Build problem at the very last step

Hi everybody,

trying to build my very first Shruthi kit. I completed the filter board with no problem, checking the voltages as in the instructions. Everything was ok.

I then built the control board, and before soldering the LCD I connected the two boards and applied power. The LEDs were working as was described in the instructions as well as the encoder.

I then soldered the LCD and after that the LED’s don’t light up anymore and the screen is blank. Pressing the last switch on the right lights up some LEDs but nothing else happens.

What should I do? I tried desoldering the LCD but I can’t seem to do it.

I also did another mistake, I clipped the headers of both the controller board, and the in-between headers (between the filter and the controller) and now they are too short. However that mistake was before the LCD and it worked. I need to buy a replacement header however :frowning:


The errors you experience may still be of some coincidence. Buy some new headers, desolder the old too short headers and solder the new ones. Do not rely on that they are not the problem. Staying in line with the building procedure keeps you in line with the causality of the troubleshooting order…

Ok, I need to buy some new headers tomorrow (if I can find them) and check if that fixes the problem.

The good thing is I don’t need to desolder anything since they are the headers between the two boards, the ones that are stacked on top of the soldered headers of the filter board.

Thanks nightworxx!

Maybe some of the solder joints under the LCD are shorting joints/traces on the LCD board?

I clipped everything as short as I could before I soldered the LCD but that could be the problem too.

The thing is I can’t desolder the LCD to test. I only have desoldering wick, maybe I need a pump?

Does it sound more like a shorting problem than a header problem?

If the +5V and GND connections to the filter board are solid, the control board should work.

I did a little bit more troubleshooting.

I was applying 7.5 volts before. I applied 9 volts and now LED’s 3 and 7 started flashing. After adjusting the LCD contrast with the trimmer I saw text on the screen. The text “muta” is flashing most of the times, sometimes the text “mutao” appears also. The encoder has some effect some of the times but the switches don’t do much.

Measuring the voltages at the point where the filter and the control board are connected I get 4.15 volts.

The solder joints under the LCD seem to be short enough with no connections with the screen apart from the screen’s ‘legs’.

If you remove the control board, do you still get 4.15V?

This seems to point to a bad power supply - do you know how much current your 9V supply is delivering?

I removed the control board, added some male/male headers to the female headers of the filter board (so I can measure) and I got 4.99 volts.

The power supply is variable volts up to 1 amp. It’s new, I bought it yesterday, and I don’t have another to test with.

So either something causes a short on the control board (which resistance do you measure between GND and +5V when the control board is unplugged?), or your power supply is failing to deliver the required current (do you have any datasheet/documentation you could link to?)

I get 1.4K resistance between GND and +5V on the control board.

Unfortunately there is no datasheet I can point you to for the power supply.

It was the $&^*^#*() power supply! I used the power supply from my Waldorf Blofeld which is 12V 300A. All the display problems have gone away, the LEDs, switches, encoders and pots work great.

BUT… I have to turn my audio interface channel all the way up just to hear a extremely faint sound. Midi works as I can see the note appear on the screen but the machine barely makes a sound.

Should I open a new thread for this problem?


Very first thing to check is that the -5V rail on your filter board is there. The Blofeld PSU, if it’s actually higher than 12V, might have killed the LT1054.

At the end of the SMR4mkII assembly instructions you’ll see several test points on the filter board. On which ones do you have signal? Also: have you soldered the jumpers near the input/output jacks?

I think I’m going to wait until I get a new power supply before making the measurements you asked for. I don’t want to make any more mistakes now that I’m so close.

Should I get a 7.5V one or 9V?

By the way, thanks a lot for your help. Although it’s Sunday your support is fantastic!

I’m going to order some LT1054 chips to have them in stock just in case. Could you check which one of these is the correct one please?

What other chip could be burned by a possible overvoltage? Since I’ll make my order anyway I’d like to have some in stock (also thinking of building another different Shruthi filter in the future)

Mouser 595-LT1054IP is fine. That’s the only part that could have suffered from overvoltage.

Great, thanks!

Found the problem! I checked the voltages and everything was as supposed to be so I started examining the filter board for obvious mistakes. Wait a minute, are the pads next to the input and output pots supposed to be left empty? Duh! I forgot to bridge them.

Now I have to tune the filter and check that MIDI works but that can wait until tomorrow.

It sounds great though!