turn the instrument upside down and remove the
six screws that hold the A/D module to the three bot-
tom rails (two screws in each rail).
C. Place the instrument right side up, and remove the
two screws that secure the A/D module to the rear
panel.
D. Slide the module toward the front of the instrument
slightly until the connectors clear the slot in the rear
panel, then remove the A/D module completely.
E. If necessary, the input amplifier shield can be re-
moved by removing the three screws that secure it
to the A/D module and the" lifting the shield free
of the board.
4. The mother board may now be removed as follows:
A. Disconnect the wires running to the po\\w switch
and AC receptacle on the rear panel.
B. Disconnect the fan control module and the C1.K BI\'C
jacks from the mother board.
C. Remove the two nuts that secure' the IETE-48X cow
nectar to the rear panel.
D. Remove the four screws that hold the war pdncl to
the sides of the case.
E. Carefully remow the rear panel; the fan co,ntrol
module is loose, so bc sure not to strai" thr ivircs
going from the module to the fan.
E Turn the instrument upside down and rcmovc the
five screws that hold the mother board to the' case
botto"l rails. It will be "ccessary to hold the ho.ud
in place while removing the scre\vs. Thr two end rdijs
have two screws each, while the middle rrlil has ow
ly one screw.
G. Turn the instrument right side up .~nd rcmow the
mother board from the case.
Circuit Board Installation
In general, circuit boards can be installed by r<vcrsing the
above pmcedurc. However, the follo\\jing points should be
noted when installing boards:
1. Make sure that all screws arc properly installed and th'lt
none of the boards is sag&g, possibly causing a short.
2. Make sure that all connectors are properI>; repixed. Ust,
the cable diagram in Figure 7-Y as a fiolde.
3. Pay particular attention to the installation of ribbon
cables. It is possible to improperly position these cables
so that the con"ector is one or more pi"s ofi.
4. Make certain the the A/D, scanner, and Ii0 boards are
properly secured to the rear panel with the screws that
were removed during disassembly.
5. Check to see that the fan control module is properly
attached to the 110 board, and that the I!0 board is tx"-
perly seated in its connector sock&
7-1517-16