downtown fuzz : signal lost

[eh la bas ma]

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 !

[eh la bas ma]

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

[Rob Strand]

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

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.

[eh la bas ma]

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.

[PRR]

I 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.