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Service Information
4.3.5 Isolator relays
Row isolator relays are necessary in addition to the cross-
point relays in order to ensure the integrity of signal path-
ways. Path isolator relays include K198-K204. The
necessary isolator relay is closed in addition to the selected
crosspoint to complete the entire pathway. For example, if
crosspoint C10 (Row C, Column 10) is closed, relays K199
and K183 would be energized.
4.4
Troubleshooting
4.4.1 Recommended equipment
Table 4-1 summarizes the recommended equipment for gen-
eral troubleshooting.
Table 4-1
Recommended troubleshooting equipment
Manufacturer
Description
and model
5 ½ digit DMM
Keithley 199
Oscilloscope
TEK 2243
Extender card
Keithley 7070
Table 4-2
Troubleshooting procedure
Step
Test point/component
1
DGND
2
+6V
3
+5V
4
NXTADR
5
CLRADR
6
IDDATA
7
STRB
8
RLDAT
9
CLK
10
OE
11
U101-U113
pins 10-18
4-4
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Application
Measure DC voltages
View logic waveforms
Allow circuit access
Required condition
+6VDC
+5VDC
NEXT ADDR pulses
CLR ADDR pulse
ID data pulses
STROBE pulse
Relay data (128 bits)
CLK pulses
High on power up until first
STROBE sets low.
Low with relay energized,
high with relay de-energized.
4.4.2 Gaining circuit access
In order to gain access to the test points and other circuitry
on the Model 7174A, the card must be plugged into the
Model 7070 Extender Card, which, in turn, must be plugged
into the desired slot of the mainframe. The Model 7070 must
be configured as an extender card by placing the configura-
tion jumper in the EXTEND position. See the documentation
supplied with the Model 7070 for complete details on using
the card.
NOTE
Do not use the Model 7070 for performing
verification tests because its presence will
affect the results.
4.4.3 Troubleshooting procedure
Table 4-2 summarizes the troubleshooting procedure for the
Model 7174A Low Current Matrix Card. Some of the trou-
bleshooting steps refer to the ID data timing diagram shown
in Figure 4-2. Refer to paragraph 4.3 for an overview of oper-
ating principles.
Comments
All voltages referenced to DGND (digital
common)
Relay voltage
Logic voltage
Power up only (Fig. 4-2)
Power up only (Fig. 4-2)
Power up only (Fig. 4-2)
End of relay data sequence
Present when updating relays
Present during relay data or ID data (Fig. 4-2)
Power on safe guard
Relay driver outputs
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