SOLVED Caesar Chorus Stopped Working

[markuus]

I have a Caesar chorus I put together several months ago. To my relief, it worked first try and this has been my favorite build so far- I love how this circuit sounds. However, it crapped out on me recently. First the effect got noisy, distorted, and weak, and then stopped working entirely. I don't get any signal when effect is switched on, regardless of any of the settings. No clean signal comes through when I turn down blend setting. The LFO LED continues to blink and reacts normally to the rate knob. It still passes signal on bypass.

I sort of reflexively assumed it might be an issue with the BBD chips, and ordered some more. Swapping them out didn't change anything. I also tried swapping out the other ICs, also to no avail.

I took voltage readings on all the ICs with all knobs set around noon and switch set to sine wave. I compared to the voltages from this thread, and it seems similar.

SOLVED - Caesar Chorus: No signal or effect

Hey folks! Another one to debug. This time, a Caesar Chorus build. Not getting any signal when Blend is on full. When turned fully counter-clockwise, I get a very low signal. No effect at all regardless of settings. Here's a breakdown of the build. Instead of the V3102D and V3207D IC's, I used...

forum.pedalpcb.com

Any suggestions on next steps? Wondering if I should check anything else before I take it apart and start reflowing various solder joints. Seems like maybe the circuit is working, but signal isn't making it to the output maybe?


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Voltage measurements:

IC1 TL022
Pin 1: Fluctuates
Pin 2: 4.5v
Pin 3: Fluctuates
Pin 4: 0v
Pin 5: 4.5v
Pin 6: 4.5v
Pin 7: Fluctuates
Pin 8: 9v

IC2 RC4558
Pin 1: 4.6v
Pin 2: 4.6v
Pin 3: 4.6v
Pin 4: 0v
Pin 5: 4.6v
Pin 6: 4.6v
Pin 7: 4.6v
Pin 8: 9v
(readings on 1, 2, 3, 5, 6, 7 vary based on bias trim pot)

IC3 V3207D
Pin 1: 0v
Pin 2: 4.3v
Pin 3: 3.9v
Pin 4: 8.4v
Pin 5: 9v
Pin 6: 4.4v
Pin 7: 5.7v
Pin 8: 5.7v

IC4 V3102D
Pin 1: 9,0v
Pin 2: 4.4v
Pin 3: 0v
Pin 4: 4.4v
Pin 5: 0.3v (varies between ~0.1 and ~0.8 depending on setting)
Pin 6: 8.7v
Pin 7: 2.7v
Pin 8: 8.4v

 

[Bobbyd67]

Have you checked if the signal is grounded when switched on ? Might be a foot switch issue

 

[markuus]

@Bobbyd67 how should I go about checking that? Would certainly love this to be a switch issue

 

[Bio77]

Have you checked if the signal is grounded when switched on ? Might be a foot switch issue

Footswitch was my first thought, too.

 

[Bio77]

@Bobbyd67 how should I go about checking that? Would certainly love this to be a switch issue

Check continuity of the lugs in both positions. The 3PDT is basically 3 vertically aligned SPDTs. In my experience you usually lose one of the SPDTs and the other two might still work.

 

[Bio77]

Second guess would be a loose 5088

 

[zgrav]

if those do not give you a solution, use an audio probe to check the path of the dry signal through the circuit to see where it gets lost.

 

[markuus]

Second guess would be a loose 5088

And there it is! The 5088s all seemed fine in their sockets and I had pressed on each one to check it was snug, but the legs on Q1 were a tiny bit wonky and I just swapped it out for a fresh one and pedal is working again! The footswitch is fine it seems- there was continuity as expected in both positions. Not sure if the 5088 itself was bad or just not snug in the socket.

Thanks for that. And thanks for posting IC pin voltages on the other thread- super helpful.

 

[Bio77]

And there it is! The 5088s all seemed fine in their sockets and I had pressed on each one to check it was snug, but the legs on Q1 were a tiny bit wonky and I just swapped it out for a fresh one and pedal is working again! The footswitch is fine it seems- there was continuity as expected in both positions. Not sure if the 5088 itself was bad or just not snug in the socket.

Thanks for that. And thanks for posting IC pin voltages on the other thread- super helpful.

Awesome! General rule of thumb, once the circuit is working, if it stops working it's something mechanical (like a switch or something came loose from moving the pedal and stomping on it.

I'm not a fan of socketing transistors but I know a lot of people do. I'd bet your original 5088 is fine. The socket on Q1 is probably not holding tightly. You can carefully add a bit of solder to one of the legs right where it meets the socket to keep it from slipping in the future.

 

[zgrav]

you can also add a small bit of solder to each leg of a transistor when it is not socketed to make it fit a bit tighter in the socket.

 

[markuus]

@Bio77 @zgrav Good tips! I've gone back and forth on sockets for transistors. Never had an issue either way until now. Maybe I'll switch back to soldering them directly....

Tried again and the original 5088 does in fact work, but I need to press it in the socket in a specific way. Won't stay secure, so maybe socket isn't holding it super well. New transistor seems secure for the moment. If it comes up again I'll know the culprit I guess.

 

[Bobbyd67]

@Bobbyd67 how should I go about checking that? Would certainly love this to be a switch issue

Nice ! You found you're issue^^
To check if a foot switch is faulty just click it on and use a multimeter to check if the input or output is grounded. Put one lead in the screw hole of the enclosure and the other one on the lugs and jacks of your in and out.

Sometimes the inside of the switch can melt when soldering the wires on it and cause all kinds of shenanigans