No sound when pedal is off

ICBM

It’s hard to trace because all the wiring is white, but if it is wired correctly and nothing is touching where it shouldn’t be - which is also hard to be sure, but appears not - then it can only be a faulty jack. The switch appears to be wired right. (Or at least right in the less optimal true bypass scheme.)

djspecialist

ICBM said:

It’s hard to trace because all the wiring is white, but if it is wired correctly and nothing is touching where it shouldn’t be - which is also hard to be sure, but appears not - then it can only be a faulty jack. The switch appears to be wired right. (Or at least right in the less optimal true bypass scheme.)

I'll try reflowing the connections on the jacks.

ICBM

djspecialist said:

I'll try reflowing the connections on the jacks.

Don’t bother, it’s not that.

If the wiring is correct and nothing is touching anything it shouldn’t be, and it’s still sucking tone, one of the jacks is partially shorted.

First check if the contact on the output jack is touching the back of the pot when a plug is in it first. Pull the wiring gently so you can see where the individual wires go, and make sure the two wires from the tip contacts on the jacks go to the middle terminals on each side of the switch, and there are no other connections to them.

djspecialist

@ICBM is there some way I can use a multimeter to test whether one of the jacks is partially shorted?

ICBM

djspecialist said:

@ICBM is there some way I can use a multimeter to test whether one of the jacks is partially shorted?

Yes - set the pedal to bypass and measure the resistance between the tip contact of either of the jacks and ground. If it’s not infinite (no reading on the highest scale) then there’s a short. If there is, you’ll need to unsolder one of them from the switch to find out which.

djspecialist

ICBM said:

First check if the contact on the output jack is touching the back of the pot when a plug is in it first.

It's not.  In any case, the pots have plastic covers.

ICBM said:

Pull the wiring gently so you can see where the individual wires go, and make sure the two wires from the tip contacts on the jacks go to the middle terminals on each side of the switch, and there are no other connections to them.

That seems to be the case:

ICBM said:

set the pedal to bypass and measure the resistance between the tip contact of either of the jacks and ground. If it’s not infinite (no reading on the highest scale) then there’s a short.

Here are the readings from the meter:

When bypassed:
Input tip to ground: 100k when volume pot on max, 0 when volume pot on min
Output tip to ground: 100k when volume pot on max, 0 when volume pot on min

When engaged:
Input tip to ground: 100k when volume pot on max, 0 when volume pot on min
Output tip to ground: 1000k regardless of volume pot setting

So I think there is a short.

ICBM said:

If there is [a short], you’ll need to unsolder one of them from the switch to find out which.

Which wire(s) should I unsolder?

One final observation: if I pull gently upwards on the connection from the wire marked "output tip" above into the switch, the short goes away (output tip to ground measurement goes to INF).  I can't reproduce this effect (by pulling on any of the switch connections) for the input tip to ground measurement.

ICBM

djspecialist said:

When bypassed:
Input tip to ground: 100k when volume pot on max, 0 when volume pot on min
Output tip to ground: 100k when volume pot on max, 0 when volume pot on min

...

One final observation: if I pull gently upwards on the connection from the wire marked "output tip" above into the switch, the short goes away (output tip to ground measurement goes to INF).  I can't reproduce this effect (by pulling on any of the switch connections) for the input tip to ground measurement.

It sounds like the switch is buggered. What's happening is that the connection between the right middle and right top terminals is still active in bypass, so the volume pot is loading the bypass signal.

(The labels are hopefully incorrect by the way - the middle one on the left should go to the input tip, not the power negative.)

djspecialist

ICBM said:

It sounds like the switch is buggered. What's happening is that the connection between the right middle and right top terminals is still active in bypass, so the volume pot is loading the bypass signal.

The wierd thing is, this is the same behaviour I saw before I replaced the switch - so if you're right I'm very unlucky that a new switch failed in exactly the same way as the old one

If the output jack was faulty, with a partial short between the tip and sleeve, would that cause the same tone suck when in bypass?

ICBM said:

(The labels are hopefully incorrect by the way - the middle one on the left should go to the input tip, not the power negative.)

Oops, you're right of course.

ICBM

djspecialist said:

If the output jack was faulty, with a partial short between the tip and sleeve, would that cause the same tone suck when in bypass?

No, because it wouldn't be affected by the volume pot.

When the pedal is (true) bypassed there are only three components in the circuit - the jacks and the switch. If there is a fault - and assuming the wiring is correct - it can only be one of these.

Are you absolutely certain you didn't accidentally refit the old switch?

djspecialist

ICBM said:

Are you absolutely certain you didn't accidentally refit the old switch?

Yes.

Looks like I need to buy another switch then ...

ICBM

It does seem very unlikely, even given the general crapness of 3PDTs. But I'm reasonably sure you've eliminated every other possibility, unless the wire from the switch to the jack and volume pot are shorting against each other somewhere under the board, which doesn't seem likely either!

Temporarily disconnect the wire to the volume pot and see if the tone suck is gone in bypass. (The pedal won't work when it's on.)

djspecialist

ICBM said:

Temporarily disconnect the wire to the volume pot and see if the tone suck is gone in bypass. (The pedal won't work when it's on.)

After disconnecting that wire, the tone suck in bypass is gone.  (And there is no sound when engaged, as you said.)

ICBM

djspecialist said:

After disconnecting that wire, the tone suck in bypass is gone.  (And there is no sound when engaged, as you said.)

It's got to be the switch then. If the short was in the wires under the board it would still be there even with the switch disconnected.

Is it from the same batch as the original? It seems beyond any sort of believable coincidence otherwise!

exocet

Perhaps the switch was "cooked" when you replaced it? Try not to overheat it when soldering the connections. Perhaps leave it to cool in between making each connection.

djspecialist

It was the switch.  I just installed a new one (being *very* careful not to fry it while soldering) and the tone suck is gone

Next question: after all that, do I actually like the pedal when I give it a proper try at next week's band practice ... ?

ICBM

Now you know why I detest 3PDTs.