My first Shruthi-1 SMR4 is all built but MIDI doesnt work so far [solved]

Hi all, thanks to Oliver today I was able to get my Shruthi-1 assembled and powered up

Ive tried 3 different devices and 2 different MIDI cables and MIDI in/out doesnt work on my SMR4 , is there something thats usually overlooked by new DIY’ers? ( chips upside down or somesuch)

Also , when I try the input as a filter, the Noodle and Bleep ones dont affect the audio, they just generate there own loops of feedback and distortion , but only if I set the filter and resonance above 60 or so.

Thanks in advance for any assistance


I tried hitting S1 to generate a test tone and everything there works fantastic, all the envelopes and tweaks seem to work great, I can even get the sequencer to work too, so it IS generating sounds

Have you double checked the opto coupler, that’s the 8 pin IC closest to the MIDI sockets, and all component values around it?

Check the Diode, you could have reversed it. It will run without.

Also, you can sometimes get the eprom and the opto isolator mixed up. But make sure the resistors are the right value, the diode is facing the right way. The opto isolator is just an LED and photocell, if the LED isn’t producing enough light then you get no output from it, so the resistor value being correct is very important.

Ill check those things and get back to you , thanks all

ICs correct
Diode correct

but I had the resistors reversed, i had 2 brown bl bl red instead of the r r bl bl :frowning:

saying im total newbie at this, to desolder a resistor do i just apply the iron and then pull with some need nosed pliers? or can i cut away the leads and just put the new ones in?

My trouble is, I forgot to test it before mounting the LCD so the LCD is covering the back of the circuit board :frowning:

saying im total newbie at this, to desolder a resistor do i just apply the iron and then pull with some need nosed pliers?
you can try this way. A probably good idea would be to add some solder before you pull the resistor, so that the tin melts better and longer. Don’t overtry, if that doesn’t come, switch to plan B = cut the leads.

Ok ill try it and see :frowning:

Best not to cut the legs. Heat and pull.

The biggest problem is getting a small section of component leg out of a hole. Even with a desoldering tool it can be fiddly.

i managed to get the 3 resistors out , but I couldnt get them all to go back through the board , i ended up removing as much solder as I could and pushing the leads back into the molten solder to hold them in place and soldering 2 that way

The 3rd one I had to lay on its side and solder to the top of the board and hope that the solder would complete the circuit. Not the most professional way to do it but…now it works! w00h00

what a great community here on MI , thanks for all the help everyone

now I need to ressemble and take a shot for the completed Shruthi thread


If you use a pin or needle then you can clear the holes. Heat the pad and push in (holding the pin with pliers).

Make shure your rod is made of stainless steel (nice sentence before…) so it doesn’t stick to the solder.

I already put it together and filled in the engravings with white gloss paint, so hopefully those solder joints hold up…

FCD , the case looks fantastic BTW

here is a pic of it all setup , painted and polished

well done!

Nice, is that tangerine?


I think its called Orangina , its one I got from FCD72 it looks great with the engraving filled in I think

Tangerine is more . . . . kind of tangerine. Heres a Pic of a Case in Tangerine to compare.

It was called Orangina right Frank? it looks great