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Edited: Nov 10, 2023

Troubleshooting fresh Sum Mix Pan build

Hi,

I've just finished building my Sum Mix Pan PCB+Panel kit and I have to praise de quality of the PCBs, which is one of the best I have encoutered !

The module works great, except for the left side of the second input channel. The left side is completely ineffective :

An audio input in the second channel is only mixed in the right side of the output, with the PAN POT or with the PAN CV input,
The left panning LED (LED8) of the second channel does not ligth up and does not respond to the panning POT, nor to the panning CV input.

The right side of the second channel is OK and the volume controls of the channel are also OK.

My guess is that an OPAMP is dead, but I could not track down which one.

Any help would be apreciated !

Christian.

11 comments

Kommentare (11)

marc9

Jan 25

Hi Stefan,

I´m hijacking the thread - thinking it fits quite well... I´ve finished building the pusherman kit of mix + pan (pre-soldered smd). Unfortunately there is a weird twist with L+R Sum - the signal-path is twisted. Pan R sends audio out L and viceversa. All leds would indicate correctly though. Find a video attached showing what I´m trying to explain.

Problem 2: CH2 is dead - no output while all LED light up. I reflowed all connections, also swapped OTA4 for another working IC - checked on U15, U18, U8, U9 as mentioned below.

I´m hoping this makes sense to you and you can advice what to do next

Cheers, Marc

marc9

Jan 26

Replying to

Somehow and weirdly swapped , yeah

I got it from Pusherman, correct. SMD presoldered.

st-modular

Jan 30

Replying to

Hi Marc, Ok, let me tell you what happend. When we originally planned to release Sum Mix & Pan, we discovered that I had swapped the output sockets due to an incorrectly oriented header, JOUT. This went unnoticed during testing because, in turn, I had also switched the output cables to my outboard equipment.

Nevertheless, we promptly corrected the control board before the release. Unfortunately, it seems that some faulty control boards accidentally made their way into the sale. This is why the outputs on your circuit board do not match the LEDs. I am currently in contact with Pusherman to clarify this.

There are two relatively simple solutions:

Either you also swap the cables at the output sockets or you re-solder them, which I have tried to illustrate in the PDF file linked below. REVERSED OUT WORKAROUND Sorry for all the trouble. Thanks, Stefan

Edited

marc9

Jan 30

Replying to

Hey Stefan,

thank you so much for sharing and drawing 2 simple solutions. I cut the traces on the controlboard and rewired L + R - there is a through hole on the board for running 2 wires to a convinient solderpoint on the other side of board. M+P is in the rack now, can´t take a pic but happy it´s up and running.

Cheers, Marc

christian

Nov 14, 2023

Hi Stefan,

Thanks for helping me out !

I followed your advices, but the problem was still not solved.

I then decided to troubleshoot the module, by following the traces and injecting audio and modulation signals into channel 2.

I discovered that the modulation input on PIN 3 of OTA 4 was not receiving any PAN modulation signal, which led me to identify LED8 as the source of the problem : it appears that the PAN LEDs are in series with the modulation signals, which is not obvious at all! Probably due to the fact that the OTAs use current and not voltage for the signals.

I replaced the LED, and problem was solved, et voilà ! A dead LED is a first for me!

Looking forward bulding other modules : already bought Shikensa, Clipping cat, Push, Matrico and Dirty Dan.

Thanks again for providing us with these great modules, I whish you the best.

Christian.

st-modular

Nov 10, 2023

Hey Christian, Thank you for assembling Mix & Pan. Your soldering work appears to be well done!

If the left side of channel 2 is experiencing issues, I recommend concentrating on reflowing U15 and OTA4. Additionally, please verify the connections of pins 1, 2, and 3 on U18. If the problem persists, consider reflowing U8 and U9.

Please keep me informed about whether these steps resolve the issue. Cheers,

Stefan