Keithley 7038, Instruction Manual

Servicing

4-8

4.5

Troubleshooting

4.5.1 Troubleshooting equipment

Table 4-3 summarizes recommended equipment for trouble-
shooting the Model 7038.

4.5.2 Troubleshooting procedure

Table 4-4 summarizes multiplexer card troubleshooting
steps. Refer to the schematic diagram and component layout
drawing at the end of Section 5 for component locations. 

CAUTION

Use care when removing relays from the
PC board to avoid pulling traces away
from the circuit board. Before attempt-
ing to remove a relay, use an appropri-
ate desoldering tool to clear each
mounting hole completely free of solder.
Each relay pin must be free to move in
its mounting hole before removal. Also,
make certain that no burrs are present
on the ends of the relay pins.

Table 4-3

Recommended troubleshooting equipment

Description

Manufacturer 
and Model

Application

Multimeter

Keithley 2000

DCV checks

Oscilloscope TEK 2243

View logic waveforms

Once the relay control byte has been shifted into the card, the
STR line is set high to latch the relay information into the Q
outputs of the relay drivers, and the appropriate relays are en-
ergized (assuming the driver outputs are enabled, as dis-
cussed below). Note that a relay driver output goes low to
energize the corresponding relay. Channels 1, 5, 9 are select-
ed by deenergizing the relay coils. Q100-105 perform this
function.

The output enable (OE) lines of U101, U102, and U103 are
controlled by the power-up/power-down safeguard circuit
located in the mainframe. This circuit assures that no card
relays are inadvertently energized when the mainframe
power is turned on or off.

Steering and clamping circuits are also included on the driver
outputs. Each driver IC includes two transistors and four di-
odes to perform these functions.

4.4.3 Switching circuits

Signal switching is performed by relays K101 through K109.
K106 through K108 switch channels 1 through 4, K103
through K105 switch channels 5 through 8, and K100
through K102 switch channels 9 through 12.

4.4.4 Card configuration memory

Card configuration information is stored in U100. This infor-
mation is serially read by the mainframe during power-up
and allows the unit to determine the card model number and
card relay configuration information so that the mainframe
can control the appropriate relays accordingly.

Table 4-4

Troubleshooting procedure

Step Item/component

Required condition Comments

1

Digital common
P2001, pin 3 & 16

All voltages referenced to digital common.

2

P2001, pin 2

+6V

Card +6V relay supply voltage.

3

P2001, pin 14

+5V

Card +5V logic supply.

4

U101, U102, U103, pin 2

CLK pulses

During relay update sequence only.

5

U101, U102, U103, pin 3

DATA pulses

During relay update sequence only.

6

U101, U102, U103, pin 7

STR pulses

During relay update sequence only.

7

U101, U102, U103, pins 15–17

Low with relay on,
hi with relay off.

Relay driver outputs.