Hello,
I confirm Downtown Fuzz stopped working for some reason. Yesterday it was fine.
https://lectric-fx.com/wp-content/uploads/2019/09/Downtown.pdf
BOM https://drive.google.com/file/d/1LupjSSG5nm0bJQmdsELjdwb2XpmEELHs/view
DC 9v+ = 9.84 V
IC1 : NJM4558
1= 8.87 V 8= 9.84 V
2= 4.41 V 7= -137 mV
3= -9.27 V 6= 5.3 mV
4= -9.27 V 5= 5 mV
IC2= CA3080
1= 0 V 8= 0 V
2= 0 V 7= 9.84 V
3= -1.2 mV 6= 5.3 mV
4= -9.27 V 5= -8.72 V
IC3: LM1458
1= -30 mV 8= 9.84 V
2= 0 V 7= -41.2 mV
3= 0 V 6= -19 mV
4= -9.27 V 5= -18 mV
IC4: NJM4558
1= -7.84 V 8= 9.84 V
2= 3.680 V 7= -98.5 mV
3= 0 V 6= 0 V
4= -9.27 V 5= 0 V
IC5: NJM4558
1= 7.33 V 8= 8.92 V
2= 7.33 V 7= -7.29 V
3= 8.87 V 6= 3.891 V
4= -8.72 V 5= 33.1 mV
IC6: NJM4558
1= -7.27 V 8= 8.92 V
2= 2.712 V 7= 8.22 V
3= 32.2 mV 6= -156 mV
4= -8.72 V 5= 56 mV
IC7: LM1458
1= -3 mV 8= 9.84 V
2= 0 V 7= 15 mV
3= 0 V 6= 1.6 mV
4= -9.28 V 5=0 V
IC8: LM741
1= -9.27 V 8= 0 V
2= 0 V 7= 9.84 V
3= 0 V 6= -6.62 V
4= -9.28 V 5= -9.27 V
IC11: LM311N
1= 0 V 8= 9.83 V
2= 4.76 V 7= 9.84 V
3= 4.76 V 6= 9.44 V
4= 0 V 5= 9.75 V
IC12: LM311N
1= -9.28 V 8= 9.84 V
2= -1.140 V 7= -9.25 V
3= 12.3 mV 6= 9.75 V
4= -9.28 V 5= 9.75 V
IC13: CD4013
1= 8.71 V 14= 9.84 V
2= 8.73 V 13= 8.37 V
3= 9.83 V 12= 8.71 V
4= 8.71 V 11= 8.71 V
5= 8.73 V 10= 8.71 V
6= 8.71 V 9= 8.72 V
7= 8.71 V 8= 8.72 V
IC14: LM13700N
1= -8.05 V 16= -8.05 V
2= 1.2 mV 15= 1.6 mV
3= 0 V 14= 0 V
4= 0 V 13= 0 V
5= -8.12 V 12= -8.11 V
6= -9.28 V 11= 9.84 V
7= 0 V 10= 0 V
8= 2.3 mV 9= 1.2 mV
IC15: LT1054
1= 2.682 V 8= 9.85 V
2= 5.41 V 7= 221.6 mV
3= 0 V 6= 4.97 V
4= -4.13 V 5= 0.707 mV
All transistor pads are fluctuating between -1 mV to 2 or 3 mV. I took Q1 out and same readings on the sockets : near 0 V
What could go wrong with these transistors, why are they all around 0 V ?
Every help is welcome !
I have different readings on IC15 : LT1054, no idea why it changed like that. Still no signal, only in bypass.
IC15: LT1054
1= 1.401 V 8= 9.85 V
2= 5.41 V 7= 1.440 V
3= 0 V 6= 2.566 V
4= -4.13 V 5= -9.28 mV
And i have new readings on transistors :
Q1
E= 0 V
B= 0V
C= -8.71 V
Q2
E= 0V
B= -40 mV
C= -9.26 V
Q3:
E= -8.64 V
B= -8.11 V
C= 9.81 V
Q4, Q8:
G= 8.91 V
S= 8.91 V
D= 8.91 V
Q5:
C= -47.7 mV
B= -8.64 V
C= -9.28 V
Q6:
C= 9.80 V
B= -8.11 V
C= -8.63 V
Q7:
C= 86.9 mV
B= -8.64 V
C= -9.28 V
QuoteIC1 : NJM4558
1= 8.87 V 8= 9.84 V
2= 4.41 V 7= -137 mV
3= -9.27 V 6= 5.3 mV
4= -9.27 V 5= 5 mV
The voltage on IC1 pin1 is wrong, it should be around 0V. It really looks like you have a solder bridge between pin 3 and pin 4.
Because of the DC coupling between IC1 and some of the other ICs the IC1 pin 1 voltage is probably screwing up a lot of stuff.
Ayaaaah !
Thanks Rob ! You found it ! May the diy goddess give precision and reliability to all your ICs !
I reflowed IC1 and cleaned spaces between pads. I took off the IC and read with a DMM on the socket pin 1 : 0 V.
Then i put the IC back and still 8.87 V on pin 1. I replaced the IC with an other one and hurrah ! 0 Volt ! Sub-octave+fuzz is back on...
I guess the RC4558P became defective after two years of good use.
All my thanks ! I am going to play quietly and suddenly push the gain up now.
Quote from: eh la bas ma on September 28, 2022, 10:55:22 AMI guess the RC4558P became defective after two years of good use.
It has no input protection. Strong static shock or plugging to bad places -will- blow that input.
Lift one leg of C1 and add a few K of resistor. This slightly cuts your gain but that is better than unexpected failure.
(https://i.postimg.cc/9rn8yy7T/ellabasma-42.gif) (https://postimg.cc/9rn8yy7T)