POwer test of 4Pole Mission
  • Good morning !!!

    I think i have a problem on my shruti 4 PM filter board.
    I have just finished solder, and at the red - blue- green point,
    i have +3V and -3V everywhere !!

    Have you got an idea ?
  • With a photo !!

  • Which power supply are you using? What is the voltage at the SW “bridge” near the power connector?

  • It's a 9V power supply, and i have 5.80V at SW bridge.
    POwer supply delivered 8.96V
  • I'm at work, i can't response immediately.

    Thx olivier for your help
  • Looks like your power supply is too weak – I think the 8.96V you have measured is without load, right? As soon as you connect it to a circuit, the voltage drops to 5.8V and this is not enough for the regulators. Try another one.

  • Yet it is the same that works with the smr4 mkII !!!!
    I don't understand.
    I have a selector on the power supply, can i increase to 12V ?
  • Yes, 8.96V directly at the power supply
  • I have 8.94V between SW bridge point un ground point on the eight point connector
  • So at which point do you get 5.8V?

    What are the voltages on the I / O / (-) pins of the 7805 and I / O / (+) pins of the 7905?

  • [URL=http://imageshack.us/photo/my-images/651/shruthi4pm.jpg/][IMG]http://img651.imageshack.us/img651/3337/shruthi4pm.jpg[/IMG][/URL]
  • Sorry i have 0V between this two point

  • To imbed images use exclamation points around the hyperlink like ! http://... ! but omit the spaces.

    I think you’re measuring the voltage at the two electrolytic capacitors in front of the voltage regulators…

  • Hmmm, this is not really what I asked…

    What are the voltages on the I / O / (-) pins of the 7805 and I / O / (+) pins of the 7905?

  • !http://imageshack.us/photo/my-images/651/shruthi4pms.jpg/!
    it's not these point ?

    (I have a problem with image)
  • like this:


    edit: not sure, if imageshack allowes to ebedd images this way.

  • Voltage regulator:

  • Yes titus, between - of IC11 and + of IC12 !!!and i have 0V
    It's not that ?
  • olaaa, it's not the same !!!!

    I think I've found. I reversed the two Voltage regulator.
  • I am awfully sorry My mistake is resolved.
    I have +5V and -4.99V
  • Well done solving the problem. I'd consider replacing the regulators eventually as being reverse biassed can shorten their life (found that out from my Oberheim Cyclone that had no reverse voltage protection for plugpacks!)
  • You advice me to replace them ? if I understand
  • They cost very little, so for peace of mind it can be worth it.

  • Argh! I am also having power test problems now. I’m using a 12-volt power supply, 500ma, that’s putting out 17v at SW. The readings at the indicated coloured dots, with the LT1054 (IC7) in are minimal, .06v, and are reversed polarity. I checked the polarity of the polarized caps and they seem to be in the right place, and I assumed the long lead of the 4.7u caps was positive. The regulators are installed with the heatsinks facing the outside of the PCB.

    Any ideas? Someday, maybe when I do my 20th Shruthi, I’ll actually get one to work first time.


  • 17v might be to much. LT1054 datasheet says “Operating Range: 3.5V to 15V”

    i have no idea what happens at > 15v, but i figure using another psu with like 7,5 – 12v might be something to try

  • Looks like you have fried the LT1054.

  • Always be cautious with supplying power. Too little is better than too much. With too little it just won’t switch on.

  • I may have fried the chip. Is there a way to test it?

    The first power supply I tried, also rated at 12V put out nearly 20V! I’ll see if I can find another LT1054.


  • If you don’t get minus the input voltage on pin 5 of the LT1054 it’s dead. This seems consistent with your observations. The LT1054 is not designed to handle voltages above 15V so there’s not much hope here…

  • At least I’ve learned to ignore whatever is written on the wallwarts and test them first.


  • It’s not just about testing them. But realising that a good many of them put out a higher voltage when they are unloaded. Or will put out a higher voltage when their amperage rating is far in excess of what the Shruthi actually needs, as they are not loaded enough for the voltage to settle down to where it should be.
    In my experience, switchable wallwarts are often crappy about putting out what they are supposed to be putting out too.

