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Thread: Gallien-Krueger 700RB II powers on but no sound

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    Supporting Member Tone Meister's Avatar
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    Gallien-Krueger 700RB II powers on but no sound

    Amp powers on and fuse holds but no sound from the speakers. CLIP light at INPUT emits steady yellow, fan is not working, pressing the TUNING MUTE does not light its red LED. POWER/PROTECT light at POWER switch should be blue, but instead emits steady red and does not change colors under any conditions thus far.

    0.00 VDC at speaker outputs
    0.001 VDC on FX Send
    0.002 VDC on FX Return.

    Injected signal into INPUT, get signal at TUNER OUT on patchbay, but no signal from FX SEND jack.
    Injected +4 signal into FX RETURN jack and get no sound from power amp to speakers.

    On the power amp board, someone has replaced D7 at one point as evidenced by it standing off the PCB by the full length of its leads. Measured 87.0 VDC across D7 in one direction and -86.9 VDC in the other direction. Can hear audible amplifier noise through power amp to speaker when measuring D7 with amplifier on.

    UPDATE: Received current schematics from GK which cover this board revision. Correct schematics attached
    Attached Files Attached Files
    Last edited by Tone Meister; 03-21-2017 at 07:40 PM. Reason: add correct schematic revision
    Quote Originally Posted by km6xz View Post
    "I have come to the conclusion that the biggest risk to amp performance/reliability and "tone" is players reading the internet, not bad tube brands, and certainly not the often argued over capacitors."

  2. #2
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    don't forget the joker g1's Avatar
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    How about the other power supply voltages, +/-40V, +/-35V, +/-15V ?
    Quote Originally Posted by Justin Thomas View Post
    In my ideal world, I'm not too loud - your room is too small!

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    Supporting Member Tone Meister's Avatar
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    Make sure to check out the updated schematics attached below.

    OK, we have power supply voltages out of whack all over the power amp. Since I have a number of measurements, this is a great opportunity to learn to organize it effectively in a post so its easy to follow for those helping out. Feel free to tweak my data organization, or lack thereof.

    We have +86V at R70 (expected +86V)
    We have -86V at R71 (expected -86V)
    We have +40V at R70 (expected +40V)
    We have -40V at R71 (expected -40V)

    We have +40.3V at R78 (expected +35V)
    We have -35V at R75 (expected -35V)
    We have -40.1V at junction of pin#1 of Q20, R41, R36, R40, R44 (expected +15V)
    We have -38.6 at junction of pin#3 of U4, R73, and neg side of C33 (expected -15V)


    DC MEASUREMENT POINTS

    Component ___________________ Expected _________ Measured
    Across R15 _______________________ 2.6V _______________ 0.013V
    Across R16 _______________________ 2.6V _______________ 0.018V
    Across R24 _______________________ 2.1V _______________ 0.000V
    Across R33 _______________________ 1.55V _______________ 0.000V
    Junction D7, pin#2 Q14, D9 __________ 4.9V ______________ -0.001V
    Junction D5, pin#2 Q11, R25, D11 _____ 4.9V ______________ -0.001V
    Attached Files Attached Files
    Quote Originally Posted by km6xz View Post
    "I have come to the conclusion that the biggest risk to amp performance/reliability and "tone" is players reading the internet, not bad tube brands, and certainly not the often argued over capacitors."

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    Supporting Member The Dude's Avatar
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    Presumably, you have 40V supplied to U5 since it's there on R78, but check it right on the leg of the regulator. You could have cracked solder or a burnt trace. Also, what are the other voltages right on that +15 regulator (U5)? Obviously, there's something radically wrong with voltages in that +-15v regulator circuit. Also wondering if we have a burnt or missing ground there somewhere.
    “Yeah, well, you know, that’s just, like, your opinion, man.”

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    Supporting Member Tone Meister's Avatar
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    Quote Originally Posted by The Dude View Post
    Presumably, you have 40V supplied to U5 since it's there on R78, but check it right on the leg of the regulator. You could have cracked solder or a burnt trace. Also, what are the other voltages right on that +15 regulator (U5)? Obviously, there's something radically wrong with voltages in that +-15v regulator circuit. Also wondering if we have a burnt or missing ground there somewhere.
    Finally a chance to get back on it.

    On U5 I get +39.9 VDC on the input and -39.9 VDC on both the output and adjust
    Quote Originally Posted by km6xz View Post
    "I have come to the conclusion that the biggest risk to amp performance/reliability and "tone" is players reading the internet, not bad tube brands, and certainly not the often argued over capacitors."

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