Fly Mojo - lost piezo sound

[Razoumihine]

Hello! Some days ago I fixed the tremolo that had a « post leaning » issue. To do so, i had to unweld the bridge cable from the PCB in order to dismantle the bridge.
After fixing the bridge thanks to @billy ’s tutorial, the bridge now rotates like a charm.
But when i re-welded back that bridge wire to the PCB, then the Piezo sound has gone.
I found the wiring diagram here and am not so sure to understand : are ground and bridge wire supposed to be welded together on the pcb? See attached image of the drawing and of my wiring now after having unwelded again…

#PiezoIssues

[Razoumihine]

Actual unwelded

[Razoumihine]

And re-welded same as it was before.
The Bridge and Neck pup work fine. But still no piezo.
Battery is new.
Is there is a way to check the piezo mic works fine?
Cheers
Lionel

[billy]

Hi Lionel

There is a shielded cable for the piezo and both conductor and braid look like they are shorted together from melted insulation.

Cut 5-10mm off the end so you have a blunt end. Then strip 10 mm of the outer jacket and you will see the braided shield. Carefully trim about 1/2 of that braid off.

Then you will see a sometimes translucent (yours is black) jacket below. Strip about 3 mm of that off and there should be a conductor there.

That inside conductor goes to the inner-most pad, solder carefully.

The braid goes to the pad on the corner.

Be careful not to get too hot or too much time so you don’t melt the inside jacket or damage a pad. You might have to adjust the position slightly to get the conductors where they need to be.

That should resolve your issue.

Good luck!

[mmmguitar]

@ Razoumihine, Just to tack some illustration on to Billy's helpful post:

The wire running from the summing board on the underside to the bridge to the Piezo input/ground pads on the Powerchip is a single conductor w/shield:

And here's how the shield and internal wire solder to the two pads (with all other connections labeled - click to enlarge):

Being as your Powerchip PCB seems especially burnt, corroded, and seemingly coated in excess flux, I'm curious as to whether you have a temperature control for your iron, or a grounding wedge tip? I think getting in there with a hot tip to quickly melt that blob and suck it up before it can burn the underlying traces or PCB might be safest. In any case, I recommend being prepared to suck all that excess solder off with a desoldering pump as soon as you get that blob to melt.Thankfully, in the worst case scenario, replacement Powerchips are still readily available.

[billy]

Thx for the added info Marc!

[Razoumihine]

Hello! Marc and Billy thank you very very much for your help, indeed, conductor and shield were connected and i didnt even … well… no comment
Yes the area looks not that nice, but now all is fixed and piezo works fine.
It is not easy easy cause the soldering iron i have has absolutely no regulation. Plus the area is small and heat up quickly. I was afraid to overheat everything and loose definitely the preamp.
But apparently the preamp is resistant enough, and now pup and piezo work fine!! It’s a relief!
Big thanks again!
Lionel