Shruthi not Shruthing

I bought a second hand Arduino a few months back and (for an extra £20) the guy threw in a drawer-ful of electronic components and a few PCBs, one of which was (what appears to be) a fully built Shruthi!

I looked it up online and couldn’t believe my luck, it makes an awesome noise!

Only problem is, mine doesn’t :frowning:

It powers up and all the lights, knobs , buttons and panel seem to work but the only sound that seems to be coming out of it is a kind of rhythmic clicking.

Can anyone help? I’m not sure where to start.



The first step would be identifying what type of filterboard you have. Then, search for the schematics. Use an oscilloscope or a little probe wire connected to some speakers to check the signal-path.

Also: Give us some more information about what works and what doesn’t. Does it receive midi? Does the display and all the controls work?

Hi TheSlowGrowth, thanks for the response, I’ve got it hooked up directly to one of my studio monitor speakers, I held the first button on the left down for a few seconds and thats when the clicking noise begins.

I don’t have access to an oscilloscope and I’m not sure how to test if it’s receiving midi but the display and controls all appear to be working fine.

On closer inspection, It looks like there may be some components missing.

Here are photos of both boards:

It’s an SMR-4 (mk1) by the looks of it.

Looks complete, but the soldering is pretty sloppy (not enough solder in quite a lot of places …).

Should be fixable. Do take out the ICs before reflowing and/or adding solder.

The one pitfall might be the socket of the microcontroller (the large IC): you would need to take off the display to reflow the pins of the socket, which is NOT easy at all (and could destroy your board). Still, these might be fine (as you say that the lights come on and the buttons+panel seem to work), so worth trying to fix the rest.

Take all the chips out except the one in the PSU section and check the voltages.

Hm, regarding the ATMega i remember Olivier stating that in most cases the MCU does work or not at all. Given the fact that display and the menus are working, i would stay off that in first instance.

One thing to check first of all would be if the correct filter type has been set in the settings. Then measure the voltages as written in the troubleshooting section of the guide with all ICs removed except those of the power section. Then i would reflow all questionable solder points.
If all this is to no avail, the i would start probing the signal as stated in the guide to narrow down the problem to distinct areas.

The controller board seems to be working, so you should concentrate on the filter board.
Have a look at this page: SMR-4 filter board
Do the voltage testings at step 4, especially if the negative voltages are there.
Make sure the connection between the two boards is fine and resolder the joints which are looking suspicious.
If you connect a MIDI interface or keyboard to the MIDI In port and send a note on message, a note icon should appear on the right of the screen.

Thanks cj55 - I’ve tested the dots I could get to easily: the blues are at 0v but the reds are ~5.9V\ and\ the\ greens\ at~-5.9V. I’ve also connected a MIDI keyboard and I don’t see a note icon when I press a key. I’m not too confident resoldering just yet as it looks better than mine already. Is ther anything else I could try first?

Which firmware version is installed (should be shown during startup)?

As nightworxx already proposed: Which filter type is configured in the system settings (should be lpf for SMR4, see manual).

Then you could check continuity at the connections between the two boards.

If MIDI in is not working you could check if the signal is passing the optocoupler using a LED. Connect the LED between pin 5 (GND) and pin 6 of the 6N137/138. If you generate MIDI input you should see the LED flicker.

You can also start a note on the Shruthi by pressing the encoder for a couple of seconds - the Shruthi then plays a continuous note until you long-press the encoder again. That way you can test if its the filterboard that fails or the MIDI In circuit.

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