Newly assembled Shruthi Not working

SO my control board boots and works great but the filter section doesn’t seem to work at all, I could get the test note by pressing and holding the first button but it was weak and no filter control… I opened her back up and initially i was having -5v rail problem and fixed that. but still no filter and now the test note wont come on. Strangely when i hold the Bottom Pcb in my hand and it makes contact both the synth and filter seem to work all be it faintly. Sorry for what is prolly something i messed up on my part.

here is a picture of both the top and bottom of the filter board.



any and all help is appreciated


Can you check at which points you get good signal?

Hi thanks for the fast response! I gather from another post im supposed to be listeing to the audio signal at these points. What exactly should i be listening for? should it also only be the powered filter board no controller attached?

The control board should be attached, and you should play a note. This picture is from the bottom of the filter board assembly instructions page - have a look, there are further descriptions of what kind of signals you are supposed to hear at each point.

More practically, when you do this, try bending a bit the connector sandwiched between the two boards, or if you have hookup/jumper wires, use them.

i am only getting a signal on 1 and 2.

i didnt realize there was more info on the assembly page. as i suspected there is a problem with my filter. i will probe now for continuity on the Ic and associated components.

alright making progress. I got the audio to get all the way to 7 but does not show up on 8 and im having trouble finding the problem. What is the signal chain the resistor on 7 takes to 8 the graphic isnt clearing it up for me.

There’s nothing you can really test in between point 7 and 8. This is the VCA. Maybe check that the voltage on the VCA> pin goes up while a key is pressed (the actual voltage depends on the sustain setting) - expect something like 3 or 4V.

well my voltage went down from 2.48 to 2.40

You mean it’s 2.48V by default and it goes down when you press a key? This is not normal… Are you sure you’re checking the right pin?

oops you are correct i was checking osc not vca. vca doesnt read anything.

Are you reading on the filter board or the control board?

If it’s 0V on the filter board but OK on the control board -> connection problem between the boards, or badly soldered header.

If it’s 0V on both boards -> bad solder joint on the MCU, or maybe a MCU pin got bent when you inserted the chip.

its is 0 on both boards. By MCU you mean the main controll chip(the big one) so ill have to remove the screen to access the solder joints?

i hope you socketed the big one? first check if all pins go into the socket.

Looking at the image of the bottom of the board, the soldering of the TL072 socket might be dodgy. Could you resolder that ?
Take out the TL072 before soldering, perhaps, unless you do it quickly.

Can confirm OpAmps tend to die while soldering… thats why i get them by 100s :wink:

You can measure continuity from the pin of the ATMega to the solder joint in the connector.
Use the diode setting on your multimeter so it will beep when there is continuity. I think you will be able to fix it without having to remove the display.

It also looks like diode D1 isnt soldered
and id redo the soldering on the 10k resistor above the bottom left LM13700N chip

Opamps are also super useful that’s why I have so many! Thank you for all the advice I shall use it all and report back! And yes I socketed everything.

So I got a reading in vca now. It drops from 3.20 down to 0.02.