CUMMINS QST30 - Troubleshooting Analog Signals between Analog and Digital Boards

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Copyright  2017 Cummins Inc.
TABLE 4-30A. TROUBLESHOOTING ANALOG SIGNALS BETWEEN ANALOG AND
DIGITAL BOARDS
WARNING
Many troubleshooting procedures present hazards that can result in severe personal inju-
ry or death. Only qualified service personnel with knowledge of fuels, electricity, and machinery haz-
ards should perform service procedures. Review Important Safety Instructions page.
NOTE: Perform this procedure after you have isolated the problem to either the analog board
(A33) or to the digital board (A32). You must have schematics and wiring diagrams to
identify the various inputs and outputs.
*1. Check that the input to the analog board is correct. There are a few signals (e.g.: 3PH Ave, Line Freq,
Phase Angle 1 to 3, Lead Lag) that are derived from one or more input signals.
1a. To check the sensor input voltages into the analog board, connect the sender simulator and test the
voltage across the + and − inputs at A33 J1 using harness tool. (This assumes that you have verified
that the harness and the engine interface board is good.)
 If the input voltage to the analog board is correct (refer to Table 4-30), go to step 2.
 If the input voltage to the analog board is incorrect, check for 12 VDC at A32 J3-20 and 5 VDC at
A32 J3-12. Do this with the analog board connected to the digital (A32).
If the 12 VDC and 5 VDC voltages are OK, replace the analog board.
If the 12 VDC and 5 VDC voltages are not OK, disconnect A32 J3 and recheck for 12 VDC at
A32 J3-20 and 5 VDC at A32 J3-12.
If the 12 VDC and 5 VDC voltages are now OK, replace the analog board.
If the 12 VDC and 5 VDC voltages are still not OK, replace the digital board.
1b. To check the AC inputs into the analog board, drive the PT/CT inputs (voltage or current) and verify
that the input is correct.
 If the input to the analog board is correct, go to step 2.
 If the input to the analog board is incorrect, disconnect the ribbon cable at A34 J5 and check the volt-
age at A34 J5 again (Customer Interface).
If the voltage is now correct, replace the analog board.
If the voltage is still not correct, the problem is not on the analog or digital boards.
2. If the input to the analog board is correct, determine whether the signal is multiplexed (refer to Table
4-30). If the signal is not multiplexed, go to step 2a. If the signal is multiplexed, go to step 2b.
2a. This step is for non-multiplexed AC signals. Drive the input to the analog board with an AC source,
and test the signal level out of the analog board. You must calculate what the analog output voltage
should be (Table 4-30), assuming the analog board transfer function is linear.
 If the signal level into the digital board is correct, the problem must be on the digital board. Replace
the digital board.
 If the signal level into the digital board is incorrect, remove the ribbon cable connector at A32 J3, and
check the front panel digital display of the bad analog value.
If the display reads 0, replace the analog board.
If the display reads a value other than 0, replace the digital board.
*CAUTION: Wearing a wrist strap, set S12 to Off and A32 S5 to Standby before connecting/disconnecting harness plugs.