Behringer Octave Divider with shorted unknown diode

[Calambres]

Someone gave me a non functional Behringer Octave Divider. Upon inspection I found that a diode (D4) is shorted. It is a glass SMD non labeled small diode.



I have no idea what part it can be. I put there an SMD 1N4148 and the pedal worked again but it seems the tracking of the audio signal is a bit sub optimal.

Anyone know what this diode can be?... It is in parallel with another bulky diode: D3, an SS14 (1A, 40V Schottky)

[EDIT]: No, it is NOT in parallel with D3.

Maybe a Zener?

Thanks a lot in advance.

 

[jwin615]

Check the schematic of the original

https://www.freestompboxes.org/viewtopic.php?t=2747

The tracking may be a feature. not a bug.

 

[Calambres]

Thanks, but that is the schematic for the original Mu-Tron, not the Behringer.
Albeit it is a clone it is not 100% identical.

 

[Robert]

Got a pic of where it's located on the PCB?

What was the pedal doing before you replaced the diode?

 

[finebyfine]

I think there’s some germanium diodes in the original, maybe its an smd equivalent of a bat41 or similar low Vf diode?

 

[jwin615]

Not trying to be a jerk but we're gonna need something more than a pic of an unmarked generic diode.
If you trace the surrounding components and reference the OG schematic, maybe you/we can determine where in the circuit it is, what it's function is, and a suitable replacement.
Otherwise,

 

[Calambres]

The PCB, at least the main PCB (the other is for the foot pedals):



On the center-right, just above the red toggle switch (Power ON) there are two diodes, a black somewhat bulky D3 (PJ21BM = Schottky 1A 40V) and a little reddish glass diode D4, which is the one that was broken and I substituted for a typical 1N4148.



What's above the red toggle is what I presume to be the power section. IC1 is a TC1044SC, a charge pump to obtain symmetric voltage. The lytics are all 47uF, 25V. I'm pretty sure D4 must be a Zener but no idea what voltage.

 

[Calambres]

Reading the datasheet for the TC1044SC, the absolute maximun voltage input is 13V so perhaps D4 must be a near 12V zener?

The pedal has a label near the power connector indicating 9V-12V

The supplied wall wart outputs 9V 650mA

 

[Robert]

Check to see if it's across VCC.

Anode should be connected to IC1 Pin 3, Cathode to Pin 8.

 

[Calambres]

Anode should be connected to IC1 Pin 3, Cathode to Pin 8.

Yep!... exactly that!

 

[finebyfine]

I bet the previous owner read 9-12V as 9-18V and fried the 12V zener

 

[Nostradoomus]

I bet the previous owner read 9-12V as 9-18V and fried the 12V zener

This is probably it

 

[Calambres]

End of story: I put there a 12V Zener diode and the effect is now working fine.

Thanks to all for the clues.