Finished Build: No Cymbal, weak Handclap

Discuss Yocto construction and related issues
  • I remeasured the voltages for the Cymbal and Handclap ICs. I was fairly certain the voltages were correct while building the instrument sections but that doesn't look to be the case now.

    Cymbal:

    U5: 13.86v, -13.81v
    U3: 14.5v, -14.6

    Handclap:

    U23: -14v
    U22: 14.7v, -14v
  • Hi there,

    the VCA and waveshaper of your clap seems not to work properly.
    check with a scope the shape you have on U23 Pin13

    Have a look on the TR-808 service manual page 6. Everything are explain on how works the clap.

    Parts number of the Yocto v1.0 is corresponding TR-808
    Best regards,
    e-licktronic
  • Hi Vincent,

    Seems like AN6912 needs to be replaced? Here's a scope screenshot of U23, pin13. Voltages are off at the output despite -14v on pin 12 and the waveform is also missing the last three peaks after the initial peak, as shown in the service manual.

    https://imgur.com/a/ehAhnTQ

    Regarding the Cymbal, it is now fixed. A transistor pin was shorted to ground due to how close it sits next to one of the potentiometers. It was making contact but after bending it out of the way, the output is crystal clear now and sounds great!
  • I just replaced the AN6912 with an LM339N and I still have the exact same clap problem. I guess I can rule out AN6912 being faulty. Sucks since I had to trash it in order to replace it...
  • the_sauce wrote:Hi Vincent,

    Seems like AN6912 needs to be replaced? Here's a scope screenshot of U23, pin13. Voltages are off at the output despite -14v on pin 12 and the waveform is also missing the last three peaks after the initial peak, as shown in the service manual.

    https://imgur.com/a/ehAhnTQ

    Regarding the Cymbal, it is now fixed. A transistor pin was shorted to ground due to how close it sits next to one of the potentiometers. It was making contact but after bending it out of the way, the output is crystal clear now and sounds great!
    What do the other key handclap signals look like? Take a look at figure 13 in the original 808 service manual and compare your readings to what's given there. You will have to take multiple readings to get a complete picture. That circuit is fairly complex, so a lot can go wrong there.
  • Hi helectromagneticus,

    A bit late since I had to return the scope and wait until I could borrow it again.

    I managed to take readings of all but Pin 8 of BA6110 since the service manual shows an audio waveform for comparison. I didn't find a way to inspect that with the tools I have available. Happy to try if anyone has suggestions on how to do that.

    https://imgur.com/a/0ke85PI

    To be honest, I don't know how to interpret these readings in order to troubleshoot. The only things I can tell are some of the readings are off in terms of the signal shape and all readings are off in terms of voltage. None of them go from -15V to 0. You can see the relevant measurements in the bottom left of each screenshot.

    Also, note IC23 is now an LM339N, not an AN6912.

    Does anyone know what I should be looking at next?
  • the_sauce wrote:Hi helectromagneticus,

    A bit late since I had to return the scope and wait until I could borrow it again.

    I managed to take readings of all but Pin 8 of BA6110 since the service manual shows an audio waveform for comparison. I didn't find a way to inspect that with the tools I have available. Happy to try if anyone has suggestions on how to do that.

    https://imgur.com/a/0ke85PI

    To be honest, I don't know how to interpret these readings in order to troubleshoot. The only things I can tell are some of the readings are off in terms of the signal shape and all readings are off in terms of voltage. None of them go from -15V to 0. You can see the relevant measurements in the bottom left of each screenshot.

    Also, note IC23 is now an LM339N, not an AN6912.

    Does anyone know what I should be looking at next?
    The timing looks good for the clap triggers, but the voltages are not correct as you've pointed out. What is the voltage on pin 12 and pin 3 of IC23? Pin 3 should be at ground and pin 12 should be around -15V. Check also the connections for Q73, Q72, and Q71. Q73 is in the feedback loop for the clap envelope generator and so perhaps there is a problem with it for you.

    Does the maracas section work?

    I suspect you have a soldering problem considering that was the problem you had with your cymbal circuit.
  • helectromagneticus wrote:
    the_sauce wrote:Hi helectromagneticus,

    A bit late since I had to return the scope and wait until I could borrow it again.

    I managed to take readings of all but Pin 8 of BA6110 since the service manual shows an audio waveform for comparison. I didn't find a way to inspect that with the tools I have available. Happy to try if anyone has suggestions on how to do that.

    https://imgur.com/a/0ke85PI

    To be honest, I don't know how to interpret these readings in order to troubleshoot. The only things I can tell are some of the readings are off in terms of the signal shape and all readings are off in terms of voltage. None of them go from -15V to 0. You can see the relevant measurements in the bottom left of each screenshot.

    Also, note IC23 is now an LM339N, not an AN6912.

    Does anyone know what I should be looking at next?
    The timing looks good for the clap triggers, but the voltages are not correct as you've pointed out. What is the voltage on pin 12 and pin 3 of IC23? Pin 3 should be at ground and pin 12 should be around -15V. Check also the connections for Q73, Q72, and Q71. Q73 is in the feedback loop for the clap envelope generator and so perhaps there is a problem with it for you.

    Does the maracas section work?

    I suspect you have a soldering problem considering that was the problem you had with your cymbal circuit.
    Hi again,

    Thanks a lot for your reply.

    Pin 3 is at ground, pin 12 is -14v, just outside the +/- 5% mentioned in the build guide. The maracas are ok. I checked the connections for Q71, Q72 and Q73. They look all right and nothing appears to be shorted but I reflowed the joints again just in case. Still the same problem.

    Could it be that one of these transistors is somehow faulty? If there's a chance of that, I could try ordering a few more and swap them out.
  • Hmm, without having your unit in front of me it is difficult to determine what the problem is. I would proceed with the following:
    • Check the orientation of your transistors and verify their pinouts against their datasheets
    • Check the orientation of IC23
    • Verify the connections in each circuit node by following the schematic. For example, check that R371 is connected to GND and the base of Q72 etc. This is a painstaking process but if you are thorough you can be sure that everything is wired up right.
    • Verify resistor values
    • Check the orientation of C144 and read the discussion about this part in the forum
    I wish I could help you more, but it's quite hard to troubleshoot remotely...