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  • Rodgers Concord 755 power supply failed

    We have a Rodgers Concord 755 (at home) that has experienced several power supply failures. The Rodgers tech has replaced the same resistor three times - the last time he put in a higher wattage component that has worked for a while. Like the other times, the organ's output suddenly ceased. The stops keep their memories - just no sound output.

    The power supply has this number on it: ROC 5013-309 (the 09 is hand lettered). The resistor that has burned through is in the upper left corner of the PS.

    Can someone point me to a source for rebuilding, repair, or replacement of the PS? The Rodgers tech doesn't seem interested in chasing this down.

    I can do electronic repairs but don't have any schematics on the unit. Any help would be greatly appreciated.

    (Have considered Hauptwerking this unit but not ready to spend the money - yet.)

    Thanks.

    Rob

  • #2
    Look closely at how the power transistors on the power supply are connected to the PCB. They used connectors that over time the plastic is failing which could be causing problems with the resistors if they are in the same area. I have a friend that found the connectors crumbling when they were touched. The final fix was to solder them to the transistors. I understand there is a tech note on this problem.

    Pete

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    • #3
      Thanks, Pete.

      I always like to have a set of schematics when I work on gear. Do you, or anyone else, know where I can buy them?

      Rob

      Comment


      • #4
        I have a Rodgers 820 that had begun powering off on its own. The first time I would power it on each day, it would stay on the longest (about 2 minutes). Thereafter, it would power off after about 30 seconds. Now it will not power on at all. I thought it was maybe the keylock power switch but I have tried working around that with no luck. I have looked closely at the power supply and can see no problems. Everything looks and tests fine. Any ideas?
        Dan Royster, MA, MS
        Guidance Counselor
        Digital Design & Engineering Counselor
        Knight High School
        Palmdale, CA

        Home: Rodgers 820....I love this instrument! Has the connection for the pipe augmentation; How to get it to MIDI?
        Church: Allen 301B (I think?) ADC....all features of an Allen ADC 4000; Would like to add MIDI to it

        My Professional Profile: https://www.linkedin.com/profile/pub...public_profile

        Comment


        • #5
          Originally posted by dkroyster View Post
          Any ideas?
          I'm not a tech like John (JBird604) or Dave (tuscondave), nor do I have extensive knowledge of electronics like Don (don60) or Charlie (toodles), but the thought that immediately comes to mind is that one should go to the source of the power. Is the power coming from the wall a stable source of electricity? Do you use a surge protector?

          I know this is a 3-year-old thread, but I thought Rodgers schematics could be obtained directly from their website. I could be wrong about that, as there have been changes to their website since this thread was originally posted.

          Other than that, I'd advise waiting for the techs on the Forum to weigh in. They're very good.

          Michael
          Way too many organs to list, but I do have 5 Allens:
          • MOS-2 Model 505-B / ADC-4300-DK / ADC-5400 / ADC-6000 (Symphony) / ADC-8000DKC
          • Lowrey Heritage (DSO-1)
          • 11 Pump Organs, 1 Pipe Organ & 7 Pianos

          Comment


          • #6
            That is one Rodgers model that I actually have not serviced AFAIK, and it's a bit of an unusual model too, one of the models Rodgers quickly brought to market in the early 80's when their MICASKO system went bust and they had to resurrect the 1970's time-share system and start making organs with it while they scrambled to remodel MICASKO into what became the highly successful serial-keyed organs of the 80's.

            Looking at the brochure and technical details on the Rodgers site, it looks quite impressive to me. A very well-designed and laid-out model with amazing flexibility in voicing and finishing. I hope you have enjoyed it and will be able to get it fixed so you can enjoy it for years to come.

            The power supply looks very straightforward to me. One quirky thing about it is that the keyswitch doesn't pass power directly to the power supply, but actually operates a relay that then turns on the power to the supply. You might take a look at the relay to see if it's contact points have gone bad.

            Also, there is some completely mysterious component (to me anyway) that is in series between the relay and the input to the power supply. It might be some kind of resistor that serves to limit the inrush current to the power transformer, possibly to protect the relay's contacts. It is drawn on the schematic as a resistor within a circle, with the letter "T" inscribed inside the circle, and "5 ohms" printed below it. Could be some kind of resistor that gradually becomes fully conductive over a period of a few seconds after power is applied. Some other tech on the forum may be able to tell you for sure.

            But whatever it is, that little jewel looks like a prime suspect to me. If it somehow has gotten degraded and began to "open" rather than to "close" when it warms up, that would explain your symptoms. I wish I knew what it looked like, but oddly enough it's not even given a part number in the schematic, much less an explanation of what it might be! It looks like there is a BLUE wire coming off the relay leading to this mysterious part, and a blue/white striped wire that leads from this part to the transformer.

            BTW, before the power actually goes into the transformer, it goes through another "mystery" thing-a-ma-jig, which appears to be a sliding switch that is used to set up the organ for various power line voltages. That is another possible place for a problem to develop, so you might look at that thing and perhaps the wobble and slide the switch mechanism around before re-settling it on your correct voltage (120 volts in the US, but you don't give your location).

