Zeppelin Design Labs

Voltage is off on Q1

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  • #4669 Reply
    VerbalDave
    Participant

    Hello, I’m testing this latest Cortado I had an intern put together(teaching him how to solder). The bias is able to be set to .075 easily, however, it requires about double the pre-amp gain as the other cortados I have built. When I measure the voltages the middle pin on Q1 is registering around 44V. All the resistors are showing the correct value, but I’m trying to figure out why that voltage is almost double of what it should be. Any ideas?

    #4670 Reply
    brach
    Moderator

    If pin 2 of Q1 is at 44V then pin 2 of Q2 should also be at 44V…if not then Q2 isn’t making good connection to the circuit, which could cause these symptoms. You might want to re-flow your intern’s solder joints for good measure.
    Note the voltages on the picture in this post:

    setting the bias current (scratchy Cortado)


    Are there any other voltages that aren’t matching up to the voltages on this picture?
    Good luck. Let me know.
    -Brach

    #4673 Reply
    VerbalDave
    Participant

    Yeah with the picture, my phantom is coming in at 45V on both pins 2 and 3. At the pin 2 on q1 it is 45V and on q2 it is 45V. On the resistors R4 is 19.55V and R1 it is 45V

    #4686 Reply
    brach
    Moderator

    Have you re-flowed all the joints on Q1 (and the rest of the board for good measure)? Are pins 2 and 3 shorted?…what’s the resistance across them? If R1 is measuring 3.3M ohms, then it seems like pins 2 and 3 are shorted…either by a solder short or internally. If it seems like it’s an internal short then remove Q1 from the pcb and measure across pins 2 and 3 with an ohm meter. From my experience, this type of problem is usually an assembly issue.
    Keep me posted.
    Good luck.
    -Brach

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