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Troubleshooting a "Refreshed" Fender SF Pro Reverb

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  • #16
    Originally posted by Chuck H View Post
    Ok. The question now is *Why not?*

    Because it should. According to the schematic it should be tied to pin 3 of that same socket and then to a 25uf cap parallel with an 820r resistor on the board that are to ground.

    With that pin not connected the tube will not conduct. This could explain the low volume and lack of reverb.
    I see exactly what you're saying when looking at the schematic about pin 8. I've taken some pictures of the chassis today so you can get a better look at the wiring for V4.Click image for larger version

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    • #17
      Ok!!! Well, somebody's been in there eh?

      The orientation of the reverb transformer looks to be 90 different from what I'm use to in earlier amps. That threw me off for a second. I think those cathode circuits going to the RCA jack frames for ground isn't stock, but I've not been inside one of these amps before. Still, the component values for the V4 cathode circuit look right so try connecting pin 8 to pin 3.
      "Take two placebos, works twice as well." Enzo

      "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

      "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

      Comment


      • #18
        Originally posted by Chuck H View Post
        Ok!!! Well, somebody's been in there eh?

        The orientation of the reverb transformer looks to be 90 different from what I'm use to in earlier amps. That threw me off for a second. I think those cathode circuits going to the RCA jack frames for ground isn't stock, but I've not been inside one of these amps before. Still, the component values for the V4 cathode circuit look right so try connecting pin 8 to pin 3.
        Thanks for your input Chuck. So (just to review) I need to connect pin 8 to pin 3 using a jumper wire, correct?

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        • #19
          Originally posted by Sleet View Post
          Thanks for your input Chuck. So (just to review) I need to connect pin 8 to pin 3 using a jumper wire, correct?
          Correct.

          No guarantees how it will work out though. I can't know what sort of changes may have been made to the amp. No risk of damage to anything.
          "Take two placebos, works twice as well." Enzo

          "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

          "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

          Comment


          • #20
            Am I seeing things or is pin1 connected to a heater wire? (pin8 is without connection)


            Click image for larger version

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            Last edited by g1; 11-18-2019, 01:21 AM. Reason: add pic
            "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

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            • #21
              Originally posted by g1 View Post
              Am I seeing things or is pin1 connected to a heater wire?
              It looks like that in one of the shots. Furthermore, it's hard to tell otherwise in all but one of the other shots. But I don't think so.
              "Take two placebos, works twice as well." Enzo

              "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

              "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

              Comment


              • #22
                see edit, post #20
                "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

                Comment


                • #23
                  Originally posted by g1 View Post
                  Am I seeing things or is pin1 connected to a heater wire? (pin8 is without connection)


                  [ATTACH=CONFIG]55989[/ATTACH]
                  Yes, that's how it is currently connected, or not, in the case of pin 8. Pin 8 appears to have some traces of solder on it. The amp, to my novice eyes didn't seem to been modified in the past. Having said that, it certainly doesn't seem to be wired correctly..... I attempted to get as much detail in the photos as I could.

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                  • #24
                    " I think those cathode circuits going to the RCA jack frames for ground isn't stock, but I've not been inside one of these amps before."

                    Actually, this is indeed stock. I have one in my shop right now that is this way.
                    It's weird, because it WAS working fine.....

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                    • #25
                      Originally posted by g1 View Post
                      Am I seeing things or is pin1 connected to a heater wire? (pin8 is without connection)


                      [ATTACH=CONFIG]55989[/ATTACH]
                      Originally posted by Chuck H View Post
                      It looks like that in one of the shots. Furthermore, it's hard to tell otherwise in all but one of the other shots. But I don't think so.
                      I see what you mean now Chuck. That heater wire isn't going to pin1, but tucking around under and going to pin 4/5.
                      "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

                      Comment


                      • #26
                        Originally posted by pdf64 View Post
                        Just noticed the above, 'coupling caps' seems odd, was that just a terminology error, or have ecaps been used for coupling purposes?


                        Confused by this, the neon couldn't flash if it's been removed from circuit?

                        My take on the thread is that
                        1/ the amp seems to have been modded as the master doesn't seem to affect the normal channel (true?); so need to verify the circuit to its intended schematic.
                        2/ from the bent front panel, the master volume may have received a massive bash, may be broken, and given the symptoms must be replaced, or just taken out of circuit. Hardwire the pull boost switch in the non boost mode.
                        3/ a voltage survey and idle plate / cathode current measurements (eg resistance and volt drop from OT CT to each plate) would be very useful.
                        I just reread all of the comments and postings, thanks to one and all. I would like to narrow the field of possibilities, a process of elimination to get to a solution. I seem to have a partially functioning amp with the power section working and part of the preamp working. The reverb and vibrato channel are malfunctioning. Based on the schematic I think I need to troubleshoot the signal path and confirm the function of the master volume.

                        I do have a signal generator and scope to help out. Voltage and current survey as pdf64 suggested might also be enlightening. Any pointers or starting points would be greatly appreciated.

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                        • #27
                          Did you tie pin 3 & 8 of V4 and now are still having the problem?
                          (sorry about the heater wiring distraction)
                          "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

                          Comment


                          • #28
                            Originally posted by g1 View Post
                            Did you tie pin 3 & 8 of V4 and now are still having the problem?
                            THIS^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                            "Take two placebos, works twice as well." Enzo

                            "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

                            "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

                            Comment


                            • #29
                              Originally posted by Chuck H View Post
                              THIS^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                              I went and tied pin 8 to pin 3 and sure enough I'm now getting full output from the vibrato channel. I believe that in process of changing out the capacitor tied to pin 3 I seem to have forgotten to connect the capacitor lead across to pin 8. All of the tone controls and the MV are all functioning with both channels. I haven't had time to reconnect the reverb tank (getting late), but the I'm pretty sure it's going to work.

                              Thanks so much to all the contributors in this thread. I may be back with a few more questions related to this amp

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