# Caesar chorus problem



## TheGuy1437 (Jul 20, 2021)

Hey guys, so I fitted all my components on the board and connected everything but I'm still getting no output on the right side of the blend knob so no output at all from the effect. The bottom LEDs seem to be working fine, the ones next to the switch seem to not light up at all. Any ideas what might be wrong. I have also played around with the trim pot with no results...


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## Feral Feline (Jul 20, 2021)

Post big pics clearly focused and well-lit of both sides of your board...


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## Stickman393 (Jul 20, 2021)

Seconded...but...it may to be difficult to troubleshoot without a schematic.

The Cepheid chorus is going to be very similar...I'll hit up the build doc thread, cause I'm in the middle of a Caesar build as well.


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## TheGuy1437 (Jul 21, 2021)

https://imgur.com/a/701ZCMl


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## Stickman393 (Jul 23, 2021)

Check the orientation of C103: I can't tell for sure, but it looks like it may be backwards.


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## TheGuy1437 (Jul 23, 2021)

Yes you are correct it was backwards! I swapped out the capacitor for a new one with the right polarity. Turned it on but still no sound. Should I check the chips with a multimeter?


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## TheGuy1437 (Jul 23, 2021)

Also when I turned it on the red leds were blinking rapidly for a while


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## Stickman393 (Jul 23, 2021)

Voltages on the ICs would help.  Those LEDS appear to be part of the shape switch for the LFO, which will be tied in with the rate control.  When they're connected by the shape switch it looks like they'll pulse at double the LFO rate...I think.

Does the LFO led pulse as well when you apply power?  I'd recommend looking at the offboard wiring as well, down by the switch. A stray strand can easily create a bridge between two pads.


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## ADAOCE (Jul 23, 2021)

That pot might be shorting out against the components in the board. You should insulate those pots. You can buy plastic caps or use some other method .


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## TheGuy1437 (Jul 25, 2021)

The voltages on the chips are:
IC1:

10V - 0,6sudden jumps88,72V24,18V - 4,5Vkeeps oscillating70V - 2,6V - 3,6 Vsudden jumps30V - 3V - 4Vsudden jumps64,7V40,1mV54,1V - 4,5Vkeeps oscillating
IC2 (is this one bad??)

15,18V88,97V25,21V75,19V35,17V65,19V40,1mV55,18V
IC3

10,1mV88,48V24,16V - 4,21Vkeeps oscillating78,49V35,2V - 5,6Vkeeps oscillating64,13V - 4,17Vkeeps oscillating48,16V58,7V
IC4

18,7V88,16V24,13V - 4,19Vkeeps oscillating72,5V - 3,1Vkeeps oscillating30,1mV68,23V - 8,38Vkeeps oscillating44,19V5300mV - 390mVkeeps oscillating



> That pot might be shorting out against the components in the board. You should insulate those pots. You can buy plastic caps or use some other method


I have placed a rubber pad under that pot so I'm confident it's not touching


> Does the LFO led pulse as well when you apply power? I'd recommend looking at the offboard wiring as well, down by the switch. A stray strand can easily create a bridge between two pads.


Yeah, the led oscillates depending on how I set the rate pot immediately when applying power. The other one turns on when I engage the footswitch.

I'm using just a simple HIOKI 3280-10 multimeter so some of the oscillation readings may not be so accurate.


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## TheGuy1437 (Jul 25, 2021)

Also, the schematic diagram just got released for this pedal!!


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## PJS (Jul 25, 2021)

Looking at your voltages pins 7 and 8 of IC3 do not look right.  I am not sure what they are supposed to be exactly, but they will need to be roughly halfway between 0 and 8.7v for audio to pass well.  

The bias voltage is set by the 50k trimpot.  I would be setting the trimmer to give about 4.5V at C12/R28 junction.  Most BBD chorus instructions seem to be saying about that, so that's what I would go for at least to start.  It will be around halfway on the trimpot travel.

Have you got an audio probe?  Trace through and see where you lose signal.


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## TheGuy1437 (Jul 25, 2021)

Ok so I've got 4,5V in the C12/R28 junction but it's 8,5V in the R27/C12 one??? How is that possible... pin 1 of R27 goes to the ground. Do I have a short somewhere? I don't see any contacts touching. The pins on the TRIM are 8,7V, 4,5V, and 0V so I think it's ok. Don't have an audio probe. Might make one soon tho since this board is giving me a headache.


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## IPv6Freely (Jul 25, 2021)

Did you try turning the trimpot? I got absolutely no sound from mine until I adjusted that...


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## Stickman393 (Jul 25, 2021)

TheGuy1437 said:


> Ok so I've got 4,5V in the C12/R28 junction but it's 8,5V in the R27/C12 one??? How is that possible... pin 1 of R27 goes to the ground. Do I have a short somewhere?



In this case you're measuring two different points on opposite sides of a capacitor.  If I understand correctly, a capacitor will block DC voltage, so everything on the R27 side will "fed" from a different source.

VCC and VREF are on opposite sides of the trimpot, and the trimpot is acting as a voltage divider between those two points.  VCC + VREF should roughly equal input voltage.  A hair less, due to the minute voltage drop across the 1N5857 in the power supply.

If you pull the BBD you should see the R27 side drop to 0.  That may be a good first step.  If not, you likely have a short from 9v to that point somewhere.

Caveat; I'm still a newbie when it comes to analyzing semiconductor circuits, so I could be wrong about something here, and fully welcome the more advanced folks on here to point out any errors...


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## PJS (Jul 26, 2021)

I think that Stickman is correct.  both those locations would usually be biased to about 4 - 4.5v but both would get that bias voltage from different places, and may be slightly different.  It would be interesting to see if the voltage at the output changes if you pull the IC.  You also should do a good visual inspection of the joints around that area to see if there are any shorts.


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## TheGuy1437 (Jul 26, 2021)

After removing the chip I got 0V on those pins so there's probably no short circuit in that area. Could the chip be bad? I will check more of the circuit later today


> Did you try turning the trimpot? I got absolutely no sound from mine until I adjusted that...


Sadly no result... Just some popping noise when I'm turning it a lot to the left.
I would buy new chips but they seem to be sold out everywhere in the EU. I got these in a kit from dasmusikding


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## PJS (Jul 26, 2021)

If you could get a new chip easily I would say try that, but if it is going to be hard then may as well look for something else first just in case. I think the time has come to make an audio probe and trace through the circuit to see where you are losing audio.


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