midipal is dead after assembling
  • Dear all,

    just finished assembling the midipal.
    Unfortunately it shows no signs of life. LEDs dead when connecting Midi In and Out, display also dead.
    I have measured 3.3 volt at the points described in the assembling instructions but this is all I can do.
    Is there a step by step trouble shooting way in order to check the parts and soldering points?
    I believe my soldering skills are not that bad but I have no knowlede in microelectronics, so I do not know how to find the mistake in the built.
    I would be grateful if somebody could help.

  • Was it a kit with a pre-programmed chip?

  • I guess so, I only have purchased it 2 weeks ago.

  • Unfortunately, a good way of knowing if the chip is alive is to try talking to it with an AVR programmer. I assume you don’t have one?

  • Never heard of AVR Programmer, is that a computer program?
    I thought all chips sent out after a certain date would be already programmed?
    Is the AVR case very difficult for am dummy?

  • The AVR programmer is an USB device to talk to an AVR chip – for reading its memory, or flashing programs onto it. The chip in your kit is programmed ; but to help you identify your problem we need to know if the chip is alive or not ; and to do that, the best way is to try to talk to it with an AVR programmer.

  • just in case, vincent, could you send a photo of your assembled board?

  • I will make a picture and post it, so you can have a look.
    One thing I forgot to mention: I destroyed the encoder by soldering it to the wrong side of the board (don´t ask why i did this!).
    I have replaced it with the the following item, to me it is excactly the same as the original one, but maby this is not the case?


  • Encoder shouldn’t be a cause of the problem you describe. At the very worst you can get inverted rotation or click / rotation swaps with some encoders with different pinouts ; but shouldn’t explain a MCU that doesn’t boot or an unresponsive MIDI interface.

  • One thing: if you turn the contrast trimmer to one of its extreme positions, do you get filled squares on the LCD?

  • Yes, the sqares are filled.

  • Ok… Then it means that the most likely cause of the problem is that the processor just doesn’t boot. Check the soldering of the crystal, check for shorts between adjacent pins of the MCU.

  • That is good news! I will check the soldering points. Hopefully this helps.
    I attach a picture so you can have look at my work.

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  • Check the lower pins on the right side of IC2. The third one from the bottom looks a bit funky, maybe it’s just the picture.

  • Damn! Checked the IC2 again and found some shorts! When assembling I did not find them, strange.
    I have a meter set to buzzer mode which I use for checking the pins. Is that the right way?
    I guess there are no internal connection in the IC that make the buzzer beep? Power is not attached.
    Please see below a picture of the infected pins.
    How can I access the upper ones, the display is in the way. Is it possible to remove the display without destroying it?

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  • How about getting a solder wick in between the display and the CPU and gently trying to remove some of the excess solder?

    Some pins could be the same, at least on a very large IC package. You would have to check the data sheet to be sure. However, let’s assume that’s not the case here for this small CPU.

  • it will be pretty tricky not to destroy the display trying to remove it. You better try with the display in place.
    Put some flux in here and use solder wick, this should be enough.

  • Ouch. The two pins on the bottom left are for the crystal – with them shorted the MCU cannot boot. To confirm – because sometimes it’s hard to probe the tiny pins of the MCU – check that there is no short between the left and right pads of the crystal.

    The pins on the top left of the MCU are the LCD enable pin and the MIDI in/out respectively. Shorting them will cause serious problems on both the display and MIDI transmission.

  • had it partially running! but no display backlight. showed the monitor app and registred incoming notes.
    after 10 sec it broke down again. now completely dead again. I think that on ethe pads (below pin 3 from bottom left) has lost contact to the board because of too much too hot soldering iron penetration.

    is this the end of the story?

  • Nope! Just hit it (carefully) with another drop of solder. Don’t overheat it, don’t make a cold solder joint. If that doesn’t help, let’s find the trace where it leads to and carefully solder a thin wire to there.

  • what temperature do you recommend for soldering this kind of thing?

    thank you all for your help so far.
    anyway, I will get a thinner solder iron tip tomorrow and continue working on the thing.
    have a nice evening!

  • For repairs try a High Power computer controlled Iron with low temperature, so you can be shure it holds the low temperature no matter what/how long you touch with it. I work at 300° – but i have a rather good 60W Soldering Station….

  • For smd works, 30w is fine. Using flux is pretty vital there.

  • I think pin 19 an 20 could be shorted as well. You should see my FrankenPal after replacing the whole MCU (the first was dead, still don’t know why) without hot air smd rework tool, there are I wires… With time, a good soldering station, a good wick and good flux one can do amazing things. ;-)

  • I found the most important thing was to use no pressure at all on the MCU legs. Just the weight of the iron. Let it gently drift across the legs drawing in the solder as you go. After a couple of passes, you should have clear solder joints.

    If you press on them, they buckle and come away from the pads, and that causes more troubles. Low heat, no pressure, lots of flux from a flux pen. Thin solder too!

    I should add that I have spent so much time and used so much solder wick on this vector board/perf board project of mine. I don’t even want to talk about it. But I think there is a special place set aside for people who perservere through projects like this. Don’t give up!

  • First-thanks to all of you for your help and motivation.
    I got a new iron tip, lots of solder wick and flux to fix the shorts at the CPU.
    I cleared most of them but remain with a very strange one, see photo.
    Strange thing, there must be something behind or under the pins??
    Anybody go an idea?

    I got the device running for some 30 seconds, but backlight is dead.
    Than it crashed again and was dead again.

    I doubt very much that I get this thing properly running in the end, anyway thanks for help.

    final try.jpg
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  • Both pins are ground pins of the MCU so it’s normal that they are “shorted”. MCU in square packages like that often have power and ground pins duplicated on each side!

  • finally-a clear end in the end! smoke signals out of the CPU.
    I would say: that was it! we can close the issue.
    I think I was not patient enough when I first soldered the CPU-but to be honest, this is not easy.

    Any chance to get a new kit without case for reduced price for a second try?

    Best regards!

    smoke signals.jpg
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  • not as bad as in the video!
    checked voltage: 3,3 V on the measure points, 9V at power supply.

  • With the availability of the assembled units next week, I won’t do any more kits of the MIDIpal.

  • Probably a good idea to switch to assembled kits. At least for soldering heroes like me!
    Please contact me when you are ready to send out the ready made midipals.

    Best regards.

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