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Rodgers 990 Stops Issues

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  • Rodgers 990 Stops Issues

    I've been gradually restoring a Rodgers 990 organ that had various power supply problems, but am now trying to troubleshoot some of the stops. Four different stops are operating improperly, exhibiting various combinations and permutations of stuck on, stuck off, and indicators that disagree with what is being heard. I've got the Technical Manual, but it appears to be quite deficient, so I'm requesting 15 minutes of discussion with somebody who still remembers how these beasts work. My background is retired electrical engineer with Wurlitzer training, so I should be able to find my way around a 990 with minimal assistance. Looking forward to working with folks on this site!

  • #2
    Update: Working on Stop stuck ON, found weird voltages around Q25, D25, & D26. Removed transistor -- it's fine. Diodes seem to be OK. Can't figure out what's downstream that could be causing trouble. Help!!!


    • #3
      OK, I was looking at weird voltages because I was probing a spare circuit! (Guess I don't quite know everything about a 990 yet.) So all is well with Q25, D25, & D26 on the actual stuck Stop. The Stop switch works fine, and the indicator turns on and off. But the sound is still stuck on, and it's very annoying, because it just happens to be the 1 1/3' Nineteenth Stop. So here's the real question: On schematic drawing number 1396F, the cathode of D26 is shown to connect "TO STOP." Where exactly is that destination? (Which schematic, and which component?) That's where the problem is, but I can't figure out where "there" is! Thanks in advance to anybody who knows their way around this beast.


      • #4
        Check Q301 for the 1-1/3 ft. stop on Rack 5, the Great Ganging Board. That's the transistor that ultimately stops keying voltage from reaching the Great Diapason Keyer when the stop is off. If it is open, the stop would always be on. See schematic 1295, upper LH corner. If you ground the bus that the diodes collect (emitter of Q301), it should turn off the stop. That would tell you that Q301 isn't turning on to shunt the keyer voltage to ground. Q301 could be the problem, or the capture system voltage to turn on Q301 could be interrupted--possible broken wire or defect in the capture system.

        For this problem, the manual suggests QCR 25 might be defective, and R's 26, 24, and 42 might be open if the stop will not turn off--these are all on the combination action system.
        Last edited by toodles; 09-30-2018, 09:58 AM.


        • #5
          Wow -- Thank you so much!!!


          • #6
            OK, I'm down to my last problem. Everything on the 990 now works except that the Lighted Capture System will not capture a Stop that is turned OFF. In other words, I can set a Stop to ON and save it to memory, but if I set the same Stop to OFF and then save it to memory, it's still on when I read back the setting. This is true for all Stops and all keyboards. Needles to say, my memory is filling up with ON Stops! Something has failed that writes "zeros" to the core memory. Any ideas?


            • #7
              Can you set a stop "off" with the "Hold-and-Set" method? (Press a piston that is already set, then, while holding in the same piston but NOT the set piston, turn the stop off, wait a half a second, then release the piston. Then check to see if it set as "off.")

              The magnetic core memory erases all settings each time a piston is depressed as part of the "read" cycle (so-called "destructive read.") Then it immediately re-writes the registration memory by checking for "on" stops, continuing to do so as long as the piston is held in. Thus, holding a piston while changing combinations will alter the recorded registration for that piston without the use of the set piston.

              If this method works, and I suspect it will, you probably don't have anything wrong with the memory system itself. Other than that, I can't tell you why it isn't setting properly with the set piston. Maybe some kind of trouble in that circuit. But you can theoretically do without the set piston by doing all your registrations with hold and set.
              Church: Allen MDS-45 with Allen MIDI-DIVISION-II expander
              Home: Allen Renaissance R-230 with expanded four-channel audio and MIDI-DIVISION-II
              Shop: Bunch of organs in varying conditions, some good, some not...
              Half of an incredible two-man organ service team -- servicing all the major digitals in Arkansas churches


              • #8
                OK I'm going to help out the Hurdy Gurdy Man here since he is talking about my Rodgers 990 for those who had not put the two of us, and this one cranky organ together.

                Jbird, as always I like your ideas. You, and Toodles can be quite creative. So I thought I would try editing combination action memory settings by your method without using the set piston. So here is what happened. I pressed the #1 combination action button, and recalled whatever it held in storage. Then I pressed, and held the #1 button by itself. While holding the button the already illuminated stops were all pulsing their lamps at a rapid rate. So I turned some of them off, and released the #1 button. Then I hit the combination clear button. Next I hit the #1 button, and everything that had been on came on, and those that I had deleted stayed off! I tried this several more times with gleeful success.

