Short on filter board

Hello everybody,

I did a horrible mistake while I was trying for the first time the shruthi 4-pole mission.
First, I didn’t pay attention to the two leds at bottom of the filter board, which were not cut and could have touched
something like five resistors next to them, the connector G6, the capacitor C36 and the IC8.

In the first seconds I had a good sound but, while I was pushing S1 or S2 buttons, the LCD went off; I did that several times of course _'
and I saw that leds were lighting on and off; several times too…

Now, the sound of the shruthi is terribad and seems really digital, I don’t know the synth yet but something went wrong: I pushed the S1 button once and I felt like the sound was “broken”.

I checked some values on resistors and IC sockets:

everything was normal on the ICs, except that I didn’t do it on IC 8, 9 and 10 because I didn’t know where I had to put the multimeter.

Anyway, the values of resistors were really problematic:

220= good
220= good
68= good
82= good
100k= 54,7
100k= 54,7

What should I do next?

First you should understand that measuring Rs inside a Circuit is meaningless, as they build a Resistor Network thru the PCB thus you are not measuring the Resistance of a specific part but the REsistance of the Whole Circuit. So “Resistance is Futile”.

Next its unlikely you killed a resistor (it would be looking burnt), more likely you killed a chip…

Best would be you listen thru the Circuit to see where the path is broken and replace the faulty chip.

thank you for your answer

I found this link on the wiki

but I am not sure of what is the ground on the filter board and what are ring and tip on the jack
Can you explain it to me?

Thank you


if I know there is a hugo chance that the led legs touched the IC8, should I start by replacing this part especially?

And do you think a video which shows how the shruthi is responding can help someone to solve the problem?

Use as Ground any Pad labelled GND for exampele on the Expansion Port. Tip ist the little Part on the Top, Sleeve is the uppermost part (or the other one on a Mono Jack)

See here:

1= Sleeve 2 = Tip

Also do the power supplytesting on the build page


thank you for the link, but now I have a problem with the procedure. Because it seems that I need three jacks: two to touch the filter board and one to enter the mixer, am I right?

@shiftr do you have a link for the 4-pole because I am not able to succeed the fifth step: I don’t know where I have to test the voltage :confused:

You cut one cable and probe with the wire ends itself…

oh didn’t read very well …so 4PM

The following image shows where the power pins are located on the first row of ICs. Red: +5V ; Green: ground ; Blue: -5V.

Also, is the control board set to “4pm” in the filter setting menu?

Ok I’ll try that way! :slight_smile:

Another question: now that I have soldered the two LEDs, if I replace every IC with other ones from another shruthi, can I damage them? Because if something went wrong with an IC, I will be able to find which one directly


Oh! I checked these ones with a multimeter and they were all good!


not yet because I bought the wrong encoder…
but two hours before the short, the sound was really different, even if it wasn’t set on “4pm”. I tried with another 'pm filter board a friend has and he had exactly the sound I had before the possible short - even if, for both, sound was/is changing every time I push a button

But if you have it on the wrong filterboard setting it will sound terrible with lots of digital noise in it. And the noise reacts to presses of the buttons. If you hear it change with button pressing it is the filter setting for sure. Maybe it was on the right setting before the short?

Oh guys I see some hope here!

But there is still a problem: when I place my control board on the other filter board ( the one that didn’t receive the short), the sound is different and as it was before. If, as I believe, the control board is the one setting the “4pm”, the sound should be the same with the two filter boards, right?

RTFM for the 4PM :wink:
Since this Filter has 60 different settings so it can sound in various ways - most likely you just scrambled up your settings…
And you dont need the encoder to change them.

Ok, I’ll try to “reset” the original settings but still: the settings are stocked in the control board and the same settings applied a different sound on the other filter

Thank you for “RTFM”, I didn’t know the expression AND I read the manual ahahah :smiley:

Did you check the voltages after you had the short?

Wait, i can do better:


So the Filter works and you can hear a change when changing the “mod” and “fla” setting?

Did you trim both filters the same (RTF V/Oct Tuning Section. . . )

Sorry for late answer but I was away for some time :confused:

“Did you check the voltages after you had the short?”

Yes I did and everything was ok.

So, I RTFM, I set back the old settings and I am really confused… because sound is now pretty awesome _ I still have some lil’ things to check but the main trouble was the mod setting, indeed.

But I still hear a little problem and I’ll do the procedure you’ve been proposing me ( hearing the audio path) when I find the schematics for the 4-pole in the wiki.

Anyway, some things are weird ( especially when I push some buttons), but I need to read the manual properly before asking. Thank you for your help, I was mad about my mistakes

Thank you so much!