Effect switching issue

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BKPoe

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Here is a strange one. I built an Arum (Golden Pearl) a few years ago and had it on my board for a ling time. It was in a loop switcher, so it was always on. One day it went in and out a few times and then quit.

I pulled it out to troubleshoot the other day and when bypassed, I have signal going through, but when I hit the switch, I get nothing. I put a 1K tone on the input and started tracing the signal and had the tone in several places so I thought I'd start at the end and work back. I have the tone on the output jack and the POTs affect the tone. So I know the effect is working, but when I plug the guitar back in, there is no signal when the effect is switched in.

Any thoughts?
 
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BKPoe said:
Here is a strange one. I built an Arum (Golden Pearl) a few years ago and had it on my board for a ling time. It was in a loop switcher, so it was always on. One day it went in and out a few times and then quit.

I pulled it out to troubleshoot the other day and when bypassed, I have signal going through, but when I hit the switch, I get nothing. I put a 1K tone on the input and started tracing the signal and had the tone in several places so I thought I'd start at the end and work back. I have the tone on the output jack and the POTs affect the tone. So I know the effect is working, but when I plug the guitar back in, there is no signal when the effect is switched in.

Any thoughts?
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Footswitch maybe?
 
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I can attest to stuff laying fallow eventually not working, even though you might assume since it's not used (in this case always on with your loop-switcher handling turning it "off/on") that it isn't suffering any wear & tear.

I had solderless patch-cables go bad on my at-home board, which rarely moved, occasionally slid it under a sofa-bed when guests visited.

So perhaps your switch in the pedal-in-question has succumbed to some rusty contact points or what I don't know, but...

From your description, sounds like a physical problem — I'd check the input jack, I've had problems with cheap jacks, too.
 
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jimilee said:
Yes, there are multiple parts to the switch. In one position the top 2 rows are connected, in the other the bottom two rows. Reflow the switch or make an audio probe to check it out.
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I was using a probe when I checked it out and with the effect on, it won't pass the sound from the guitar but will pass a tone from my phone.
 
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Jack/cable/solder joint/grounded signal issue .
Plug a cable in both ends and put it in bypass. Test resistance from tip to tip of each cable. Should be <5 ohms or so, deducting your lead resistance from that measurement. I would also check input tip to ground and output tip to ground. Those should be open Or in the megaohms range.

I suspect your issue is on the input side if you can inject signal and get output. Either a cable or the jack or jack shorting.
 
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jimilee said:
I’m with you. Nothing makes sense here. The effect only passes signal with your phone plugged in but not your guitar.
Click to expand...

There be may a klew, the phone...

Maybe the phone is TRS, whereas the guitar is vacant in the "R" with just TS.

I've come across some odd behaviour in the past that involved TRS getting mixed in with TS (or was it TS in with TRS?).
 
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I repaired a pedal for someone recently that behaved similar. No signal with guitar, but it would pass signal with my signal generator.

The input cap was leaky so the guitar pickups were loading down the VREF supply when a guitar was plugged in. To make matters worse, the capacitor measured perfectly fine out of the circuit. Replacing it corrected the issue.

If you have a DMM, check the DC voltage on both sides of C1 with a guitar plugged in.

You should have around 4.5VDC on one side, and near 0V on the other. If you do not, that should be investigated.
 
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Just to keep you from having to pull the PCB out of the enclosure to make that measurement...

Measure the voltage on the Left side of R1 (this is the input side of C1), then the Left side of R3 (this is the opamp side of C1).
 
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Robert said:
I repaired a pedal for someone recently that behaved similar. No signal with guitar, but it would pass signal with my signal generator.

The input cap was leaky so the guitar pickups were loading down the VREF supply when a guitar was plugged in. To make matters worse, the capacitor measured perfectly fine out of the circuit. Replacing it corrected the issue.

If you have a DMM, check the DC voltage on both sides of C1 with a guitar plugged in.

You should have around 4.5VDC on one side, and near 0V on the other. If you do not, that should be investigated.
Click to expand...
Thank you. This is awesome and the explanation finally makes this make sense. I hope to be able to look at it again this weekend. I've got a busy week ahead of me but I'm looking forward to trying what you suggest.
 
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