MXR noise gate line driver repair

[BrunoFerreira]

I know this thread is old but i need some help.

I have an old block logo MXR Noise Gate Line Driver that does not work.
I've found one blue diode (i think it is a diode) with one black stripe and i need to put another in there because the old one fell apart through time.
The problem is that i do not know what diode i could use to fix the MXR.

In this thread https://www.diystompboxes.com/smfforum/index.php?topic=104211.0 MrStab has made a picture showing it and even there is a foto here https://www.dropbox.com/s/hjhovm23d71arb6/2.jpg


Thanks

picture of MrStab here also:

[antonis]

Original MXR Nose gate schematic https://benadrianaudio.wordpress.com/2010/06/29/mxr-noise-gate-now-with-more-flatness/ calls for 1N5331 Power Rectifier Diode..

IMHO, any kind of Si diode (e.g. 1N400X or even 1N4148/1N914) should work fine..

[BrunoFerreira]

Thank you Antonis

[BrunoFerreira]

Antonis, i  have 1N448 diodes around, so you think this will work fine as a substitute?

[antonis]

If you mean 1N4148, yes..
(proceed with no fear - after all, there is nothing you can damage..)

[BrunoFerreira]

No, i really mean 1N448

[BrunoFerreira]

I guess the 1N448 will not work since you have not replied.

I will try the others you point me to. Thanks again Antonis

[Fender3D]

Watch out!!!
diode is 1N5231B NOT 1N5331, and it's a Zener diode not a power rectifier.
If you look at schematic, albeit uncorrect, it sets bias voltage.
Any 5.1V zener will work

[BrunoFerreira]

I've used a 1N4004 and it lets the signal to pass (thanks Antonis) but when i hit the Switch on it does nothing, moving the pot left or right does nothing to sound. 

Does anyone knows what could be the problem?

[BrunoFerreira]

Watch out!!!
diode is 1N5231B NOT 1N5331, and it's a Zener diode not a power rectifier.
If you look at schematic, albeit uncorrect, it sets bias voltage.
Any 5.1V zener will work

Oh     can it damage the pedal or the amp since i did put an 1N4004 there?

[Fender3D]

Oh     can it damage the pedal or the amp since i did put an 1N4004 there?

Nope.
It simply just won't work...

[BrunoFerreira]

Oh     can it damage the pedal or the amp since i did put an 1N4004 there?

Nope.
It simply just won't work...

Thank you Fender3D

Watch out!!!
diode is 1N5231B NOT 1N5331, and it's a Zener diode not a power rectifier.
If you look at schematic, albeit uncorrect, it sets bias voltage.
Any 5.1V zener will work

Can you tell me the correct watts?
Also the other diode on MXR is the same or another model, if another can you tell me the correct?

[antonis]

Can you tell me the correct watts?

Less than 1mW..
Any 5.1V handy Zener should be fine..

Also the other diode on MXR is the same or another model, if another can you tell me the correct?

Can't find any reliable diagram with second diode..

[antonis]

I've used a 1N4004 and it lets the signal to pass (thanks Antonis) but when i hit the Switch on it does nothing, moving the pot left or right does nothing to sound. 
Does anyone knows what could be the problem?

Federico already explained it to you..

That diode actually is a Zener which sets T1 bias (Emitter sits at slightly lower than 4.5V, which is almost ideal for T1 configuration..)
In case of that diode is an ordinary rectifier, T1 Emitter is biased from +9V via R22 (with negligible voltage drop) resulting into almost topping T1 Emitter..
(no room for signal positive waveform swing)

[BrunoFerreira]

Thanks again Antonis

[BrunoFerreira]

Now it works, thanks again Antonis and Fender 3D.