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Randall rh100w

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  • Randall rh100w

    Good morning, here's the issue: Randall RH100w guitar amp. There is power to the amp. Connecting the amp to a speaker with good cables through speaker out and input for guitar, produces a very low volume after a popping sound that cannot be altered by the master knob. Gain, channel switch, level and reverb knobs all work fine, affecting the signal as they should, so does the clean channel produce a clean sound as it should. Connecting the amp via line out to a audio interface does the same thing. Patching fx loop doesnt change anything. Regarding fx loop: send into audio interface produces same results, return produces No Sound. Fuse is not blown. Recently replaced Q12 and Q13. Upon inspection all solder looks clean, no cracks, no components look burned or disconected. Cannot figure out what the problem may be... I will attatch pictures if needed. Any information and help will be greatly appreciated.

  • #2
    Q12 & Q13 ... driver transistors ...?
    A schematic would help.
    Support for Fender, Marshall, Mesa, VOX and many more. https://jonsnell.co.uk

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    • #3
      Will post pictures of the circuit asap
      Attached Files

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      • #4
        Q14 & 15 are the output transistors and if they have failed, there will be DC voltage on L1 to ground.
        Have you got 0volts between L1 and ground?
        Have you got signal on L1?
        Support for Fender, Marshall, Mesa, VOX and many more. https://jonsnell.co.uk

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        • #5
          Yes and yes also Q10 failed last night, replaced this morning, failed again upon turning amp on thus changing the output while connected to a speaker, from the original post to a loud continuous buzz
          Last edited by FormulasFatalToTheFlesh; 11-24-2022, 03:00 PM.

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          • #6
            Did some studying, will check resistance of components connected to Q10 tomorrow,
            concluding there is a short somewhere and q10 cracking is a symptom, will post results.

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            • #7
              With no speaker load, what voltages, with respect to ground/0volt point, have you got on points 1 - 6?
              Attached Files
              Support for Fender, Marshall, Mesa, VOX and many more. https://jonsnell.co.uk

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              • #8
                I. 104
                ii. 104
                iii. 0
                iv. 0
                v. 0
                vi. 70

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                • #9
                  Point 1 & 2 is that 104 volts, 10.4 volts, 1.04 volts, 104mV?
                  There must be no more than 25mV between points 2 & 5.
                  Is R 24/25 correct value?
                  Support for Fender, Marshall, Mesa, VOX and many more. https://jonsnell.co.uk

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                  • #10
                    10.4 i suppose.
                    i am not an expert, those are the measurements i got.
                    I may not know what im doing.

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