Schematic VS how it's really wired

Discussion in 'General Electronics Chat' started by musicalavtech, Mar 17, 2013.

  1. musicalavtech

    Thread Starter Member

    Mar 23, 2012
    32
    3
    My marshall amp, a vs102r, is not making reverb. The return is good, but the send is not. As far as the reverb send...well after comparing the schematic to how it's actually wired, I found a possible reason.

    The first pic shows the circuit board as wired. There is a mystery resistor in the C6 slot.

    When checking with a meter, I found that C6 is common to R15, R16 and AG of the tube. It should be only common to R16 & R17. In the second pic, I modified the schematic to reflect how it is wired. The third pic shows the supposed correct wiring.

    Should I try to rewire to the correct schematic? It could be wrong. What about the mystery resistor? Just trying to get some reverb send going.

    [​IMG] [​IMG] [​IMG]
     
  2. tubeguy

    Well-Known Member

    Nov 3, 2012
    1,157
    197
    Very curious, (cap 'valued' as resistor). :confused: Has this ever worked ??
    I'll check my schematics later. (tomorrow) It makes more sense that it would be a capacitor as shown,
    but doesn't look right.

    I checked.. The schematic you posted doesn't jive .. where did you get it ??
    Is the Amp a 4210 ???
     
    Last edited: Mar 17, 2013
  3. musicalavtech

    Thread Starter Member

    Mar 23, 2012
    32
    3
    The schematic is off the web. I D/L another that is the same.

    The amp model is a VS 102R marshall. The cap is valued as a resistor as you say. The resister on the PCB is labeled as a cap. Weird.

    I realize manufacturers can make changes with no available docs. Makes it hard to troubleshoot.
     
  4. tubeguy

    Well-Known Member

    Nov 3, 2012
    1,157
    197
    That label is confusing. The circuit is a reverb return if anything - it's going through resistors to a grid (input) A typical tube amp reverb send has a driver transformer.

    Don't worry about the circuit just yet. Most dead reverbs are due to broken wires in the reverb spring. I haven't looked up this model yet Does this have a reverb spring unit?

    And did the reverb work at one time ?
     
  5. musicalavtech

    Thread Starter Member

    Mar 23, 2012
    32
    3
    It does have a spring reverb in it. I just pulled it and found a tiny hair thin wire broken from the coil of the transducer. That would explain things, but not explaining the schematic.

    I just got it a week ago, so I don't know if the verb ever worked. Of course the guy I traded my blues jr with, said there was no issues. HA!
     
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