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Input Assembly Trouble-shooting
A) Initial Setup
Connect board under test to a +/– 15V power supply according to the following pin out:
pin 3 = +15V, Pin 4 = –15V and pins 2 and 5 = power ground. Connect a function
generator output to XLR input connector.
B) "Mic" LED Test
Turn Generator A off. Place Mic/Line switch, SW1 in "Mic" position, power up board and
verify that "Mic" LED, D6, lights. If the voltage across D6 is greater tan 3V, replace LED.
If LED doesn't light check power supply (see "C" below) and check IC #6 (power rail pins,
pin 3 = +15V, pin 12 = –15V) and check for any shorts or open traces around the IC.
C) Power Supply Test
Verify that +15V and –15V supplies are at the correct levels.
Check for shorts from +15V to ground, –15V to ground and +15V to –15V. Verify that
D1- D4 are not shorted.
D) Line Gain Test
1) Mic Input Gain: Place Mic/Line switch. SW1, in "Line" mode (switch out), set generator
level at 0.5V at 1kHz into XLR input connector J10, channel 1. Do not plug anything to the
Patch nor to the Phone Jacks. Adjust volume control, R47 (Master) and R48 (Channel 1),
fully clockwise, and all EQ controls flat (at center detented point).
• Verify that the voltage at pin 1 of J1 is = 1.28V (+/– 100mV).
• Verify 215mV (+/– 50mV) on pin 1 of U1A and pin 1 of U3A (Meter Feed).
• Verify 430mV (+/– 50mV) on pin 7 of U1B.
• Verify 0.5V on pin 1 and 7 of U7, pin 1 and 7 of U8.
• Verify 400mV (+/– 25mV) on pin 1 of U4A. If voltage is low inspect Effects Patch
input output jack and traces/solder around it.
• Verify 1.28mV (+/– 100mV) on pin 7 of U4B.
2) Channel 2 Gain: Since channels 2 and 3 are electronically identical, we will discuss
channel 2 only. Please refer to schematic for channel 3. Make sure that nothing is plugged
into Patch and Phone Jacks. Set generator level at 0.5V, 1kHz, at 1/4' input jack connector
J5, channel 2. Adjust volume controls, R47 (Master), and R49 (Channel 2 Volume), fully
clockwise. Set all EQ controls to flat (at center detented point).
• Verify 0.5mV (+/– 25mV) on pin 1 of U2a (U2B).
• Verify 0.5V (+/– 25mV) on pin 2 of R49 that is located on the control board.
• Verify that there is 0.5V (+/– 25mV) on pin 1 and 7 of U7, and pin 1 and 7 of U8.
EON 15PAK
47
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