Giga-tronics 58542 - GPIB Test Functions; 58542 Channel 2 Troubleshooting

58452 VXIbus Universal Power Meter
5-4 Publication 21555, Rev. E, September 2002
5.4 GPIB Test Functions
If the unit will not calibrate its sensors, there are some test functions available through the GPIB. Using
these functions, it is possible to check out the operation of the different parts of the calibrator system.
1. If the calibrator output power as measured in Chapter4 is within tolerance but the unit will
still not complete a sensor calibration, perform the following test to determine if the calibrator
is operating correctly:
a. Send
DIAG:CAL:SOUR 10 from the controller, followed by DIAG:CAL:ATTEN0.
b. The calibrator output should be +20dBm
± 0.8dB.
c. Send
DIAG:CAL:ATTEN 10.
This will insert the 10dB attenuator into the calibrator output. The power should measure
a decrease of 10dB
± 1dB.
d. Repeat Step b, substituting 20, 30 and 40 successively in the command. The power should
be attenuated by the attenuation level specified in the command
± 1dB. This will verify
the condition of all attenuators.
2. This step verifies the oscillator power control circuits. This is done by setting the power to
higher and lower levels and measuring the results.
a. Send the command
DIAG:CAL:ATTEN 0, followed by DIAG:CAL:SOUR X where X is
-3 to +13. The resulting power output should range between -13dB from the first reading
taken in Step 1.a to at least +21dBm.
b. This checks the calibrator control circuits completely. If the unit still will not calibrate a
sensor, the problem is in the measurement circuits, not the calibrator. Proceed to
Section 5.4.1.
5.4.1 58542 Channel 2 Troubleshooting
If only one channel will calibrate, troubleshoot the circuits associated with the channel that fails. The
separate channels are shown on Sheet 1 (Ch 2) and Sheet 2 (Ch 1) of Schematic DWG 21360. If the
unit will calibrate Channel1 but not Channel2, proceed as follows:
1. If the unit fails to turn on the TRIGGER LED when the sensor is connected, the problem is in
the temperature sensing thermistor circuit which connects to U39-3.
Measure the voltage at U5-12. It should be about 2 or 3volts. If it is above 5 or below 0.3volts,
the thermistor circuit is faulty.
2. Reverse the two sensors to determine if one of them is bad.