SOLVED Knight of Tone (KOT) from PCB Guitar Mania

[ntuncer]

Hello all,

After 2 days of trying to find the problem, I have nothing, I am desperate and really need your help. This is a PCB Guitar Mania's Kot which there is a 18v charge pump. Both switches work fine with leds, there is a sound in bypass but there is no sound when I engaged, both channels have same problems.

Result of my diagnostic:

• I used audio probe and find that there is a sound on IC1's pin 3 and not pin 3. And checked the other pins. I found that I have voltage problem.
  • When I remove IC's and read the voltage:
    Pin 4 = 0 v as expected
    Pin 5 = 0 v it suppose to be around 9v as Vb
    Pin 8 = 0 v it suppose to be around 18v
• When I check the power section I have 17.39v from output of D15
• If I remove R13's one leg I have 17.39v in Pin 8 of IC1
• I have already replaced almost everything on pover section, R12, R13 and C10 but result is same.
• When I check the continuity from Pin 5 and 8 to ground, they seem fine nothing to the ground.
• I have already replaced IC3 but the result is same

I am totally blocked and I have nothing to try anymore. Could you please help me to find the issue please? I have already build lots of same pedal but on this one my skills are not enough to go further.

Here is the schematic:



Photos inside:





Cheers

 

[ntuncer]

So I measured all the voltage values on the schematic all Vcc and Vb values are correct. I replaced the IC1 and IC2 with Rc4558 in case of I burned them. I repass the solders everywhere. Now pcb is out of the box. When pedal is in bypass there is a background sound and when I activate the fx there is a high pitch noise in both channels. What should I do next to search the issue?

a Working pedal IC1 Voltage values (left) vs non working pedal's IC1 values:
1: 8.45 8.68
2: 8.46 8.68
3: 7.68 7.88
4: 0 0
5: 8.37 8.50
6: 8.38 8.52
7: 8.35 8.50
8: 16.76 17

By the way for C10's + leg with the working pedal I can read 8.18v but For non working I can only read 1.45v .

 

[giovanni]

Did you replace the melted caps?

 

[ntuncer]

Did you replace the melted caps?

I tried to say burned means they become faulty. For C10 I bridge it with a cable to R12 cause the pad on pcb was defected. Now there is no pitch noise. I checked the first channel it seems working fine. I will check other one and if it is ok I will box it again to test.

 

[ntuncer]

Finally boxed it and everything works perfectly. Thank you very much @giovanni ! Without you I cannot make it and already gave up. I learned a lot from you. Let me know if you visit Paris. Beers on me!

Cheers

 

[giovanni]

That’s great! Glad I could help! I’ll let you know the next time I’m in Paris (I’m from Italy but live in nyc so it may happen…).