6-10 Service Guide
Digital Control Troubleshooting 8719ET/20ET/22ET
Troubleshooting the GSP (A19) and the Display (A18) 8719ES/20ES/22ES
RF Network Analyzers
Run Display Test 55
1. Press the following:
• If the analyzer passes the test, it will display 55 DISP/CPU COM PASS. Press
and go to “Run Display Tests 59-61” on page 6-12.
• If the analyzer fails the test, the display will appear blank and the front panel LEDs
will stay on. Continue with the next check.
Inspect Ribbon Cable Repeat Display Test 55
Inspect the ribbon cable (W20) that connects the CPU board (A7) to the GSP (A19) for a
loose connection. Repeat “Run Display Test 55.” If the analyzer fails the test, a walking one
pattern will be continuously transferred from the CPU, through the cable, to the GSP.
Immediately go to the next check.
Perform Walking One Pattern
Use an oscilloscope and a probe to verify that a walking one pattern is transferring from
the CPU board (A7). The walking one pattern similar to the one shown in Figure 6-6 and is
found on pins 3 through 10, and 13 through 20. (See Figure 6-5.)
• If the signal is present at the A7 connector of the ribbon cable, verify that it is present
at the other end of the cable.
• If the signal is not present, replace the cable.
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