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Marshall VS100 Reverb works but ?? doesn't??

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  • Marshall VS100 Reverb works but ?? doesn't??

    Hey all new around here -
    My Marshall VS100 was 100% alive when suddenly the Clean channel reverb stopped working (But the Overdrive Channel Reverb perfectly works and the reverb box is OK) , for security I checked & re-soldered the RCA inputs [on the Preamp] and the Clean Channel Reverb Pot... nothing changed

    My question is why is the overdrive reverb working normally but the clean channel one isn't?? What are the key components involved with the clean channel reverb?
    Where should I start?

    {Marshall Valvestate VS100}

  • #2
    Reverb works perfectly in the overdrive channel , even tapped the box , but as soon as I switch to the clean channel the reverb cuts out , can't seem to detect any cold solder joints

    Comment


    • #3
      GM:

      Not sure if this is the correct schematic for your amp - VS100R-100W-Schematic.

      Does your amp have either molex connectors or ribbon cables? Maybe one of the wires came loose? Do a physical inspection of the wiring and components to make sure nothing became loose or disconnected.

      Comment


      • #4
        Originally posted by TomCarlos View Post
        GM:

        Not sure if this is the correct schematic for your amp - VS100R-100W-Schematic.

        Does your amp have either molex connectors or ribbon cables? Maybe one of the wires came loose? Do a physical inspection of the wiring and components to make sure nothing became loose or disconnected.

        Yep Those are the right schematics that I already own and was inspecting,it has molex connectors that are perfectly fitted right, it's an unusual issue , clean reverb doesn't work but the overdrive one does, I've tested the reverb box by crashing it , on overdrive it crashed, as soon as i switched to the clean channel reverb it immediately cut out

        Comment


        • #5
          Originally posted by TomCarlos View Post
          GM:

          Not sure if this is the correct schematic for your amp - VS100R-100W-Schematic.

          Does your amp have either molex connectors or ribbon cables? Maybe one of the wires came loose? Do a physical inspection of the wiring and components to make sure nothing became loose or disconnected.

          If only the famous ENZO would slip in & tell me what components are involved with the clean channel reverb on the VS100 lol

          Comment


          • #6
            It is possibly a routing issue and it doesn't help when Conn2 on page 2 turns into CONN1 on page 4!
            A printing error.

            Does pin1 of IC2 change state with ABSW1 switch TR3? ABSW2 TR2?
            Support for Fender, Marshall, Mesa, VOX and many more. https://jonsnell.co.uk

            Comment


            • #7
              IC5 is also part of the control switching and easily damaged by static.
              Support for Fender, Marshall, Mesa, VOX and many more. https://jonsnell.co.uk

              Comment


              • #8
                Originally posted by Jon Snell View Post
                It is possibly a routing issue and it doesn't help when Conn2 on page 2 turns into CONN1 on page 4!
                A printing error.

                Does pin1 of IC2 change state with ABSW1 switch TR3? ABSW2 TR2?
                By inspecting the actual PCBs it is no printing error, it is actually right , on the Daughter CON1 goes to the Pre-Amp , CON2 - From the Pre-Amp to the Power Module , CON3 becomes 'CON14T' , yeah it's weird I know

                Yeah They should change state I guess, after all IC2 is a general OP-Amp

                Comment


                • #9
                  IC2 is a selectable dual pre amp. Pin 1 is the control pin between Ch1 and Ch2.
                  That is where I would start and work backward looking for signal.
                  Support for Fender, Marshall, Mesa, VOX and many more. https://jonsnell.co.uk

                  Comment


                  • #10
                    Originally posted by Jon Snell View Post
                    IC2 is a selectable dual pre amp. Pin 1 is the control pin between Ch1 and Ch2.
                    That is where I would start and work backward looking for signal.
                    So you reckon I begin on pin 1 of IC2 on the Daughter right? I'll check it out ASAP thanks man

                    Comment


                    • #11
                      Pin 1 of IC2 will have DC on it that varies depending on the channel selected.
                      If pin1 is high then CH1 is selected. Pin1 low then CH2 selected.
                      Similar for IC3 and IC6 and indeed any of the M5201s in the amplifier.
                      Compare the output to the signal going in on pins 2 & 7 of each M5201.
                      Attached Files
                      Last edited by Jon Snell; 04-11-2020, 12:06 PM. Reason: Added partial schematic
                      Support for Fender, Marshall, Mesa, VOX and many more. https://jonsnell.co.uk

                      Comment


                      • #12
                        Page 4 is the daughter board, and the 13 pin connector is CON1 on THAT board. Page 2 is the preamp board, and the 13 pin connector on THAT board is CON2. Not a typo. They are two different connectors on two different boards. They DO connect to one another via wires though.