                So I said let's clear out all of the combination action presets. So I pressed the #1 button, and held it. Then I pressed the combination clear button, and then released both buttons. Everything was clear. I went back at this point and pressed, and held the #1 button. I selected a handful of stops. They were not doing the fast flashy thing. I released the #1 button, and the stops stayed lit. Then I hit the clear button, followed by hitting the #1 button for that moment of testing truth; total stop illumination darkness. I repeated the last programing sequence again with the same results. So then I decided to check my other combination action piston selections. There was nothing, they are all now totally erased / non-responsive. It would appear that I have successfully killed the entire combination action memory system. I can occasionally get one of the manual specific pistons to work, but I can not reprogram it, and they do not work consistently.

                So what have I done???
                Until The Next Dimension,
                Admiral Coluch.


                • #9
                  Did this organ have a catastrophic failure in the past--like a lightning strike or big surge near it? It is seeming like fixing one problem causes another failure, which is indicative of systems that are partially damaged.

                  Look to make sure all power supply voltages are correct and properly filtered as a start. And make sure the combination action has solid connections to its power sources.

                  As to the combination action, the piston disconnect and temperature compensated power supply are the only two function blocks that are for the entire organ, the other blocks are either per division or per stop. Check out the piston disconnect circuit and the temp compensated power supply.


                  • #10
                    Ok here are today's updates.

                    In terms of the piston disconnect circuit I would have to say it sure seems to work very well for something that could be damaged. It doesn't matter if you want to clear a registration that has been manually pulled, or one that has been selected from the combination action, it clears them all. I suppose you could tell me that is all well, and good, but the circuit could still have some sort of hidden damage that is causing underling problems with other circuits.

                    As for a catastrophic event in it's history the instrument survived 34 years in the church with no issues like this. The bell tower was struck by lightning several times over the years, because it has a copper slanted roof. More than one electronic bell system was destroyed when this happened. None of these strikes ever affected the organ, since it had no connection, or circuitry affiliation with the bell tower.

                    Ok now to the interesting update. Since I scrambled the memory system earlier this week I have not been able to call up any memory presets. Yesterday I tried to call up presets as I was beginning practice and they did not function. So I practiced for about 15 minutes and tried a preset, and it came up. Plus the ones I had changed were still in place. I know where one might go with this. You would think that this points to mis-adjustment of the temperature variance pot for the memory system. I would too. Here is where it gets more interesting. Today when I went to practice all of the presets worked as soon as I turned the organ on. When pressed, and held the preset buttons would cause the fast flashing of the stop lamps, and I could add, or remove stops, and the preset would write to memory. So this seems better.

                    So I went to push the system further. I tried to select a different preset after an initial preset was loaded. The system would not make the change. I can clear the initial preset with the master clear, and select a different preset, and all is well. Plus I can not select a divisional preset if a main preset is set. If I clear the main preset, sometimes I can select a divisional preset. I never can add or delete stops from a divisional preset.

                    So I hope this has thoroughly confused everybody, as much as it has confused me.
                    Until The Next Dimension,
                    Admiral Coluch.


                    • #11
                      I'm back to the misadjusted temperature-compensated power supply! The service manual shows a graph, from which an appropriate voltage can be derived at a particular room temperature. But the graph is not in agreement with the schematic -- 11V versus 13.5V @ 70F -- and neither actually state where the voltage reading should be taken. Is there a more precise procedure by which the power supply voltage can be dialed in? I'm imagining something like "Turn the instrument on and let it stabilize for 30 minutes, then adjust R257 until voltage at the emitter of Q254 is 13.5V." I'm kind of inferring that from the schematic, but there are still too many unknowns. What is actually the correct voltage at 70F? Across which two points should I attach the leads of the DVM? How long should the organ warm up?


                      • #12
                        My drawings indicate voltage should be measured after organ is on for 5 minutes. See the notes above the temperature graph, upper left hand corner or dwg 1396. I have Rev. F.

                        I would go by the graph for the voltage, as "-13.5" seems to just be a reference name and what is marked on the board.

                        See attached Field Service Bulletin, as it indicates where the voltage should be set.
                        Attached Files


                        • #13
                          Thanks, Toodles! That should get me where I need to go.


                          • #14
                            Beware rebel fighters -- the Rodgers 990 Death Star is fully functional once more!

                            I do believe that the catastrophic event was previous repair technicians who ignored the ground warnings. Most of the trouble was in the area with the 15V "ground," so if that was ignored, it would explain a lot of the failures:

                            1. Repaired lighted capture system power supply by replacing Q41.
                            2. Repaired temperature compensated core memory power supply by replacing Q254 and adjusting voltage per service bulletin.
                            3. Replaced 22 bulbs in stops and lighted music rack.
                            4. Repaired several stops by replacing SCR Q19.
                            5. Convinced 1 1/3 Nineteenth stop to behave by resoldering R311 to great ganging board.

                            Mucho gracias to all the Organ Forum folks who helped educate this former Wurlitzer repairman, especially JBird604, Toodles, and Darth-Car himself. The galaxy will never be the same!


                            • #15
                              Glad to know you got it up & running!