Preamp Test - Warwick WA600 Service Manual

4. Preamp test

Necessary tools: external power supply (symmetrical ±15V) with current meter (or additional current meter),
oscilloscope, sine wave generator, 6.3mm male jack plug with cable
perly by turning output signal off. And finally turn 10 band equalizer on and check if all sliders are working properly. To do this
you it's recommended to change generator frequency accordingly to the values of each slider (35Hz, 70Hz, 140Hz, 210Hz
and so on...)
9. If you don't see sine wave on the scope, try to use different ribbon cable and/or different backboard. If it helps then you
should exchange ribbon cable or backboard.
10. If you anyway don't see sine wave on the scope, you see the sine which is highly distorted, some of potentiometers or
switches doesn't change output signal or they do but with visible 'glitches' or noise then preamp need to be exchanged.
1. Connect preamp board with backboard
using ribbon cable
2. Connect your external power supply to
backboard. Use pins marked red (GND),
yellow (+15V) and blue (-15V). Connect
current meter if it's necessary.
3. Turn on your power supply. Current value
on each line (-15V, +15V) should be
approximately 150-170mA. Perform this
check without input signal.
4. Turn treble and bass potentiometer to the
middle position (12 o'clock), all toggle
switches to the upper position, gain
potentiometer to the middle, volume to
zero.
5. Connect external signal generator
(suggested setting: sine wave
1kHz/1Vpp) to the input of preamp. Use
for that jack plug and connect it to the
passive input.
6. Connect oscilloscope probe to green pin.
Make sure that oscilloscope ground is
connected with generator ground (GND)
or one of red GND points.
7. Start to increase volume potentiometer
to the maximum value. You should see
clean sine wave on the scope. While
voltage on passive input is 1Vpp, output
voltage should be approximately 4Vpp.
When you switch now to the active
input voltage on the output should drop
to approximately 1.25Vpp.
8. Try treble, bass and gain potentiometers,
if movement of each of them is chan-
ging output signal on the scope. Next
observe if wave is changing while you
turn compressor on and also if compres-
sor potentiometer is working properly.
Next try if mute switch is working pro-