Home Forums GuitarPCB Build Support SWAH help (solved)

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  • #9537
    jbasch
    Participant

    Hi everyone. I have recently built a SWAH v3B board. I have a 3PDT buffer board connected to it. When I engage the pedal I get a clean signal but no effect regardless of where I turn the knobs. I checked my voltages for the transistors and Q2 and Q3 seem a little off.

    with the knobs all turned fully CCW and a 9.0V input these are the readings I get:

    Q1: 7.0, 4.4, 3.17 (DSG)
    Q2: 4.93, 1.47, 1.17 (CBE)
    Q3: 4.92, 1.20, 1.33 (CBE)</div>

    My question is, do the low voltages help point me to the problem? Is it the transistors themselves or have I likely placed a wrong value component somewhere on the board?
    I noticed in my notes that I had used a 7.5k resistor for R27 since I didn’t have a 7.9k. Could that be my issue?
    Any thoughts are welcomed.
    Thanks!

    #9587
    jbasch
    Participant

    #9588
    jbasch
    Participant

    Thanks Barry. Posting the pics separate seems to work.

    #9589
    Barry
    Keymaster

    I cannot see from the photo but make sure your SWAH has the In and Out Tip wires crossed and led to the appropriate side of the Buffer Board. This build version for whatever reason got published with the In / Out pads on the opposite sides from what is expected symmetrically. It is discussed in the Build Doc and you can see how the wires are routed.

    I hope this image helps:

    #9590
    jbasch
    Participant

    Thanks. I did notice that when building the pedal over the weekend. I double checked and it is wired correctly.

    #9598
    Barry
    Keymaster

    There are 2 similar types of voltage regulator that I believe have different pinout. Check the datasheets on the one you have to be sure it is identical to the one called for in the build docs.

    We will need voltages of all three IC’s and the transistors.

    Proper Q voltages for comparison (all pots full CCW)

    Q1: (7.27 – 3.71 – 3.23 – DSG) <- Drain Source Gate not CBE

    Q2: (5.05 – 3.75 – 2.90 – CBE)

    Q3: (5.05 – 2.90 – 2.86 – CBE)

    I would also re-flow the project, test for continuity (see Crash Course Guide p.9) and use an audio probe (see guide on the Guides Page.

    #9601
    Barry
    Keymaster

    Be sure the Germanium Diode did not get even the slightest crack or chip while installing.

    They are incredibly flimsy.

    #9604
    jbasch
    Participant

    IC1: LM13700N

    1. 1.233
    2. Jumps around in mV
    3. 3.566
    4. 3.566
    5. 4.75
    6. 0
    7. 4.75
    8. 3.559
    9. 3.569
    10. 4.77
    11. 7.14
    12. 4.77
    13. 3.568
    14. 3.568
    15. Jumps around in mV
    16. 1.22

    IC2: TL074CN

    1. 3.568
    2. 3.512
    3. 3.566
    4. 7.14
    5. 3.558
    6. 3.557
    7. 3.565
    8. 3.33
    9. 3.565
    10. 3.566
    11. 0
    12. 3.566
    13. 3.566
    14. 1.489

    IC3: LM78L05ACZ

    I: 7.14

    O: 4.94

    G: 0

    Transistors are the same values as posted above.

    Thanks!

    #9605
    jbasch
    Participant

    on the germanium diode I get a forward voltage of .262 V.
    Visual inspection does not show any cracks but it is hard to see.

    #9606
    Billy
    Moderator

    What are you using to power it your voltage going in is low at 7.14v

     

    Your output on pin 14 of IC2 is really low check it’s seated correctly in its socket and check the underside to make sure all the socket pins are through the solder pads all pins except 4 and 11 should read around 4.5v half power supply given that your power in is 7.14v most of yours are reading around half power so pin 14 being that low will affect everything after it

    Its very easy to bend socket and IC pins

    and in your picture we can’t quite see all of pin 14

     

     

    #9607
    Cybercow
    Moderator

    Is that an ‘After Blaster’ PCB on the stompswitch? Also, can’t see the wiring for that or to the I\O jacks.

     

    #9608
    jbasch
    Participant

    I’m using a Dunlop DC brick. The voltage going into the SWAH board is 8.97v.

    #9609
    Barry
    Keymaster

    Mark it is a buffer board I believe and that should be examined as well.

    There are some voltage discrepancies. Not sure why the voltage is low on pin 11 (v+) of LM13700

    #9619
    jbasch
    Participant

    I checked IC2’s socket and all pins are completely through the holes and appear cleanly soldered. The IC is properly seated. I replaced it with another brand chip and I get the same readings. I’ll try resoldering pin 14 of the socket tomorrow in case it’s a bad joint.

    Following the voltage path from the schematic, I get a voltage drop from 8.95 (what the power supply is currently outputting to the board) to 8.25 across D4, then another drop to 7.08 after R28 (value correct) which is the input voltage the IC is seeing. I’m not familiar with how output at pin 14 is determined so I’m not sure what other components would affect the output.

    The stomp switch board is a 3dpt buffer board. I’ve confirmed that the IO from the stomp switch board to the main board is correct.

    #9620
    Billy
    Moderator

    All your IC v+ are 7.14v what voltage do you get on D4 if your power in is 8.97v you seem to be dropping almost 2v

    The solder joints on R28 look a little suspect so I’m thinking if you’ve got that voltage going in then your power to IC 1, 2 and 3 is only 7.14v it must be dropping prior to that and looking at R28 id suspect that if D4 is ok

    That still wouldn’t account for no effect however or the low output on pin 14 IC2 but one thing at a time and I’m sure we’ll get there

    #9621
    jbasch
    Participant

    8.97v in to 8.25v out across D4, then another drop 8.25v in to 7.08v out through R28. I’ll try resoldering D4 and R28 tomorrow and see if that helps.

    #9622
    Billy
    Moderator

    D4 seems fine I’d try reflowing R28

    Good news is parts of the circuit are doing what they’re supposed to do e.g. the voltage divider R29 and 30 is halving the voltage and IC3 is working regulating the voltage so as is normal its more than likely something simple like one or more dry solder joints

     

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