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Diagnostic Testing and Troubleshooting (2635A)
Analog Troubleshooting
5A
5A-11
Note
When making voltage measurements in the invertercircuit, remember that
there are two separategrounds. The outguard ground is the ’GND’ testpoint
(A1TP1), and the inguard ground is the’COM’ test point (A1TP30).
The inguard regulator circuits for VDD and VSS have current limits. Shorts and heavy
loads between VDD and COM, VSS and COM, and VDD and VSS will cause one or
both supplies to go into current limit. The current supplied by either supply can be
checked by measuring the voltage across the current sense resistors, A1R13 and A1R15.
The typical voltage across A1R13 is 0.30, and the typical voltage across A1R15 is
0.40V.
Generally, open electrolytic capacitors in the inverter supply will cause excessive ripple
for the affected supply. Also, the rectified dc voltage for the supply with the open
capacitor will be lower than normal. Normal voltage levels at the rectifier outputs for
each inverter supply are shown in Table 5A-2.
The loads for the inguard supplies can be disconnected by removing the cable to the A/D
Converter PCA at A3J10. The inguard regulator circuits and VDDR regulator will
operate with no loads, and troubleshooting can be performed by making voltage
measurements.
The normal input current to the inverter supply is about 11.25 mA, or 0.225 mV across
A1R38 (when the instrument is not measuring).
Table 5A-3 provides a Power Supply troubleshooting guide.
5A-10. Analog Troubleshooting
Warning
To avoid electric shock, disconnect all channelinputs from the
instrument before performing anytroubleshooting operations.
Refer to Figure 5A-4 and Figure 5A-5 for test point locations on the A/D Converter
PCA.
First, check for analog-related errors displayed at power up. An ’Error 9’ means that the
Main Microprocessor A1U1 is not able to communicate with the A/D Microcontroller
A3U9. ’Error A’ and ’Error b’ mean that a failure has occurred in the internal memory of
the A/D Microcontroller A3U9. ’Error C’ means that the Analog Measurement Processor
A3U8 is not functioning properly.
Check the inguard power supplies on the Main PCA with and without the A/D Converter
PCA connected. The inguard supplies must be measured with respect to COM testpoint
A1TP30.
Power Supply Test Location Acceptable Range
VDD
VSS
VDDR
A1TP31
A1TP32
A1C6+
5.00 to 5.70V dc
-5.10 to -5.75V dc
5.30 to 5.95V dc