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B) Power Supply Test
Verify that +15V and –15V supplies are at the correct levels.
1) If the LED doesn't light: Check for shorts from +15V to ground, –15V to ground, and
+15V to –15V. Check for opens on +15V and –15V lines. Verify that D204 - D207 are
not shorted.
C) "Mic" LED Test
Verify that "Mic" LED, D202, Lights.
1) If the voltage across D202 is greater than 3V, replace open LED, D202.
Line Amp level for 1V P/P at XLR input connector. Adjust volume control, P201, fully
clockwise.
D) Gain Test
1) Place S201 in "Line" mode (switch out), Turn on generator A, set frequency to 400Hz
and adjust.
2) Verify that voltage at output, pin 1 of J204 = 800mV P/P (+/– 100mV)
3) Verify presence of 400mV P/P (+/– 50mV) at pin 1 of U202.
4) Remove oscillator connection to XLR input. Verify resistance from pin 2 of J202 to pin 2
of U202 = Pin 3 of J202 to pin 3 of U202 = 24.75K. If not, check for shorted sections of
S201. Verify resistance from pin 2 to pin 1 of U202 = pin 3 of U202 to ground = 10K. If not
check for opens and shorts around U202.
5) Rotate Volume control counter clockwise while monitoring pin 1 of P204. Voltage should
gradually decrease to zero. If the level is intermittent or control does not attenuate, replace
defective P201.
E) Line Amp Frequency Response Test
Advance volume fully clockwise and adjust for 800mV P/P at pin 1 of J204. Change Fre-
quency to 20kHz and verify a level of 750mV (+/– 100mV). Change frequency to 20Hz and
verify a level of 750mV (+/– 100mV).
F) Line Amp Common Mode Rejection Test
Set generator output drive to unbalanced. Adjust frequency to 400Hz. Bring volume
control fully clockwise and adjust oscillator output to obtain 10V P/P at pin 1 of J204. Lift
pin on R227 that is closest to J201 and solder it to pin on R226 that is closest to J201.
Reapply power to board and verify that the voltage present at pin 1 on J204 is less that
250mV P/P. Readjust frequency to 20kHz and verify that the voltage present at pin 1 on
J204 is less that 250mV P/P.
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