    I guess a regulated wallwart would help, but there isn’t really much need. Suitable, unregulated ones are cheap and generally easy to get hold of.
    I don’t think the Shruthi requires more than 300ma(??). I have 9v 500ma and 660ma ones from RS and Farnell and they have been fine with all my Shruthi’s so far.

  • The Shruthi doesn’t need more than 150mA. The problem is that it’s common to see wallwarts rated 300mA fail to deliver the 150 or 160 the Shruthi needs :/

  • Godlyke Powerall and be done with it! It makes all my Shruths work (at the same time). MidiPal too.

  • I picked up another (well, a pair, just in case) LT1054 and tested with the power supply I’m using for the other Shruthi, same result. Minimal power getting through to anything.

    I checked all of the caps again and they seem to be oriented correctly. The only thing I’m not sure of is the orientation of the 4.5u caps that Olivier provides with the kit. As I mentioned, I assumed the long lead was positive, but I can’t see any markings on those caps that would let me check the orientation after-the-fact.

    So, I’m back to looking for ideas.


  • These caps are not polarized, so no worry here.

    Do you have a short between ground and one of the +5V or -5V rails?

    Which voltage do you get at pin 5 of the LT1054?

  • I used pin 3 as ground and I’m getting +0.2v at pin 5. All of the red points on the photo are getting +0.4v and all of the blue are +0.3v.

    I checked continuity between all of the green, red and blue points and everything seems okay. The odd one has the meter “hunting” a bit but it settles down to 1 quickly.


  • What are the voltages on both sides of D1?

  • Depends on which probe I use. I have 15.3 at SW, then if I leave the + on SW, I get 15 on both sides of D1. If I leave the – on SW, I get essentially nothing on both sides.

  • When measuring a voltage the (-) should always be put on a ground point ; and the (+) on the point you want to measure the voltage at. Otherwise you are measuring voltage differences.

  • What is the best point to get a ground?

  • The hole on the header marked GND.

  • Smartass! Good point ‘though! Following Titus’ suggestion, I get the same results, 0 on one side of the diode and .4 on the other.

  • Didn’t mean to be a smartass. It took me a while to realize that once the board is powered, all the voltage and ground points are active/connected by the PCB traces. I mean this is really a “duh” moment, but it wasn’t obvious to me from the start.

  • It’s okay to be a smartass when you’re right. I appreciated the advice, just giving you a bit of a hard time, hope you don’t mind. I’m wondering if I’ve screwed up D1?

  • I think maybe. You should definitely have voltage on the other side of it. ~9V I think…

    I’m still studying this stuff, but I believe the stuff near the regulators steps the voltage down to 5 and then splits it into -/+.

  • This is strange, one side of the diode should be at the same voltage as your power supply…

  • A protection diode prevents the wrong polarity voltage from going through it and damaging the circuits behind it right? So what happens if the diode burns out? Does it stop passing voltage or pass inconsistent voltages?

  • The power supply flow is the following:

    • Arrives at the connector.
    • The circuit is eventually opened / closed by a switch if you solder it at the SW switch (it’s kept close if you solder a jumper here).
    • When the polarity is wrong, D1 blocks the current. Otherwise it just causes a small voltage drop (a few tenths of volt) across it.
    • Then the input voltage is sent to the LT1054 and the few caps around it – and a negative voltage is generated from it (if the input is 10V, the output, on pin 5 of the LT1054 will be -10V).
    • The the 7805 (7905), brings the 10V (-10V) to 5V (-5V). Excess power (input voltage – 5V times consumed current) is dissipated as heat.

  • The diode doesn’t burn out unless you apply very high voltages to it. If you plug the power supply with the wrong polarity it’ll just block the current, but it won’t be damaged…

  • Thanks pichenettes!

  • I see what you mean. One side should always be input voltage. Has to be. This points to a problem upstream then, to SW, the connector, or the PSU. Right?

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