Recurring Nightmare Delay - Oscillation, No Signal/Effect

[sticky1138]

Just finished this FuzzDog Recurring Nightmare, which is a DBA Echo Dream clone. Fired it up and it’s not functioning properly.

There is no dry guitar or delay effect coming through, but there is oscillation that responds according to all the controls. Volume/Mix/Fuzz pots each affect the oscillation volume, Rate/Time/Depth control the shape, switches have some audible effect, etc.

My first thought was a fake/bad 2206 chip, but it is from Jameco, which appears to be a reputable dealer. I also tried a couple from Amazon (!) for shits and giggles, and they behave the same.

To anyone familiar with how PT2399 circuits work, based on the output I’m getting, what should I be investigating?

• I am using my usual test rig. It functions normally with every other working circuit.
• As far as I know, referencing pics of others’ successful builds, my components are correct.
• Tilting up the pots, I don’t see any cold joints or bridges, but I haven’t removed them for a deep inspection. (Not looking forward to that because I used lead-free solder!)
• It’s looks like a tight fit, but that 5817 is not touching the pot legs.

 

[Erik S]

Your soldering looks nice, your board is clean, your picture is clear, you used caps on your pots. For a post in the troubleshooting section you're already winning!

There is no dry guitar or delay effect coming through

Just to be clear, are you getting signal through when it's bypassed? Just nothing when you engage it?

Nothing's jumping out at me - all the IC pins in their holes? No sneaky ones folded under?

 

[sticky1138]

Yep, original signal goes through when bypassed. All pins in the holes and I quadruple-checked orientation.

 

[z2amiller]

Have you tried an audio probe, to see where the "good" signal dies and you pick up the noise?
That's a super handy way to help narrow down the problem. Your soldering looks nice and clean.
It's possible that there's something going on under one of the sockets, though :-(
You could try to use a multimeter and see if there is continuity between any of the nearby pins in each socket.

When you say you hear an oscillation no matter what's going on with the knobs, it makes me think that
there's some leakage from the signal generator (IC1) into your audio path. If the wet/dry switch doesn't
change anything, I think that narrows it down to a pretty small section, maybe something shorting against
the fuzz or volume pots?

Also I have to take a moment to appreciate the PPCB layouts (almost?) always having the
polarized caps in the same orientation. Having the electrolytics pointed every which
way on this board is a giant footgun.