Opinions please

[CeaSaR]

Hello again my friends.

My son purchased an acoustic guitar with a Belcat AT-3000 piezo pickup/eq, non functional of course.
Looking over the simple PCB, there isn't much to go wrong - 2 active devices, resistors, caps and a mystery
cylinder (I think it's a diode). Sliders work, rough measured the other passives but couldn't check the actives
well. Only out of spec resistor is a 103 that measures about 5.8K. No luck finding a schematic. Other troubleshooting
consisted of running the sliders while plugged into an amp. Scratchy noises but no guitar sounds. Replacement
AT-3000's are only available overseas and shipping doubles the price. Repair should be a minimal cost. Heck,
a complete rebuild should only cost a few dollars. Actives are all SMT, opamp is 4558, transistor is a 3906.

I would like your opinions on what I should do for repair and what is the mystery cylinder.

Photos:






Interesting note, the first photo is with regular fluorescent lighting. The 2 subsequent ones are with LED spotlighting,
AKA a handheld LED flashlight. Makes a big difference in the readability of the labeling.

Website: http://belcat.com/html/products/preamp/at3000.html

CeaSaR

[Janitor Tzap]

The circuit seems fairly simple.

Check the connections from the board to the piezo pickup.
It may just be a bad wire, or bad piezo pickup.
Try injecting a signal at the point the wires are soldered to the board.
If you got signal, then try at the piezo pickup.
No signal, bad wire.
Signal, bad piezo pickup.

If you have no signal at the points where the wire from the piezo pickup connect to the board.
Try injecting a signal into the inputs of the 4558.

Too see if your get anything out of the chip, and test the 2N3906 too see if it is good.

Break out the ESR Meter and test the electrolytic capacitors.
They do have a tendency to go bad.

Good luck troubleshooting it!


Signed: Janitor Tzap

[dacflyer]

the cylinder like object i am guessing that your referring to..looks to be either a signal or zener dioad..
I agree with Janitor, i'd test the board 1st,, maybe substitute a input signal in place of the pickups
and see what you get..i am sure there is more than 1 pick up on the guitar, so unlikely that they both are bad.. a bad connection is possible, most likely a bad OPamp is the culprit. but you can figure that out. there is not much to that. should be easy to bug out.
good luck.

[Janitor Tzap]

Oops,
I forgot about the cylinder object.

Yes,
I agree with dacflyer that it is a diode.
The violet stripe indicates the cathode on it.

But what type of diode is, I can't tell.
There are no other markings, other than the violet stripe.


Signed: Janitor Tzap

[Robert Reed]

OR--- Maybe 'Lytics with the negative polarity stripe. I cant envision any use for diodes here and especially in that size.

[Dean Huster]

If the board is that simple, reverse-engineer a schematic so you can see how the diode fits into the circuit and maybe determine what kind it is.