Cepheid parts selection/general PCB question

[cylnplnt]

I’m preparing to build the Cepheid Chorus attempting to use parts as close to the original as possible. I’m mainly using the article on electrosmash.com as reference. One part has me stumped. What I’m finding in examining old pedals is there absence of box caps. The Cepheid calls for a 1uf box cap in C20. From what I think I can determine this was an Electrolytic in the original(C17 in the boss schematic). My questions are:
-If I wanted to use an Electrolytic how do I determine which direction the polarity is in the Cepheid PCB?
-Is there a general way to tell the direction for polarity on a PCB?

I’m an absolute beginner with an interest in recreating classic pedals. I am only just beginning to understand how to read schematics. The extent of my multimeter knowledge is how to test resistors, and test which direction diodes go. I’m still grappling with technical terms.

 

[mjh36]

Mainly, the best way is using a multimeter to find connectivity. If you find what C20 pad goes to what resisitor, you'll be able to determine which way to install the electrolytic. Sometimes you can see the traces visually, on this example the traces for C20 may be on the other side of the board.

On the Cepheid schematic, C20 is inbetween R40 and R41. If copying the electrolytic example, you can the see the positive+ goes to one side of R40, and the negative- goes to one side of R41. So I would take a multimeter and probe one pad of C20, and see which resistor it goes to. That'll tell you the polarity direction you need to put it in.

Another PCB image off of the Cepheid ordering page shows some connectivity visually of the surrounding components. I was able to more or less show what goes where. You just need to probe where each C20 pad goes, either R40 or R41. Compare this image to the schematic and you can kind of puzzle piece it together.

However, I have no idea of the tonal differences, if any, that would make. Anyone else can chime in on that.

Let me know if you need more help!

 

[cylnplnt]

Ok. I tested for continuity. I got continuity from the right side pad only of R40(470k), to the right hand pad of C20. Continuity from the left pad only of R41(100k), to the left pad of C20. You can also see the traces from these points on the back and front of the board.

Just to clarify I understand. R40 is the positive side due to it coming before C20. And R41 is negative side because it comes after. Current is flowing towards C20 from R40 then onto R41. This dictates the positive side needs to be in the right pad of C20 and the negative in the left. Correct?

 

[cylnplnt]

I also just noticed these small numbers. Does “1” and “2” correspond with the left(1) and right(2) through holes for the components?

 

[mjh36]

Yup looks good to me! You got it exactly right. The fact that you can physically see the traces confirms too. And it'll only be one pad of each resistor like you said, because that is the side to which it directly connects. Look at a couple connection points on the schematic, and try to find and probe the connectivity on the board. Do that a few times and it'll start to click how each component connects to the next. Like the other side of R41 (100k). The only place it connects to is ground. So if you probe those two spots, you'll get the beep, but nowhere else, since that's the only points of connection.

 

[mjh36]

I drew the symbol for the electrolytic above the bipolar cap on the schematic in the image above.

 

[mjh36]

I'm not sure what those little numbers mean. I only pay attention to those if there's more than 2, like an IC chip or something which has 8 legs.

 

[cylnplnt]

@mjh36 Thank you so much for the insight. I feel like this took my general understanding to another level.

 

[mjh36]

You got it dude! Happy to answer anything else. One of my favorite pedals.

 

[cylnplnt]

Will post a build report when I finish

 

[amorapotter]

I'm not sure what those little numbers mean. I only pay attention to those if there's more than 2, like an IC chip or something which has 8 legs.

If your PCB doesn't have markings, you will need to trace the circuit connections to verify which pad is more positive.

sprunki retake​