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MFOS Cv and Gate expander module

Discussion in 'Troubleshooting and Repair' started by darren adcock, Feb 6, 2019.

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  1. darren adcock

    darren adcock

    Sep 26, 2016
    Hi all.

    I can't get a photo of the project to here as I can't get an iphone 4 to talk to windows. So maybe this thread is a non starter?

    Anyhow, I've taken lot's of readings that may help in fault finding.

    This is quite a long thread which requires scrolling, maybe there was a better way to have posted this?

    The circuit i am having problems with is a "Music From Outer Space, CV and Gate Expander module".

    Here is the schematic; [​IMG]

    And panel wiring;


    The issue that i am having is that I am reading 5v on J10, J7 and J6. Also 5v on Led 1 (x16)

    I have the a duplicate of the module that is working and thought I'd just be able to compare the readings to figure out where i have gone wrong but 4hrs later and i'm non the wiser so thought I'd ask here.

    I've compared all wiring several times and nothing appears to be different between the two modules.

    All pots are turned anticlockwise to the furthest point. Switch 1 is switched to CV1

    The working module will be (A) and the faulty module will be (B)

    U1 and U2 have the same readings on their pins for each circuit.

    U3 has slight inconsistencies, scroll down

    U4 has the most inconsistencies and appears to be the area where the fault is, scroll down

    U5 has the same readings

    Q1 has inconsistencies

    I've included as many readings as possible. Please ask if more are needed

    U1; Pin readings
    1. -1v
    3. -19mv and gradually changes to -300mv the does the same again
    4. 12v
    5. Same as Pin 3
    6. -1v
    7. -1v
    8. -1v
    9. -1v
    10. Same as Pin 3
    11. -12v
    12. Same as pin 3
    13. -1v
    14. -1v

    U2; PIn readings
    1. -1v
    5. -1v
    6. -1v
    7. -1v
    9. -1v
    10. -1v
    11. -12v
    12. -1v
    13. -1v
    14. -1v

    U3 has inconsistencies on some pins;
    1. -10v
    2. 2v
    3. -1.1v
    4. 12v
    5. -00.2mV
    6. (A) 00.6mV (B) -0.4mV
    7. (A) 00.6mV (B) -0.4mV
    8. (A) 00.3mV (B) -0.1mV
    9. (A) 00.3mV (B) -0.1mV
    10. (A) 00.5mV (B) -00.2mV
    11. -12v
    12. -00.2mV
    13. (A) -00.9mV (B) -00.5mV
    14. (A) -00.9mV (B) -00.5mV

    U4 is where the fun begins with inconsistencies and where I suspect I've gone wildly wrong and haven't been able to work out how.

    1. (A) -00.1mV (B) 0.1mV
    2. 5v
    3. (A) 5v (B) 239mV
    4. (A) 00.2mV (B) 5v
    5. (A) 5v (B) 293mV
    6. (A) 00.2mV (B) -79mV
    7. 00.2mV
    8. (A) 00.2mV (B) 5v
    9. (A) 5v (B) 300mV
    10. 00.2mV
    11. 5v
    12. 00.2mv
    13. 5v
    14. 5v

    I also removed U4 and took readings from it's respective pin sockets.

    1. -00.1mv
    2. (A) 15mV and increasing (B) 140mv and increasing
    3. (A) is the same as pin socket 2 (B) 17mV
    4. (A) 56mV and increasing (B) -23mV
    5. (A) is the same as pin socket 2 (B) 13mV
    6. (A) -116mV and moving (should that be increasing?) towards 0v (B) 50mV and decreasing
    7. 00.1mV
    8. (A) -200mV and moving towards 0v (B) -55mV
    9. (A) 284mV slowly increases (B) 11mV
    10. (A) 51mV (B) -156mv and moves towards -300mv and then slows down
    11. (A) 270mV and increases slowly (B) Same as pin socket 10
    12. (A) -118mV and moves slowly towards -220mv then stalls (B) -126mv and moves slowly towards -320mV and then stalls
    13. (A) 275mV (B) -93mV
    14. 5v

    In. 12v
    Out. 5v

    C. 12v
    B. (A) 001mV (B) 5v
    E (A) no reading, or i'm miss interpreting the DVM, the screen falshes on and off with a reading of :0L (B) 5v

    What have i done?

    I swapped out U3, U4 and Q1 for known good ones to no avail, no surprise there. I checked all components to make sure i hadn't made a mistake several times (but this was after a few hours of fault finding so i may be mistaken, I checked all wiring.

    I have tried both modules CV and Gate function. I get no gate delay function on Module (B)

    I also noticed that the portamento function seems to be a bit limited in that there is only a tiny bit of change for the first bit of movement for the potentiometer. I am concerned that the panel wiring diagram is incorrect. In that connections x7 and x6 should not be connected as shown.

    Ok, so that was along post and maybe i lost you all along the way. I will endeavour to find a friend who has a camera phone tomorrow in my studios so i can get photos of the board and wiring to you.

    It is home time now and will be back in my studio for 9 in the morning.

    Thanks in advance

    Let me know if I could have worded/formatted this post better as concerned it's long and sprawling

  2. darren adcock

    darren adcock

    Sep 26, 2016
    Drew out the schematic this morning to make notes, got around to testing module B and it suddenly started working. Possibly I hadn't secured a component properly. Anyhow, apologies if anyone had spent time reading this. Concerned the problem may return. But for now it works and have resoldered all components for the gate delay section. So fingers crossed.
  3. darren adcock

    darren adcock

    Sep 26, 2016
    Cold solder on out of R13 before R14, D1 and x14 connection was the culprit. Must remember to check soldering more thoroughly when debugging.
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