Absolute voltage on 7905 and 7805 is different (8.33V and -2.08V)
  • Hi!

    I’ve just finished building my Anushri and got a problem.
    LEDs is ok, buttons is ok, but there is no sound. If I turn my amp very loud and play MIDI on my keyboard then I hear very weak sounds. Its like a square, distorted sound. It doesn’t change when I touch knobs.

    So, I started to check power distribution and find error right away.
    Absolute voltage on 7905 and 7805 is different (8.33V and -2.08V).
    All red points have +4.95.
    Voltage on all green points are +0.78!
    Purple are +4.08.
    Cyan is 0.58!

    Could you help me please?

  • If by absolute voltage you mean input voltage… it looks like the LT1054 is not operating correctly. Do you get -2.08V on its pin 5? If so:

    • Check that you have not exposed the LT1054 to an input voltage exceeding 15V.
    • Check that all caps around the LT1054 are correctly oriented.
    • Check that your PSU can deliver at least 300mA (or better: 500mA).

    There might also be a short between the -5V rail and ground, causing an excessive current draw… What is the resistance (with everything powered off) you measure between a -5V point and ground?

  • pin 5? Is it number 3 on this scheme – http://www.flickr.com/photos/mutableinstruments/7711692322/sizes/h/in/photostream/ ?
    Yes, -2.08V on that pin.

    1) Check that you have not exposed the LT1054 to an input voltage exceeding 15V.
    Do you mean number 2 on the scheme?
    8.33V on that pin.

    2) Check that all caps around the LT1054 are correctly oriented.
    Double checked. Looks OK.

    3) Check that your PSU can deliver at least 300mA (or better: 500mA).
    I tried two different PSU: 330mA and 1700mA.
    Big one shows the same voltage on pins as small one.

    4) What is the resistance (with everything powered off) you measure between a -5V point and ground?

    Resistance on 7905’s -5v point is 539.
    Its no good, right?

  • yep it’s test point 3.
    1) it’s what comes out of your external power supply. shouldn’t be more than 15V as that’s to much for the 1054

  • 1) no, there is only 9v.

  • What is about resistance?
    4) What is the resistance (with everything powered off) you measure between a -5V point and ground?

    Resistance on 7905’s -5v point is 539.
    Its no good, right?

  • sorry i can’t measure today, i don’t have mine at home.

  • What’s about today? =)

  • caveman test: How hot is the 7905? (touch it)

  • Hot. Can’t hold it more than 1-2 seconds

  • I agree with altitude, cave man test seldom lie.

  • Yes, it is hot. But what does it mean?

  • It menas it delivers to much current – theres a short somewhere. The 7905 only has to power some OP Amps with some mAs so it shouldnt get hot at all.

  • Sorry, I was wrong.
    The 7905 is cold.
    The 7805 is hot!

    Is it OK or not?

  • Yes. The 7805 also supplies the digital part and need more power. The 7905 does not need much power because he needs only the analog part.

    You have check the polarity of all electrolytic capacitors. ? This is the most common error when the voltage is not correct.

    Good luck :)

  • Triple checked, capacitors OK!
    5 electrolytic and 1 tantalum are OK

  • Can you make HD-pics from the electronic plate.

    Have you a DC-power supply ?

  • Board – http://cl.ly/image/0j1U0V383z2G

    Couple pics with caps:
    http://cl.ly/image/16012t000W0Z
    http://cl.ly/image/1z0H2k1b2o2i

    All green points have -2.07V. It isn’t correct. Maybe something wrong with LT1054?
    http://www.flickr.com/photos/mutableinstruments/7711692322/sizes/h/in/photostream/

  • Yes, my power supply is DC.
    I tried three different power supplies.
    9V max 330mA
    12V max 300mA
    9V max 1800mA

  • Thanks is nice pics. i compare with assembly plate on web. In this time you can test the power signals on plate without all ic (exception LT1054,7805,7905). :)

  • Done.
    Point 2 — 11.21V
    Point 3 — -6.95V

    Red points — 4.96V
    Green Points — -6.41V

    (on this scheme – http://www.flickr.com/photos/mutableinstruments/7711692322/sizes/h/in/photostream/)

  • PS. I used DC 12V max 300mA.

  • Nope..
    LT1054 seems to be OK.
    pin Cap+ — 4.95V
    pin Cap- — -4.96V

    What else? =)

  • Step by step one ic into plate (without power supply!) and check every time the power points (power supply on). Stop when the Minus power point is sinking more than 0.5 Volts. This ic is broken ore the assemply area is not right. Also test the other ic.

    Good luck :)

  • no, sorry)
    Wrong pins in last comments.

    LT1054 (without all ic):
    V+ 11.3V
    V- -7V

  • Sorry my english is not so good. The LT1054 must be in the plate for tests. The power signals + 11.3V and -7.0V are good results. The 7905 input signal (Pin2, middle) is minimum -7.0 Volts.

  • I’ve put all ic on bottom part: processor and 7 closest ic — Voltage is OK (-7V).
    But if I put one (no matter which one) on the top part of board — voltage drops to -2.8 or -3.1V.

  • Small sketch for you – http://cl.ly/image/3Z2p3g1e3m1T

  • MMM... ? Please test with one IC in the top row (IC 10 TL074). I mean the ic TL074 need low power and the minus power is not sinking so match. When minus power down, i mean the LT1054 is broken ore C 51.

  • Done.
    -2.83V

    Without TL074 — 7.1V.

    Short? =)

  • I mean the LT1054 is broken :(

    Link for help:
    http://mutable-instruments.net/forum/discussion/2946/once-again-a-power-supply-section-problem/p1
    http://mutable-instruments.net/wiki/Troubleshooting_the_power_connection
    http://mutable-instruments.net/forum/discussion/884/missing-negative-voltage-3/p1
    http://mutable-instruments.net/forum/discussion/2337/fried-lt1054/p1

    Greetings from germany. Rolf

  • Thanks a lot!

    I’ll order new LT1054.

  • It is better two. The LT1054 is very sensitive for EMC (electromagnetic compatibility) and ESD ( electrostatic discharge). That affects all electronic components !

    Tip: Before you touch an electronic component ground yourself. Or touch the faucet in the kitchen.

  • Sorry, I don’t understand what you mean.

    You mean I should order 2 x LT1054?

  • Hello again!
    I’ve just received new LT1054 and they doesn’t solve the problem.
    Symptoms are the same.

    Maybe short?

  • oh.
    I was wrong.
    Voltage seems to be OK!!

    But sound doesn’t come =(

    What can be wrong?

  • Hello!
    I’ve done it!
    Re-soldered couple things and changed LT1054.

    All works great!

    Thanks a lot!

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