Strategy for connectivity testing and signal path

Started by matopotato, July 14, 2022, 03:15:08 PM

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matopotato

After having gone through a Blueshift (DC-2 clone) build where there is no chorus effect in the pedal I checked the pinned debug thread and got to @R.G. s http://www.geofex.com/fxdebug/fxdebug.htm but the "No or very little effect in the sound when the effect is engaged" seems unfinished. Or unstarted.
So my plan was to take the full journey, starting with connectivity testing with DMM through all connections on the board and marking up the schema.
Strategy was to measure from leg to leg where possible, and else (caps, jumpers etc) use the solder point.
But some way down that road I realized that in a crammed space it is easy to have the DMM probe tip touch the eyelet of the PCB instead, and that would only tell me that the PCB is ok for that connection.
I avoided the solder points since I thought that eyelet, solder and leg have to connect so if leg-to-leg is OK, the the others follow. Sort of.
But could a solder point have reached the eyelet, but not the leg, and the leg is firm in the eyelet?
I am beginning to think that it would be more telling to measure between solder points, thus avoiding the eyelet-eyelet risk of missing a cold solder.

If my concerns are confirmed here I'll take it through another round. But it takes a while so wanted to ask first what is the best strategy here. And this would apply to any connectivity research I guess.

Next for the Blueshift case if connectivity checks out a second round would be to "follow the signal path". I suppose if you are a diy pedal senior wizard it is a no-brainer. But for me still in the learning phase I wonder if there are any general guidelines for how to figure out the "Signal Path".
I understand it begins at Input and ends at Output, and that the power stage is not really signal path (?). But the rest? I mean all is after all connected.

Thanks
"Should have breadboarded it first"

Kevin Mitchell

#1
With a build like - being a BBD effect, very tight layout, stacked PCBs, hand wired jacks & footswitch and also having options of opto or true bypass it can be very easy for an error to happen.

Are you calibrating it by ear or with a scope?

Think of the circuit & schematic in blocks. Probe the input & output of each device along the signal path.

Typically you'd want to check the BBDs first just to see if it's biased & passing signal. Assuming you don't have an oscilloscope, audio probe pins 7/8 (they're shorted) of both 3207 chips and adjust the bias (TR1 for IC9 & TR2 for IC3) for the most clean signal.
If the signal isn't showing on pins 7/8, probe pin 3 to make sure it's present on the input.

Let us know what you find and we can advise further.
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matopotato

Quote from: Kevin Mitchell on July 14, 2022, 03:54:33 PM
With a build like - being a BBD effect, very tight layout, stacked PCBs, hand wired jacks & footswitch and also having options of opto or true bypass it can be very easy for an error to happen.

Are you calibrating it by ear or with a scope?

Think of the circuit & schematic in blocks. Probe the input & output of each device along the signal path.

Typically you'd want to check the BBDs first just to see if it's biased & passing signal. Assuming you don't have an oscilloscope, audio probe pins 7/8 (they're shorted) of both 3207 chips and adjust the bias (TR1 for IC9 & TR2 for IC3) for the most clean signal.
If the signal isn't showing on pins 7/8, probe pin 3 to make sure it's present on the input.

Let us know what you find and we can advise further.
Tha ks, I first did by ear. And it is not much to calibrate as there is no chorus effect no matter how I turn the trimmers. If I could detect any notion of chorus, I  would be more careful and put in a 1ch scope.
I'll årobe and measure pins as well.
I just wanted to hear if there were any strategies or thoughts on a more general note for connectivity tests.
I think (was a while ago) that some of the ICs on second deck did not carry signal on any pin. This made me check connectivity.from start to finish, but one small suspected solder was the only outcome. Which lead me to open this thread.
"Should have breadboarded it first"

Rob Strand

Send:     . .- .-. - .... / - --- / --. --- .-. -
According to the water analogy of electricity, transistor leakage is caused by holes.

anotherjim

It's usually helpful to disable the clean signal from the output of any delay-based effect. Going by the Boss schematic, I think lifting one end of R71 and R92 will stop the clean from reaching the outputs. Then you can concentrate on getting audio paths through the delays.

The two clock signals for the BBD chips read on a DMM set for DC voltage at near half the clock generators supply voltage which can be useful if you don't have an oscilloscope. If one is full supply and the other is zero volts, the clock is stopped.