Service manual

Troubleshooting 37
YES
NO
NO
NO
NO
YES
YES
YES
START
"DAC DEFECTIVE"
TURN OFF SUPPLY AND REMOVE TOP COVER.
TURN ON SUPPLY AND CHECK BIAS AND
REFERENCE VOLTAGES (TEST POINTS 9
THOUGH 22 . (SEE TABLE 6-3*).
* IF THE SUPPLY FAILS SELF TEST, TURN OFF
THE SUPPLY, DEPRESS THE 7 KEY AND THEN
SO AS TO SKIP SELF TEST.
ARE
VOLTAGES
OK?
PROBABLE DEFECTIVE A6 BOARD
SHORT A10U506-1 (SA MODE) TO A10U506-20 (COM),
SEE FIG. 3-15. TURN ON SUPPLY AND WAIT TWO
SECONDS THEN REMOVE SHORT. WAIT FOR "POWER
ON INIT" TO COMPLETE. USE A SCOPE TO CHECK
THE CV DAC (A10U513-6), CC DAC (A10U514-6) AND
READBACK DAC (A10U515-6) OUTPUTS. COMPARE
THE WAVEFORMS GIVEN IN FIG 6-1.
IS ONE
DAC MISSING
STEPS?
ARE ALL
DACS MISSING
STEPS?
IS
CV OR CC DAC
DEFECTIVE?
NO
YES
CHECK REF VOLTAGE FOR CV/CC DACS AT
A10U504-6 37 WITH RESPECT TO 36 .
DOES A10U504-6
= 10V?
THE WAVEFORMS TAKEN AT THESE POINTS WITH
TURN IT ON WHILE HOLDING THE KEY DOWN
PROBABLE DEFECTIVE A10 BOARD
PROBABLE DEFECTIVE A10 BOARD
PROBABLE DEFECTIVE A10 BOARD
PROBABLE DEFECTIVE A10 BOARD
PROBABLE DEFECTIVE A10 BOARD
Figure 3-7. DAC Circuits Troubleshooting)