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Rodgers Glasgow 740B issues

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  • Rodgers Glasgow 740B issues

    Hey all,
    Recently aquired a 740b for church use. Had it for about 3 weeks in service, and issues are now beginning to dpring up. Please help identify the cause and the fix..

    1. Pedal lights and music rack lights quit. I have checked fuses and nothing blew, nor are the bulbs in the rack blown but one of the pedal lights are rather black in the glass. This soecific bulb also kept getting brighter and brighter like it was being overpowered, in which simply tapping against it would return it to normal brightness. The lithts quit when it became brighter than usual, so I smacked next to it, which then all the lights quit (no not the control led’s, just ped and rack). Upon removing the lights from the pedal sockets, I discovered that the board which contained the “metal support clips” for our over-heating light is rather crisp and brown behind where the light bulb was. Thoughts?

    2. After rhe organ is on for a good few minutes, ocasionally a faint hum will begin and get louder and louder until a faint popping sound marks the end of the humming and all is sulenr again. Does this hint at a power supply issue? On another note, we have 4 m10 speakers installed on this organ. As we have retired our essex 640 with a similar (if not idwntical) power supply, would it be practical to incorperate this power supply into the 740 as well mearly as an extra amplifier to reduce the stress from being on one amplifier? (I.e. 2 m10’s and sub on one amp, and 2 m10’s on another).

    3. The lower first octave of the trompette likes to crackle ans even loose all treble. This is fixed by gently wiggling the computer board with the main reed treble controls which is attatched to the main reed keyer board by “molex clips”. Would it be safe to assume this is simply a cold solder joint?

    Finally, 4. The piano filter makes a noticable hum as iff all the keys were sounding at once when the piano is activated. However when the harpsichord is activated, the piano humming stops. I’m really not concerned about fixing that as the piano is useless, but any ideas what that xould be? If this was a Conn 652, I’d describe it as a multiplexer issue.

    Let me know thoughts, forvive poor typing, I am posting this frantically from my phone. Thanks and happy thanksgiving!
    Richie

  • #2
    1. It seems like the pedal light was too high of a wattage or the wrong bulb voltage to burn the circuit board. It may have damaged the power supply.

    2. You could swap power supplies if they are the same part number--in that case they would be identical.

    3. The daughter board on the Trompette has the individual filters. It could be cold solder joints, or just bad connections. Unplugging it and plugging it back in will held clean the contacts. If in moving, the solder joints fractured, they will need to be resoldered.

    4. Piano and Harpsichord are the same keying circuit, just different filters used alternately (i.e., when Harpsi is on, Piano is off). Mavbe some of the piano filters are adjusted poorly--almost or into oscillation.

    If you have a Rodgers technician, get a service call. It will get fixed faster by someone who is familiar with the organs design.

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    • #3
      Looks like the fuses for the lamp voltages are Pico Fuses (see: https://www.littelfuse.com/industrie...ico-fuses.aspx) soldered onto the power supply board. You can check to see if they are blown with an Ohm meter with the power off.

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      • #4
        We just serviced a 740 with a hum/noise/popping issue after warmup. We fixed it (crossing my fingers anyway) by pulling the 3-channel amplifier board loose and then snugging it back in place. It is connected to a row of power transistors, which are mounted on the central heatsink, with plug-in connections. These spring-loaded plug-in connectors are certainly subject to getting a bit intermittent after 35 or 40 years, and just the act of gently unplugging/replugging seems to have fixed the problem. We also "exercised" the thumbwheel pots on the output board at the same time, though I tend to think the noise was coming from the power transistor connections.

        I don't know how you could easily go about paralleling the two amps in one organ. You can of course add standard Rodgers S-100 amps to that model with Rodgers 5-pin cables plugged to the output board. I'm not sure that's a problem though, as I've seen many installations where two M10 speakers were driven by a single channel of the built-in amplifier. It seems to be a pretty sturdy amp.

        Yes, pico fuses. I hate those things. Cannot imagine why in the world they were ever invented or why Rodgers would've used them on a big hefty power supply chassis! I have replaced them with ordinary fuses by soldering a fuse holder on wire leads directly to the stubs of the picos.

        The lamp power is 24 volts and the lamps are all 12 volt, thus the pedal lights, like the pairs of desk lights, are in series. One going out kills them both. But, as toodles points out, when the weird one was coming and going and possibly shorting out, it may have damaged the power supply. Or blew a pico fuse.

        BTW, the pedal lamp assembly is, IMHO, quite shoddy. I have always hated that wire screen cover that you have to deal with to get to the lamps. I suppose it's there to protect the legs of the organist if the lamp should blow up or shatter. But you must be VERY careful when re-mounting it not to short out the lamp clips!
        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

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