Problem with Low Tide Modulator Footwitch

[funktor]

Hey, first post on the forum and first Pedal PCB build!

I recently finished building the Low Tide Modulator from a kit from musikding.de. Everything seemed fine, power not shorted, presumably correct voltages on the IC sockets (before plugging in the chips), and the LED gets power. But when I finally started testing with audio, there was no sound when the footswitch was in active mode, while bypass worked.

I started checking the continuity between different parts of the circuit, and I noticed that the tip and sleeve (audio in and ground) are shorted when the switch is in the on mode. I think I might have connected the switch incorrectly. The kit came with the 3PDT Breakout Board (https://www.pedalpcb.com/product/pcb126/), while the build instructions specify connections straight to the switch pins. I assumed that the breakout board should be connected in the same order as the holes on the main PCB, see pictures, but I might be wrong here?

If someone could confirm what the order of the holes on the Low Tide PCB is, I would be very grateful!

And it would be nice to know what the V+ and V- voltages on the chips should be, my readings on LM13700N were slightly strange (quite close to each other).

 

[Cybercow]

Start by checking the voltage supply rails - especially the +5V distributions.

Then if the voltage runs seem fine, using the schematic and an audio probe trace the audio path for signal starting at the input.

 

[Vild]

I spy a missing transistor in the second pic. Might have something to do with it.

 

[jimilee]

Sounds like you might have a solder bridge, if those transistors are supposed to be missing. What’s the back look like?

 

[Cybercow]

I spy a missing transistor in the second pic. Might have something to do with it.

I get the impression that the missing Q1 is actually an SMD JFET soldered onto the board. A better pic would tell.

 

[funktor]

I spy a missing transistor in the second pic. Might have something to do with it.

There are two options for the 2SK208 transistor, either through-hole or SMD. SMD version came with the kit. It’s not easily spotted on those pictures.

 

[dcfvgb]

Sounds like you might have a solder bridge, if those transistors are supposed to be missing. What’s the back look like?

This ^

I've had solder bridges under the foot sw boards, the input and ground (tip and sleeve) on the pcb (they are close)
Are there dust seals on the back of the pots? An insulator on the back of the dual pot (Slew)?

schematic

Low Tide Modulator - PedalPCB.com

Compare to Fairfield Circuitry Shallow Water

www.pedalpcb.com

measuring from the supply pin to the DC jack ground:

IC2 pin 8 5V
IC3 pin 11 8.85V
IC4 pin 8 8.85V
IC5 pin 8 5V
IC6 pin 16 5V
IC7 pin 5 5V
pin 4 4.7V

You mentioned odd volts on the 13700 (IC3)
If IC3 (13700) pin 11 is not appox 9V pull it and measure pin 11 at the socket.
If the socket reads approx 9V its a bad chip
If the socket reads something else measure contiuity from the VCC (9V) rail to the socket

You can test the randomizer and clock circuit with a MM. Turn the rate down, measure IC2 (randomizer eprom) pin 5 to gnd should see ramping up and down from appox 1 to 3 Vdc, changes faster or slower by the rate control.
That feeds the mcp602 ---> 4046 --> 3207. If the clock circuit is working, IC7 (3207 BBD) pins 2 and 6 to gnd will have a small ac voltage ramping up and down approx 10mvac to 200mvac

That's what I see on my Low Tide.

 

[funktor]

This ^

I've had solder bridges under the foot sw boards, the input and ground (tip and sleeve) on the pcb (they are close)
Are there dust seals on the back of the pots? An insulator on the back of the dual pot (Slew)?

schematic

Low Tide Modulator - PedalPCB.com

Compare to Fairfield Circuitry Shallow Water

www.pedalpcb.com

measuring from the supply pin to the DC jack ground:

IC2 pin 8 5V
IC3 pin 11 8.85V
IC4 pin 8 8.85V
IC5 pin 8 5V
IC6 pin 16 5V
IC7 pin 5 5V
pin 4 4.7V

You mentioned odd volts on the 13700 (IC3)
If IC3 (13700) pin 11 is not appox 9V pull it and measure pin 11 at the socket.
If the socket reads approx 9V its a bad chip
If the socket reads something else measure contiuity from the VCC (9V) rail to the socket

You can test the randomizer and clock circuit with a MM. Turn the rate down, measure IC2 (randomizer eprom) pin 5 to gnd should see ramping up and down from appox 1 to 3 Vdc, changes faster or slower by the rate control.
That feeds the mcp602 ---> 4046 --> 3207. If the clock circuit is working, IC7 (3207 BBD) pins 2 and 6 to gnd will have a small ac voltage ramping up and down approx 10mvac to 200mvac

That's what I see on my Low Tide.

Thanks for the detailed description!

Yes, I believe there was a solder bridge somewhere on the switch breakout board. I replaced the switch yesterday and the input socket tip is no longer shorted to ground. I have insulation on the back of the pots.

I didn’t have time to finish the work, but I’ll reconnect everything tomorrow and perform the tests you suggested.