SOLVED Another Caesar Chorus "No Effect" Thread

[cryptamp]

My issue seems similar to many others posted here but following their troubleshooting hasn't gotten me working. I built three at the same time and none are working. My V3207/V3102 came from eBay and might be bad but I didn't expect 3 out of 3 to be bad. Pics attached might help.
All units' Rate LEDs flash along with the Rate knob adjustment.
All units pass clean signal in bypass.
All units pass clean signal when engaged and cut out volume reduces when Blend turned all the way up (e.g., no wet signal coming from the circuit).
Voltages are listed below. I've highlighted the voltages that seem out of spec based on other past posts.

TL022CP https://www.taydaelectronics.com/tl022cp-tl022-operational-amplifier-ic.html

IC1	Unit 1	Unit 2	Unit 3
1	4.8	4.4	4.3
2	4.4	4.4	4.4
3	5	4.4	4.3
4	0	0	0
5	4.4	4.4	4.3
6	4.4	4.4	4.4
7	4.6	4.4	4.3
8	8.8	8.8	8.8

RC4558P https://guitarpedalparts.com/products/rc4558p-dual-op-amp

IC2	Unit 1	Unit 2	Unit 3
1	5.2	5.1	4.6
2	5.2	5.1	4.6
3	5.2	5.1	4.6
4	0	0	0
5	5.2	5.1	4.6
6	5.2	5.1	4.6
7	5.2	5.1	4.6
8	9.2	9.2	9.2

Trimpots all worked to adjust the above voltages.

V3207 https://www.ebay.com/ipp/253750581429?transactionId=2932391995015&_trksid=p2047675.l48352

IC3	Unit 1	Unit 2	Unit 3
1	0	0	0
2	4.3	4.3	4.3
3	4.5	7.7 (R24 on this unit is labeled 4k7 but reading 3k6)	3.8
4	8.2	7.7	8.2
5	8.8	8.8	8.8
6	4.3	4.3	4.3
7	4.1	8.6	0.143
8	4.2	8.6	0.143

V3102 https://www.ebay.com/ipp/253750581429?transactionId=2932391995015&_trksid=p2047675.l48352

IC4	Unit 1	Unit 2	Unit 3
1	8.8	8.8	8.8
2	4.3	4.3	4.3
3	0	0	0
4	4.3	4.3	4.3
5	0.170	0.096	0.158
6	8.6	8.3	8.6
7	3	3.9	3
8	8.2	7.7	8.2
Clock Frequency*	60hz	30hz	45hz

* Depth turned down and Rate turned up

I need to do some more work on Unit 2's R24. Does anyone have any idea where to look next? I do have more V3207/V3102 pairs from the same seller I can try. Or I can order some from a different vendor.

 

[steviejr92]

That V3107 and V3102 look a little different than what i have. Maybe the possible source? I got mine from cabintech

UPDATE: so I know its probably impossible to tell (crappy camera) but here’s what mine look like granted I haven’t even tried them in my Caesar chorus yet but I got them from a reputable source nonetheless…

 

[MichaelW]

I'm gonna agree with @steviejr92 here and point out that just because you got 3 sets from Ebay if they are bunk, they'll all be bunk.
@Cabintech has these and they are 100% legit 100% of the time.

 

[K Pedals]

I got some I’ll send you a pair…

 

[cryptamp]

I appreciate the offer. I just ordered four pair from Cabintech. I’ll chase the resistor issue and follow up. Thanks all!

 

[steviejr92]

I appreciate the offer. I just ordered four pair from Cabintech. I’ll chase the resistor issue and follow up. Thanks all!

Awesome! Let us know how it goes!

 

[Bio77]

Did you adjust the bias trim? It's a pretty tight range where it works.

 

[cryptamp]

Did you adjust the bias trim? It's a pretty tight range where it works.

What’s a tight range? I spent some time messing with it and found boundaries above and below which no sound went through. If I tried 20 evenly space positions, might I have overshot it?
Also, close to the clockwise limit of function, I might have heard a little bit of pulsing or warble that changed with the Rate knob. Very very subtle, though and still not there when Blend was all the way up.

 

[Bio77]

By tight range, I mean that it works in a small range of positions on the trim. Your voltage on pin 3 of the 3207 seems high. Since the 3207 runs at 5V, I'd expect the bias to be ~2.5V.

This is based on the CE-2. This circuit is weird in that the trim that sets the bias voltage on the BBD also sets the reference voltage for the op-amps. I'm not sure off hand what you could adjust to lower it. Maybe some one else has an idea.

 

[cryptamp]

I did get these to work by changing the ICs. (Another lesson in buying from reputable sources to begin with.) Thanks Cabintech!

By tight range, I mean that it works in a small range of positions on the trim. Your voltage on pin 3 of the 3207 seems high. Since the 3207 runs at 5V, I'd expect the bias to be ~2.5V.

For future readers, "tight" was maybe 15 degrees (think 30 minutes on a 12-hour analog clock). Also, pin 3 on the 3207 was about 3.8 when it was working. Thanks everyone!

 

[MichaelW]

I did get these to work by changing the ICs. (Another lesson in buying from reputable sources to begin with.) Thanks Cabintech!

For future readers, "tight" was maybe 15 degrees (think 30 minutes on a 12-hour analog clock). Also, pin 3 on the 3207 was about 3.8 when it was working. Thanks everyone!

@cryptamp
Glad to hear you got it working! Yah those BBD chips aren't cheap, but pay once, cry once when it comes to getting them from a good source.
I actually think CabinTech is pretty reasonably prices especially compared to trying to get real NOS chips.

Anyway, you can mark this post as "Solved" by editing your original post and selecting the drop down status badge for "solved". It helps with the hygiene of this forum and helps folks focus on threads where people still need help. Thanks!