Klon overdrive pedal diode question

[punkykatt]

A friend brought me a home made copy of what is suppose to be a Klon overdrive pedal. Problem: turn on the OD and the led flashes and makes a terrible sound in the amp with each flash. Pulled the guts and found a shorted diode (one of those orange glass ones) pulled the diode and using 2 magnifying glasses looks like it might be a 1N4739A .  I did not have one in stock so for ha ha`s I installed a 1N4148/1N914  and the pedal works fine.  Will the 1N4148 last? I tried comparing data sheets, the 1N4739A is a zener and the 1N4148 is a signal switching type diode. The data sheets tech values were confusing. Any help is much appreciated. Thanks you in advance. .

[sluckey]

A 1N4148 is ***NOT*** a substitute for any Zener diode.

[punkykatt]

Thats what I figured, but why is it working?

[sluckey]

I bet you connected the striped end of the 1N4148 just like the Zener was connected? If that's the case, then that's probably the answer too. Zeners are meant to be used in a reverse bias condition. When the reverse bias voltage is exceeded, the Zener avalanches (breaks down) and leaves the voltage at the Zener rated voltage (assuming there is a current limiting series resistor, not always apparent). Replacing the Zener with a regular diode and connecting the band end the same, the regular diode will be reverse biased and you effectively have an open circuit. I bet your circuit will operate about the same if you remove the 1N4148.

If your Zener diode really is a 1N4739A then it's a 9.1V 1W Zener. It may just be used in the power supply line to regulate the DC input power to 9V.

Seeing your schematic would be mighty useful!

[punkykatt]

https://guitargearfinder.com/wp-content/uploads/2018/11/klon-centaur-schematic-high-res.jpg   


Above is the only Klon schematic I can fine. They do show a zener 1N4742  12v in the power supply.  Yes I did install the 1N4148 in the same banded position as the 1N4739A was.

[sluckey]

D4 is used to prevent the dc from ever exceeding 12v. That's not an issue if you are using a 9V battery. Your 1N4148 is doing nothing.

If you will only power this pedal from a 9V battery don't worry. If you will power this pedal from a power supply, you should use a 12V Zener for D4 to provide some protection from overvoltage.

[punkykatt]

This pedal has no room for a battery. I will order the 1N4742 zener. Thank you very much Steve for your time, help and valuable info.