Missing VCO on fresh Anushri build
  • Hello!

    I just completed my Anushri kit. I started it up to test it out, and I found that I have no VCO coming out of the output jack. Seemingly everything else is working. The DCO comes through just fine in the DCO setting, but not as the sub octaves. Using the DCO, I can test the filter, and it seems that everything is fine there. I’ve also played with the drum machine and that seems to be working fine also. The LED in the drum setting doesn’t light up, but I imagine that is just a bad solder joint. I think that the VCF LFO knob changes the intensity of the drum pattern in drum mode, but it also seems to change the VCF LFO setting at the same time for the DCO. MIDI in and sound output are working fine, except for the primary oscillator’s absence.

    All of the 5v, -5v, 4.1v, and -4.1v spots are at the correct voltage. The grounds are all also grounded. In the power section debugging, I get
    1) 14.3v
    2) 13.5v
    3)-12v

    It seems that my 12v power supply is a bit higher than 12 volts here.

    In the VCO test section, I get
    A) 1.8v – 2.4v
    B) 2.6v – 2.7v
    C) 2.8v – 3v
    E) -4.9, moving lower slightly and then back
    F) 0v – 3.29v
    G) 4.11v
    H) 3.97v
    K) -2.48v
    U) 2.46v
    V) .44v

    I skipped over anything that didn’t seem to deal with the VCO specifically. Is there anything here that jumps out at anyone as something wrong? I will probably have to spend some time going over my solder joints, but is there a specific place I should be looking for mistakes? Is there any additional information I can provide?

  • > Is there any additional information I can provide?

    Yes:

    • On the test point A, you report 1.8V – 2.4V ; but how does it change in function of the key you press? Does it correctly jump by 0.5V every octave?
    • Test points E, F, G, H are not meant to be verified with a multimeter (the voltage at this point changes, so a multi-meter does not see and measure that). They should be measured with an oscilloscope, or at least with an audio interface. Could you report what you see there?

    Could you also post photos of your boards (both sides)?

  • Point A did change based on the note at around .5v per octave. As for E, F, G, and H, I hooked them up to an audio probe I made a while back out of half a 1/4” TRS cable, an alligator clip connected to the ground, and a capacitor connected to the signal part. I tested the probe on the output jack, and I was able to get audio from the output jack. I then checked those other 4 places. I heard nothing at all, but just to be certain, I recorded a little bit to see if there was anything I was missing. There was nothing but a little bit of noise. E, F, G, and H were silent.

    I took some photos of the boards as you requested, and they are attached. Let me know if there’s anything you can’t see, or if you need a clearer shot of anything.

    Thanks for taking the time to look at all of this.

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  • I would trim all the excess leads to start (just to rule out any shorts) It also looks like you forgot to solder one of the VCO trimmers.

  • Redo all your solder joints. All of them.

    Looks like you did not use enough solder and I can see many, many pins (especially on ICs) in which there is no electrical connection.

  • Do take the ICs out of their sockets first, to be on the safe side.

  • I took your advice and I spent some time redoing the solder joints. I think the pictures make the joints look worse than they were. I did take out all of the ICs beforehand. I also went through and I shortened the leads that were too long. In the process, I think that I may have made a rather serious mistake, though. If you look carefully at the traces in the board just above where LED 4 attaches (on the underside), you can see that I may have actually dug the trace out while I was clipping a lead. These traces appear to attach to knobs 5 and 6 (the middle pin of each). I don’t know where they attach on the other board. I tried to flow a bit of solder to reconnect the severed pieces, but I do not think that I was successful. I think that is the only error that I can see now on the boards, but I could be wrong.

    I plugged the device in again and tested it out. It still receives MIDI signals, and it still outputs sound, and I think I may have the primary oscillator coming through now. But the device does not seem to be working correctly by far. The VCF has to be in the high pass mode to pass sound at all (the other two modes are silent). The fuzz switch kills the sound when set to ON. The LFO seems to be set to some sort of sample/hold setting. None of the LEDs except for LED 4 turn on at all when I set the device down. LED 3 did turn on when I lifted the device, but LED 1 and LED 2 never turned on, even when switching modes. I really can’t tell if the mode switches actually switched anything as most of the knobs were unresponsive. The drum machine would not engage this time when I pressed the run/stop button.

    So in some ways I improved things, in others I did not. I am hoping that the broken traces explain all of these problems and I can run a couple of jumper wires to solve the problem (please let me know where). I apologize for making a Frankenstein of the elegant design. Let me know if there is any more information that I can provide to help diagnose the problem.

    Thanks again for helping me out.

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  • Look at the schematics or board image and use a multimeter in continuity testing mode to see if the traces are really damage. From your picture it looks like only the soldermask has gone, so they are probably still functional.

    As for the other problems… go through the signal chain as explained in the end of the assembly instructions. Check the VCO output, then the filter output etc to identify which parts of the circuit are working/non working. Trying to diagnose the problem just by listening at the final output signal is not the way to go…

  • I went through the debugging steps once again. All of the voltages were in the right places.

    At point E, I alternately heard a tapping sound, a reversed sawtooth wave, and for a brief time a regular sawtooth wave. I was providing no MIDI input at this point. The variation in the sounds seemed to come from the position of the boards in space, and on further inspection, it seemed to have to do with the wiring for the MIDI jacks. I took everything apart, re-soldered the wires of the MIDI jacks, check continuity between each prong at the jack and at the board, and determined everything to be okay there. I really can’t say why this happens. Does this make any sense to you? Point F was the same but louder. Both of the pictures were taken from F.

    As I was checking the voltages, the LT1054 began to arc, and then smoke, and now the case is cracked, so I’m fairly certain it’s dead. The data sheet says that it should have no problem handling up to 15v. Where is the best place to purchase a single replacement?

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  • > The variation in the sounds seemed to come from the position of the boards in space

    This indicates a bad solder joint somewhere – or maybe a pin that got bent when a chip was pushed in the socket.

    > The data sheet says that it should have no problem handling up to 15v

    Could also have been due by an excess current consumption, for example if the -5V rail got shorted.

    > Where is the best place to purchase a single replacement?

    The best way to get an answer is to say where you live, since shipping fees/delivery times will vary.

  • I’m in Arizona, in the US.

  • Okay, after waiting a little while for the parts and also for getting my nerve up, I traced the entire circuit with my multimiter to see if there was any break. I tested both boards individually and found only one disconnect for an LED, so I decided to put them together and check if the J sections were connected. I had a sneaking suspicion that they were not. I think that I must have soldered the pin parts in backwards, thinking that the pins would be too long the other way. I was able to heat each pin long enough to melt the plastic and push it deeper into the sockets on the other board, and, while inelegant, everything seems to be working fine now. It’s a wonderful device. I think a note in the instructions about which way those pins go would be really helpful. I’ve done a lot of electronics projects before, but I’ve never encountered that piece.

    Thanks, again.

  • Wow, can’t believe I did not notice that on the pictures you had posted :/ I was too busy checking resistor colors :(

  • Pfew, that was a long road to a working machine, but good to hear to persevered and got it working in the end !

    The problem is always somewhere you do not expect it …

    As for the LT1054, Mouser, or even ebay, like here (US source)

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