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5. Set VR8 fully counter-clockwise.
6. Adjust the DC OFFSET knob until the meter reads 0 volts DC.
7. Set the meter to the 20 volts AC range and slowly turn VR8
clockwise until the meter reads 5.8 volts AC.
Note: Adjusting the DC offset will affect the VAC readings.
TESTING THE TRIANGLE WAVEFORM
1. Switch the WAVEFORM knob to its triangle wave setting.
2. With the meter set to the 20 volts AC range, you should read about
6.3 volts AC.
TESTING THE SQUARE WAVEFORM
1. Switch the WAVEFORM knob to its square wave setting.
2. Set your meter to the 20 volts AC range, you should now read about 12.5 volts AC.
Turn the unit off and unplug it from the AC outlet.
TROUBLESHOOTING CHART
This chart lists the condition and possible causes of several malfunctions. If a particular part is mentioned as
a possible cause, check that part to see if it was installed correctly. Also, check it and the parts connected to it
for good solder connections.
PROBLEM
No wave form at FREQ
No sine, triangle or low amplitude
Saw wave in sine position
Wave forms clip top or bottom
No CLK wave output or low amplitude
No square wave or low amplitude
(FREQ output)
Outputs wrong frequency
DC offset not working
POSSIBLE CAUSE
1. Check voltage at pins 4 (+12V) and 12 (–12V) of U6.
2. Check for wave forms at pin 2 of U6 and pin 3 of U10.
A. Check R3-4, R7, R13, C18-22, C24, SW2-3, VR5 & VR7.
3. Measure voltage at pins 7 (+12V) and 4 (–12V) of U10.
4. Check R8, R9, R11, R14, R44-48, D16, D17, Q1 and Q2.
1. Check U6 pin 2 for wave form.
A. Check VR8, voltage to IC.
1. R5 wrong value.
1. Measure voltage at pins 7 (+12V) and 4 (–12V).
2. Adjust VR8.
3. Check R7, R9, R11, R14, R44-49, D16-17 and Q2-3.
1. Check pin 11 of U6 for square wave.
A. Check Q2 shorted to ground.
B. Check R10, R12 and Q3.
C. Defective IC.
1. Check pin 11 of U6 for square wave.
A. Check Q2 shorted to ground.
B. Check R3, R49, SW3.
C. Defective IC.
1. Check C18-22, C24, R13, SW2 and VR7.
1. Check voltage on VR6 for +12V and –12V; check R8.
-33-
Trim Pot Adjustment
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