Keithley 2001, Руководство по ремонту

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Troubleshooting
2-26
Triggers tests
Triggers are controlled by the 5064 ASIC (U618). This component has seven trigger out-
puts (STO1-STO7) and eight trigger inputs (STI1-STI8). Lines STI1-STI6 and STO1-
STO6 are used to control the system trigger bus, line STO7 is used for Meter Complete,
and line STI7 is used for External Trigger. STI8 is connected to the Group Execute Trig-
ger signal (GET) of the 9914 IEEE-488 bus controller (U622).
Test 105.1 through 105.6 – System trigger bus
Pass/Fail
Defective system trigger bus.
System trigger inputs are normally pulled up to 5V through the protection diodes and
5.1k
Ω
resistors (CR611-CR616, R648-R650 and R655-R657). The Model 2001 can gener-
ate a trigger on any of the six trigger bus inputs by turning on the appropriate FET
(Q602-Q607). These FETs are controlled by system trigger outputs (STO1-STO6) of the
5064 ASIC (U618).
In test 105.1, STI1 is set up as the trigger input. The trigger 1 FET (Q606) is then turned
on and off through STO1, and it is veriÞed that this trips the trigger circuitry in the
ASIC. This test is then repeated for trigger 2 through 6 for tests 105.2 through 105.6.
Success indicates proper operation of the trigger bus.
ASIC, FETs, diodes and 5.1k
Ω
resistors.
Test 105.7 – External Trigger/Meter Complete
Pass/Fail
Short between External Trigger and Meter Complete
This test is similar to System Trigger tests 105.1 through 105.6 except that there is no
internal connection between External Trigger and Meter Complete. Consequently, the
meaning of a failure is reversed from that of the previous trigger tests. A failure is reg-
istered if a trigger does occur. A failure indicates that a short exists between External
Trigger and Meter Complete.
An alternate way to test these triggers is to externally connect a BNC cable from Exter-
nal Trigger to Meter Complete. When test 105.7 is run, the short should cause the test
to fail. If it does not, a problem in the signal path exists.
Type
Failure analysis
Description
High suspect
components
Type
Failure analysis
Description