The Contortionist II Troubleshooting Supplement
After thoroughly double-checking your connections, the next step is to take DC voltage measurements to help locate problem areas.
TONE
100KA
FUZZ
Using a volt meter, connect the ground side lead of the meter to any ground point on the pedal. One ground point would be the input or output jack’s sleeve lug. The other volt meter lead will be used to measure DC voltage at the test points listed here.
5
1
1
17
3
18
I
15
14
MPS
A13
E
1
E
D
F
2
3M
4
331K
G
B
C
B
H
10
11
Q2
10K
6
9
E
10K
7
C
1
4
7
2
5
8
3
6
SLEEVE
8
180
9
BLK
SLEEVE
0.8 VDC
4.3 VDC
4.6 VDC
3.9 VDC
I (Q3 Emitter)
3
.1µ
Q1
2
RED
4
µ
3
1
1.8 VDC
H (Q2 Emitter)
1
C C
B
820K 12
13
A
1.9 VDC
G (Q2/Q3 Base)
7
19
2N
3906
E
RING
F (Q2/Q3 Collector)
.22
Q3
.1µ
E (Q1 Emitter)
.0039µ
1.5K
2N
3904
16
2.7 VDC
D (Q1 Base)
B
2
9.1 VDC
C (Q1 Collector)
3
+
2
10K
B (Indicator LED Anode)
2
-
Measurement
A (Power Supply)
250KA
6
22µF 50V
If you are using only a battery for power, be sure to plug a guitar cable into the input jack when taking measurements. Any major differences from the voltages listed should indicate a problem area.
DC Test Points
VOLUME
1KL
5.2 VDC
TIP
Measuring AC Voltages from the Guitar Signal
TIP
Lettered test points are for DC
Numbered test points are for AC
Once your DC voltages are in order, if your kit is still not working properly, you can measure AC voltages along the signal path to troubleshoot further.
You will need a volt meter that can measure the small signal AC voltages that electric guitars put out. The output signal from your guitar will likely be less than 1 V.
First, measure the output signal directly from your guitar. You can do this by plugging your guitar cable into the guitar and leaving the other end of the cable disconnected. Connect your meter across the disconnected ¼" plug's "tip" and "sleeve" sections. Make sure your guitar's volume and tone controls are turned up and strum a chord. When you strum, you should see the AC voltage reading on the meter quickly rise to some maximum value and then fall back to
0 VAC when you stop strumming and the strings are at rest.
Tip
Terminal
(Output)
Tip
Spring
¼” Jack
¼” (Mono) Plug
Sleeve
Tip
Sleeve
Terminal
(Ground)
Once you are able to measure the output signal from your guitar directly, plug the guitar into the input jack of your kit and use the AC test points to measure the guitar signal along the signal path. Start with test point one and move along in order. You should be looking to identify the last test point where the signal seems normal and the first test point where the signal seems unusual or where it is no longer even present.
·
·
B
+
Lettered test points are for DC
Numbered test points are for AC
180
2.7 5
VDC
6
center (-)
AC Voltages (bottom) measured with 1KL pot set to min gain.
100KA Tone set to Max.
AC voltages measured while strumming an open E chord on a strat with single coil neck pickup
(volume and tone turned all the up).
Foot
Switch
(C) 4
-
AC Voltages (top) measured with 1KL pot set to max gain.
100KA Tone Set to Max.
·
·
DC Power
Jack
DC Voltages measured with respect to ground.
37 mA(DC)
A
9.1 VDC
10K
5.2 VDC
Q3
3
10K
3M
+
9 VDC
Battery -
Input
.1µ 1.8
0.2 VAC
VDC
C
Q1
D
Foot
Switch
(A)
4.6 VDC
B
0.4 VAC
820K
E
I
1.4 VAC
1.9
VDC
2.3 VAC
C
B
.1µ
F
0.7 VAC
2
330p
MPSA13
0.3 VAC
C
B
5
0.8 VAC
.22µ
6
7
1.5K
0.8 VAC
0.3 VAC
100KA
7
TONE
250KA
.0039µ
2N3904
OUTPUT
G
E
Foot
Switch
(B)
Output
8
9
4.6 VDC
1
3
4
C
4.3 VDC
0.2 VAC
0.2 VAC
1
2
2N3906
Q2
E
H
3.9 VDC
E
10K
0.8 VDC
1KL
GAIN
+
22µ
P-H501
MPSA13
NPN Darlington Transistor
3PDT
Footswitch
A
B
C
1
4
7
2
5
2N3904
NPN BJT
Collector
Collector
C
B
MPSA13
Base
Base
8
E
3
2N3906
PNP BJT
6
9
E
B C
E
B C
Emitter
E
B
C
Emitter
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“The Contortionist II” (K-965)
Schematic 