Mini Me Chorus (solved)

[Anonymous]

Hey Guys,

this is my first post in this forum and I assure you, i did a lot of research on youtube and here bevor I registered to post here :)I just “build” the Mini Me. I build boosters, overdrives, fuzzes etc. but never something this complicated.
So here is the problem: In bypass mode, guitar sound goes clean through. When I engange the pedal, nothing so good. I know this is a common problem but no solutions here worked for me. I mesured the voltages on the pcb (ic’s and transistor’s) and they are strangely low or not there at all. On some restistors who should be directly connected to 9v there are just about 0,5 ore something like that. Online R31 has 9v
I made two mistakes: I put on the potentiometers before diagnosing which makes things for me more difficult and I put the jumpers for the 3207 on the wrong side of the pcb (they are directly under the ic socket but I assure that they are correctly oriented)

I have no idea how to proceed and desperate for help so im glad to hear your tipps.

[Billy]

Welcome to the forum Johhny

At a quick glance your R31 is a 47K ohm resistor should be 47 ohm so 47000 instead of 47

The colour bandings for a metal film 47 ohm 5 band resistor should be yellow purple black black brown or yellow purple black gold brown

That would stop you getting full voltage it being a wee bit larger

Your IC4 also appears to be the wrong way round your notch should be at the bottom

The most common problems in debugging are quite often incorrect component  values and orientation or dry solder joints, not always but usually

I’d advise checking all component values and orientation to the build doc

Use Barry’s handy resistor and capacitor chart here

The GUIDES PAGE – Mandatory Reading for all!

Or a calculator like this

https://samstechlib.com/610938/en/

I’m at work so haven’t checked in detail but as I said at a glance and from your information I quickly noticed these 2 problems

 

[Anonymous]

Hey Billy,

thank you so much for the quick reply. And you where correct: Just had to switch the resistors an the IC4 orientation and know it works and sound wounderful! Sorry to bother you with obvious problems like this. In the future I will look more closely but im eager to build my next pedal 🙂 and im glad that I registered in this great and activ forum.

Thanks!

[Billy]

It’s no problem Johhny that’s what we’re here for, glad you got it working it’s my favourite chorus

It’s not an obvious problem at all, we all do it regardless of experience and sometimes we don’t see it no matter how many times we look

You will find that the 3 things I mentioned are frequently the cause of non working builds so that’s why I mentioned it, if any of mine don’t work I’ll check the wiring first then do a visual check of both sides of the pcb to make sure all the values and orientation are correct and there’s no dry solder joints or solder bridges

Next thing I do is check power in as you did and all other voltages you’ll see reference voltage flags on the schematic VB, 9V etc so you can check voltage at those points

If you look at the power section of the schematic bottom right you’ll see 9v going in through your 47 ohm resistor along to some filter caps C13 and 14 then you’ll see IC1 and 4 pins 8 to v+ and 4 to v- telling you you should get v+ on both pin 8s around 9v and ground 0 volts on pin 4s

From there it goes along to a voltage divider R32 and 33 both the same value which would half exactly your +9v giving you your VB voltage bias of around 4.5v so you’d then know what you should get on anything marked VB

So you were on the right track recognising there was a problem at R31 all you would do then is check everything around that part of the circuit and trace it back hopefully finding you’re problem

 

 

 

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