No sound from Marshall Guvnor clone

[MiguelDamas]

Hi all.

I recently built this kit from Musikding:

https://www.musikding.de/docs/musikding/guvernor/guvernor_schalt.pdf
https://www.musikding.de/docs/musikding/guvernor/govwire.pdf

It passes signal when off. When switched on the LED lights up but no sound goes through. I was wondering if you guys could give me some pointers in terms of troubleshooting the root cause of the problem.

Here are the voltage measurements I took:

R1 - 2.29 / 4.54
R2 through R10 - 0 / 0
R11 - 4.54 / 9.32
R12 - 4.54 / 0
R13 - 1.83 / 9.32
R14 - 0 / 0


C1 - 0 / 2.29
C2 through C12 - 0 / 0
C13 - pos 9.32 / neg 0
C14 - pos 4.54 / neg 0

D1 through D4 - 0 /0


IC:
P1   0
P2   0
P3   4.54
P4   0
P5   2.29
P6   0
P7   0
P8   9.32

board connections:
9v in reads 9.32
LED+    reads 1.83
all grounds read 0


I wired it as per the second link with the exception of the battery clip which I ommited. The power supply is working fine and powers my other builds without any issues. I can solder the battery clip back on if that helps and can also provide pictures if necessary.

Thank you in advance.

[antonis]

Something happens through R1 or your DMM has about 1M input impedance..(Strong coffee should be the No1 tool for troubleshooting.. )
(you should measure +4.5V on pin 5..)

[MiguelDamas]

Thanks for your reply.

I'm a beginner so please bear with me. What do you suggest doing in that case? R1 is measuring at 1M Ohm as per the schematic. Should I replace it?

[antonis]

I supposed C1 short so nominal +4.5V on pin was divided by R1/R14 resistive divider but in case you actually measure R1 value 1M and +2.39V voltage difference across C1 the above doesn't stand..

Considering IC1 RIGHT socket placement (veeeeery common issue.. ) leaves us the choice of faulty RC4558..
(2.25 voltage drop across R1 means than 2.25μA flow inside IC1 via pin 5 - IMHO, too much input bias current even for a BJT Op-Amp..)
The above could only stand in case of measuremets taken WITH IC in socket, of course..

Check first for proper IC1 orientation, 'cause all other measurements (except IC pins) seem to be OK..
(excluding "R2 through R10" which I can't get it's purpose..)

[MiguelDamas]

The IC is definitely oriented correctly.

I measured voltage across all components just in case - what I meant is that R2, R3, ... , R10 all show 0v.

I'm going to grab a couple of new RC4558 and test.

Thank you.

[MiguelDamas]

You were right! I threw in a TL076 and the thing has come to life.

Any ideas on how I may have fried the other one?

I will nip down to the electronics store later to grab an RC4558. Do you have any suggestions of other ICs I can try for different sounds? Or does it not matter all that much?

Thanks again.

[antonis]

Can't guess any obvious cause for damaging RC4558 other than wrong orientation flip while circuit was powered..
(although those ICs are immune to such "cruelties"..)

It can be safely substiduted by any "old-fashion" BJT dual op-amp, like LM1458/1558, LM158/258/358/2904 e.t.c.
Different sound might be obtained by any "ordinary" JFET dual op-amp, like TL072/082/092, LF353/412/442 e.t.c.