            Other than those two items, I can only guess that you might have a power transformer that's gone out, and that will be a serious problem indeed. Please check these items out and let me know what you find.
            John
            ----------
            *** Please post your questions about technical service or repair matters ON THE FORUM. Do not send your questions to me or another member by private message. Information shared is for the benefit of the entire organ community, but other folks will not be helped by information we exchange in private messages!

            https://www.facebook.com/pages/Birds...97551893588434

            Comment


            • #7
              John, That resistor with the circle with the "T" is a thermistor. It adds resistance until it heats up from the current inrush and then go down to being almost a short. As you suspected it is used to slow down the inrush of current. These little units have a high failure rate but are dirt cheap to replace. To check to see if this is the problem, just put a wire across it to short it out. It will not harm anything to try this and see if the organ comes on ok.

              Comment


              • #8
                Originally posted by jbird604 View Post
                Also, there is some completely mysterious component (to me anyway) that is in series between the relay and the input to the power supply. It might be some kind of resistor that serves to limit the inrush current to the power transformer, possibly to protect the relay's contacts. It is drawn on the schematic as a resistor within a circle, with the letter "T" inscribed inside the circle, and "5 ohms" printed below it. Could be some kind of resistor that gradually becomes fully conductive over a period of a few seconds after power is applied. Some other tech on the forum may be able to tell you for sure.

                But whatever it is, that little jewel looks like a prime suspect to me. If it somehow has gotten degraded and began to "open" rather than to "close" when it warms up, that would explain your symptoms. I wish I knew what it looked like, but oddly enough it's not even given a part number in the schematic, much less an explanation of what it might be! It looks like there is a BLUE wire coming off the relay leading to this mysterious part, and a blue/white striped wire that leads from this part to the transformer.
                .
                An NTC (negative temperature coefficient) resistor before the transformer primary is part of the package that eliminates the turn on whomp on the speakers of an amp. As organs are frequently called on to sit silently, then jump in at a loud volume, paralling the NTC resistor with a relay contact controlled by a delay timer would also be wise design. Otherwise the NTC resistor could go cold and reduce volume for a few seconds in that sort of performance.
                I've salvaged 6 of the green NTC resistors out of dead PCAT power supplies, no fault with that part in any of them. When I compensate for the DVM battery on the 200 ohms scale with a known 2 ohm resistor, they all read within 20% of the 2.5 ohms they are labeled with. The green ones are *****ese, the black ones labled "CLxx" are GE made in USA. I've been installing the black ones per advice on diyaudio.com to prevent my bigger amps from dimming the lights when I turn them on. Be aware when checking, NTC resistors are usually wrapped with heat shrink to keep them hot longer, so you can't read the numbers typically.
                The relay contact can be a less reliable component at 20-30 years, but one that can be cleaned with a file (not sandpaper) in most cases. It should be possible to debug this part of the circuit with a $30 DVM. As the energy is very high in this part of the circuit, read and heed the safety rules in the sticky thread.
                As far as power transformers, I find a lot of loads on power transformers (ie electrolytic caps) to be more failure prone past the 20 year boundary than the transformer itself.
                I just pulled a DVD drive made in April 2006 that had been keeping my Pentium 4 PC from booting when the room temperature went down to 55 last week. The six peanut sized 47 uf 6.3 v electrolytic caps are measuring 1.7 kohms max. Surprise, surprise.
                After a DVM has proved that 120 VAC is going into the transformer after a while (usually about a 3 second delay with the NTC resistor) one should check the two big caps after the transformer that the DC voltage is about 80% of the rating printed on the side. If the AC in is good, and the DC out is zero, I would start checking the rectifiers in addition to replacing the e-caps. Resistors are also used as "fuses" in the part of the circuit by savvy companies out to save the $3.70 a fuse holder and fuse costs. A 1 watt ten ohm resistor costs about 12 cents. I wouldn't replace rectifiers or burnt resistors between transformer and e-caps without replacing the e-caps, with long life versions. Some people believe a $100 cap meter is necessary before replacing a $4 e-cap, I by contrast view them as geriatric after 20 years (pro instruments) or 10 years (cost cutter guitar amps) or 5 years (PC and TV parts)
                Last edited by indianajo; 02-23-2015, 11:54 AM.
                city Hammond H-182 organ (2 ea),A100,10-82 TC, Wurlitzer 4500, Schober Recital Organ, Steinway 40" console , Sohmer 39" pianos, Ensoniq EPS, ; country Hammond H112

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                • #9
                  It's settled then... TO THE poster with the Rodgers 820 (not the 755 owner who started this thread): Temporarily jumper across that little item and see if the organ starts right up and continues to play. If it does, you should seek out a replacement for the part.