                        Your problem is not the reverb, it is either the send or return from that channel. There are not separate reverbs for the channels.

                        Page 4 long connector, pin 6 is the reverb return signal. We know it works because one channel reverb works. Follow it down to C17, C18, each going to a channel reverb level control. IC2 is a 5201 switching IC Marshall likes to use. There are a couple more of them in the preamp. CON1-11 is the control for that IC. It decides whether the IC passes along VR2 or VR3 signal. That is it. We know that one of those cap/pot/IC paths works, so something about the other path is frotzed. SO apply some steady signal to the amp - I just use a CD player myself - and scope the two reverb controls. Is there signal on the top lead of BOTH or is it missing from the dead channel? Is there signal on the wipers? Both pots should act the same. tes? That leaves the IC, and if you don't have a new one, try swapping it for one from the preamp. If the problem remains, it wasn't the IC. If the reverb starts working but now the preamp has some new issue, then teh IC was bad. Oh and better watch the control signal at pin 1 of the IC. Does changing channel change that control voltage?

                        By the way, my title is "The Mighty", not the "Famous".
                        Education is what you're left with after you have forgotten what you have learned.

                        Comment


                        • #13
                          Originally posted by Enzo View Post
                          Page 4 is the daughter board, and the 13 pin connector is CON1 on THAT board. Page 2 is the preamp board, and the 13 pin connector on THAT board is CON2. Not a typo. They are two different connectors on two different boards. They DO connect to one another via wires though.

                          Your problem is not the reverb, it is either the send or return from that channel. There are not separate reverbs for the channels.

                          Page 4 long connector, pin 6 is the reverb return signal. We know it works because one channel reverb works. Follow it down to C17, C18, each going to a channel reverb level control. IC2 is a 5201 switching IC Marshall likes to use. There are a couple more of them in the preamp. CON1-11 is the control for that IC. It decides whether the IC passes along VR2 or VR3 signal. That is it. We know that one of those cap/pot/IC paths works, so something about the other path is frotzed. SO apply some steady signal to the amp - I just use a CD player myself - and scope the two reverb controls. Is there signal on the top lead of BOTH or is it missing from the dead channel? Is there signal on the wipers? Both pots should act the same. tes? That leaves the IC, and if you don't have a new one, try swapping it for one from the preamp. If the problem remains, it wasn't the IC. If the reverb starts working but now the preamp has some new issue, then teh IC was bad. Oh and better watch the control signal at pin 1 of the IC. Does changing channel change that control voltage?

                          By the way, my title is "The Mighty", not the "Famous".
                          Thanks so much for the important info :P , just when my multimeter decided to die - Originally I excluded the fact that any ICs would be dead (shouldn't the main fuse blow if an IC is down??) , and no worries for me, I've got more VS100 original spare parts than Marshall itself

                          I'll try to test all of these things , I'm also re-soldering ALL joints on the Pre-Amp just to make sure that we're not into cold solder territory

                          Comment


                          • #14
                            (shouldn't the main fuse blow if an IC is down??
                            Seriously, why would you think that?

                            Even if the IC had turned to charcoal, it probably won't blow a fuse, especially the main fuse. ICs can fail in many ways, just like other parts. Imagine you snapped off a voume control, the fuse won't blow from that. Likewise, inside an IC are tiny circuits, and one broken conection in there is all it takes to kill it.

                            The whole point here is to systematically follow the signal path to see where the signal goes missing. We don't just start replacing things with a "maybe it is this" approach.
                            Education is what you're left with after you have forgotten what you have learned.

                            Comment


                            • #15
                              Originally posted by Enzo View Post
                              Seriously, why would you think that?

                              Even if the IC had turned to charcoal, it probably won't blow a fuse, especially the main fuse. ICs can fail in many ways, just like other parts. Imagine you snapped off a voume control, the fuse won't blow from that. Likewise, inside an IC are tiny circuits, and one broken conection in there is all it takes to kill it.

                              The whole point here is to systematically follow the signal path to see where the signal goes missing. We don't just start replacing things with a "maybe it is this" approach.
                              My original thoughts too, my local tech told me some time ago that the fuse would blow only if there is a shorted semi-conductor / transformer , apparently he doesn't know the rest of the story , which brings me to consider that one of the ICs might be tapped

                              Comment

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