Troubleshooting and known issues

This page contains some tips to help you identify problems in the assembly of your Shruthi-1, or recognize known hardware/software issues.

Digital board troubleshooting.

It looks like I don’t have the right EEPROM chip.

Atmel eeproms are strangely labelled. if it has 8 pins, comes with your kit, and starts by “AT”, it is the eeprom :)

The Shruthi-1 seems to boot correctly (LEDs 3 and 7 are lit) but after having soldered the display it does not show any text.

If the display shows a filled line (16 7x5 filled squares) and an empty line: there’s a communication problem between the LCD module and the MCU. One of the LCD module pins is not correctly soldered or is shorted with its neighbor. In last resort check the continuity between the pins of the MCU that are connected to the LCD. If you observe shorts between some of those pins, it’s likely that the AVR has been damaged by an electrostatic discharge.

If the display shows 2 filled lines: the contrast is set to its maximum value, in the wrong direction. Turn the R21 trimmer by about 5 turns (you’ll notice it if you turn it in the wrong direction – you’ll have reached the end of the trimmer and a slight click will be heard at each turn).

If the display shows nothing: the contrast is set to an incorrect value. Try adjusting the R21 trimmer until you see the text or the filled line. Check for bad joint in the contrast trimpot – in particular check that the GND pin is correctly soldered. Grounded points are more difficult to solder due to the ground-plane absorbing the heat.

Remember that even if the MCU is dead, blank, or removed from its socket, the LCD module will show a filled line. If you don’t see the filled line or the splash screen, there’s a problem with the contrast setting.

MIDI doesn’t work.

When a MIDI note arrives in the Shruthi, it shows a note icon in a corner of the screen. If MIDI doesn’t work, check that the optocoupler is correctly inserted in its socket. Also, check that you haven’t swapped the EEPROM and the optocoupler.

The parameter values seem to be “flickering” – as if the pots were constantly tweaked by an invisible hand.

Your power supply is not providing enough current, and this cause oscillations on the +5V rail. Try a different power supply (300mA should be fine but I have seen some supplies labelled 300mA having trouble delivering currents as low as 200mA).

Software troubleshooting.

The MIDI update procedures does not complete.

  • This might be related to the software tool you use to upload the .mid file. Many SysEx management tools strip the timing information of the .mid file, concatenate all the SysEx data blocks, and send the resulting data stream using their own clock and blocking algorithm. For the firmware update procedure to work correctly, data blocks must be spaced by at least 250ms to give enough time for the Shruthi to reprogram its flash memory. Adjust the speed setting of your SysEx tool accordingly, or use a plain sequencer to play the MIDI update file. For firmware update we recommend the use of Elektron’s C6 SysEx tool, configured with a 250ms delay on Windows and 15 ticks delay on OS X.
  • The M-Audio Firewire 410 has a bug which causes the duplication of some bytes in the MIDI stream. Here is an example of report of this problem. Please report the problem to M-Audio and try another MIDI interface. Cheap USB/MIDI cables have been successfully used to do firmware updates.

A weird LED pattern is displayed during the MIDI update procedure.

If the x-x-x-x- LED pattern stays on during the MIDI update, with LED1 and LED2 occasionally blinking, this means that some unexpected, non-SysEx messages are present in the MIDI stream (this could also be SysEx for another product/system). While such messages might not hamper the progress of the MIDI update procedure, they indicate that there’s something unusual in your MIDI setup (such as the presence of another MIDI source in the chain) worth investigating…

SMR-4 / SMR-4 mkII board troubleshooting.

There is no sound.

Check that a jumper is inserted in the 4 poles or 2 poles position of the poles selector.

I have connected an external audio source but I can’t hear it

The SMR-4 board has a VCA, which needs to be opened to let the filtered audio signal go out. You need to either:

  1. Hold a note (for example, hold S1 to trigger a test note – and set the two oscillators to none if they are bothering you)
  2. Disconnect the envelope 2 from the VCA in the modulation matrix, by setting to 0 the modulation amount of en2 to vca (9th entry in the modulation matrix for most patches).

The patches 125-128 are good examples of how to setup the Shruthi-1 for external signals processing.

The volume potentiometer does nothing.

The 3 terminals of the potentiometer must be soldered to the PCB – in the schematics it is used as a voltage divider, not a plain variable resistor.

The output signal sounds ring-modulated or there’s some buzzing/humming on the output.

The “ring-modulated” sound is due to the DC adapter/supply not generating enough current. This can be verified easily by observing the +5V rail on a scope – if you see some periodic drops, something is wrong with the supply. We recommend a 300mA or 400mA supply if you stick to the parts used in the kit, and a 500mA in the event you have soldered a high-brightness LCD module different from those shipped with the kits (such as those sold by CrystalFontz).

Another symptom of a poor quality DC adapter is the presence of low-frequency hissing/humming in the output.

The only sound I can hear is a loud plop/buzz.

Check for swapped resistors values, in particular in the red&black gang (220, 10k, 220k, 2.0k, 2.2k…). Swapping two of those resistors can drive the gain to 1000x its normal value, or push a +5V DC to the signal that will crash it to the op-amp rails.

Check that you haven’t swapped the 68 and 68k resistor in the output amp section.

I get no sound or a a distorted sound. How do I know at which stage the problem is located?

You can “probe” the circuit with an audio jack connected to a mixer/amp. The tip of the audio jack should be connected to the point you want to probe ; the sleeve should be connected to any point of the ground at ground potential (points marked “GND”).

On the SMR4mkII, the audio path is the following:

You should hear:

  1. Raw audio signals
  2. Raw audio signal with a 0.33 gain + audio input
  3. Audio signal filtered by 1 pole
  4. Audio signal filtered by 2 poles
  5. Audio signal filtered by 3 poles
  6. Audio signal filtered by 4 poles
  7. Audio signal filtered by 2 poles or 4 poles depending on the position of the Poles selector
  8. Filtered audio signal, with VCA applied to it
  9. Final audio signal

Look for cold solder joints, swapped parts in the area around the point where the signal chain breaks.

On the SMR4, the audio path is the following:

You should hear:

  1. Raw audio signals
  2. Raw audio signal with a 0.33 gain + audio input
  3. Audio signal filtered by 1 pole
  4. Audio signal filtered by 2 poles
  5. Audio signal filtered by 3 poles
  6. Audio signal filtered by 4 poles
  7. Filtered audio signal, with VCA applied to it
  8. Final audio signal

Look for cold solder joints, swapped parts in the area around the point where the signal chain breaks.