                  TO THE OP whose 755 keeps burning out a PS component: Call Rodgers and see if they will send you the schematics at no charge. They are available for most models as PDF files, but they are quite large files, possibly too large to send via ordinary email.
                  John
                  ----------
                  *** Please post your questions about technical service or repair matters ON THE FORUM. Do not send your questions to me or another member by private message. Information shared is for the benefit of the entire organ community, but other folks will not be helped by information we exchange in private messages!

                  https://www.facebook.com/pages/Birds...97551893588434

                  Comment


                  • #10
                    Hi,

                    I think, if memory serves me right that on those Mikasko organs, there was an access code that had to be punched in, and then the computer would somehow latch the power supply into the on position. To test the organ, there was a by-pass switch on the power supply.

                    Is any of this correct? It is so cold up here, maybe my mind is a little frozen up too.

                    AV
                    Last edited by arie v; 02-23-2015, 12:34 PM. Reason: spelling

                    Comment


                    • #11
                      I think you're correct, Arie, but I've never even seen a working MICASKO organ. Apparently that series flopped so quickly that not a single one got sold here. I seem to recall seeing a LOT of promotional material about the MICASKO system in the Rodgers dealer showrooms. I think they had really bet the farm on it but it flopped quicker than the Edsel Ford.

                      The 820 this customer has uses the "CMOS" technology Rodgers used throughout the 70's, which they had to quickly trot out for a re-run in the early 80's when MICASKO went up in flames. The 820 has a simple keyswitch on/off system, complicated by the relay and of course by this negative-thermistor component.
                      John
                      ----------
                      *** Please post your questions about technical service or repair matters ON THE FORUM. Do not send your questions to me or another member by private message. Information shared is for the benefit of the entire organ community, but other folks will not be helped by information we exchange in private messages!

                      https://www.facebook.com/pages/Birds...97551893588434

                      Comment


                      • #12
                        I wanted to let each of you know that I really appreciate your input. I haven't been able to dig into my Rodgers 820 power off problem because I have been snowed at my weekday job as a high school counselor. I probably won't get to it until my spring break (March 23-27). I have some other questions, though. In the keyswitch relay there's an 'orange drop.' It's a Sprague 715P 0.1+- 10% @ 1200VDC?

                        Also, as quick as I get my Rodgers back up and running, I really would like to pursue installing MIDI that works alongside the electronics. This organ has the coaxial connection present for plugging in the pipe augmentation. I don't know if this is helpful towards the MIDI goal or not? The manuals have a ribbon cable that ends on a board called time-sharing and the ribbon ties into a CMOS connection at the center of the time sharing board.

                        I'm so glad I joined the organ forum! You guys are incredible!

                        Thanks,
                        Dan
                        Dan Royster, MA, MS
                        Guidance Counselor
                        Digital Design & Engineering Counselor
                        Knight High School
                        Palmdale, CA

                        Home: Rodgers 820....I love this instrument! Has the connection for the pipe augmentation; How to get it to MIDI?
                        Church: Allen 301B (I think?) ADC....all features of an Allen ADC 4000; Would like to add MIDI to it

                        My Professional Profile: https://www.linkedin.com/profile/pub...public_profile

                        Comment


                        • #13
                          The serial pipe port probably isn't suited to MIDI. It's a serial data stream for the various pipe ranks regardless of what division is keying them. It doesn't have manual outputs, but note on/off bits for principal, flute, etc. on some predetermined sequence. On or off is determined by the installed ranks, keys pressed, and stops that are on. It's like the output from a unit organ relay to drive direct electric chests (which is exactly what it is).

                          That said, most all of Rodgers serial keying used DC at the keyswitches and parallel to serial input boards--if you are looking for MIDI out only, it's probably practical to use almost any commercial MIDI encoder.

                          Though I'm not familiar with the 820 power circuit, it's not at all uncommon to have a small value capacitor across the input power to swallow small noise glitches. The 1200 VDC is not at all an inappropriate rating for for 120 VAC circuits. Peak to peak voltage across 120 VAC can runs in the neighborhood of 400 P-P (the math isn't coming to my brain quickly), and a big cushion is useful for caps on 60 Hz circuits. The low frequency is hard on capacitors.

                          Have you gotten the technical manual from Rodgers--they are usually supportive of owners for these older models.

                          Comment


                          • #14
                            Originally posted by toodles View Post
                            That said, most all of Rodgers serial keying used DC at the keyswitches and parallel to serial input boards--if you are looking for MIDI out only, it's probably practical to use almost any commercial MIDI encoder.
                            As long as the commercial Midi encoder will work with +12vdc voltages. Most only work with +5v and even 3.3vdc.

                            Your powering off issue could be contact issues in the CPU. When you press the power on button, all of the power supply voltages must come up and the CPU start to run before the power switch is latch to stay on. If any of these are missing, the organ will power off. A friend of mine had a similar model and when I would leaned on the wood mounting racks that hold the boards, it would power down. The fix was to open the metal CPU cover and reseat the boards and push all the IC's down in their sockets.

                            Comment


                            • #15
                              The Artisan MicroMidi system will work with 12 VDC inputs; I believe the Syndyne encoders will as well.

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