Technical data

Service and Maintenance 8
Troubleshooting Hints
E364xA User’s and Service Guide 185
Bias supplies problems
Check that the input to the voltage regulators of the bias
supplies is at least 1 V greater than their output. Circuit
failures can cause heavy loads of the bias supplies which
may pull down the regulator output voltages. Check the
voltages of the bias supplies as shown in Table 8- 1 and
Table 8- 2.
Some circuits produce their own local bias supplies from the
main bias supplies. Check that these local bias supplies are
active. In particular, the analog- to- digital converter (ADC),
AC input, and front panel sections have local bias supplies.
Always check that the power supplies are free of AC
oscillations using an oscilloscope. Failure of bias supplies
will cause many self- test failures.
Table 8 - 1 Bias supplies voltages
Bias supply Minimum Maximum Check at
+5 V floating +4.75 V +5.25 V U14 pin 2
–5.1 V floating –4.75 V –5.25 V Anode of CR15
+15 V floating +14.25 V +15.75 V Anode of CR139
–15 V floating –14.25 V –15.75 V Cathode of CR140
Table 8 - 2 Bias supplies voltages (serial MY53xx6xxx)
Bias supply Minimum Maximum Check at
+3.3 V floating +3.135 V +3.465 V U23 pin 3
+15 V floating +14.25 V +15.75 V Anode of CR139
–15 V floating –14.25 V –15.75 V Cathode of CR140