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Thread: Help elder Dad reconnect Model C26, MR71, SE402 and LX5

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    Help elder Dad reconnect Model C26, MR71, SE402 and LX5

    In the 1970's my Dad purchased purchase a McIntosh system comprised of Thoren turntable, Model C26 preamp, Mode MR71 FM Tuner, SE 402 Amplifier and LX5 speakers. He enjoyed the system until the 1990s and then lost interest which lead to the system being disassembled. Now in 2016 I am attempting to reactivate the entire system so he can drift off and listen to his favorite Big Band music and bring a big smile to his face. My challenge is the wiring sequence between the SE402 and the LX5. On the attached diagram do I have the right connection points? In addition, in the orange circles you can see Black and Red solid core wire that is routed through some drill holes. The SE402 is mounted in the same speaker cabinet with these drilled holes and red and black wires pulled through. What I am supposed to do with these? Really appreciate any guidance that might be shared. Thanks in advance.
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    Senior Member grumpy's Avatar
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    This nominally looks right, although I can't see if the C26 MAIN output is duplicated where you have the gray cables plugged in.

    Regarding the "extra" wires, I expect that was just an internal version of what you've shown on the one cabinet that has both
    an LX5 crossover (not the speaker model) and the SE402... so you would not need both paths connected (SE402 to LX5) in parallel.
    If concerned, you could certainly disconnect the wires coming through the drilled holes (between SE402 and LX5 input) and run
    your own.

    The speaker load is likely to be the S7, consisting of an LE15A low-frequency, and an LE85 driver with HL91 lens/horn, could
    be one of several systems. Pictures of the front/back would help

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    Senior Member grumpy's Avatar
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    Any luck firing that all up?

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    Interim Challenge

    Quote Originally Posted by grumpy View Post
    Any luck firing that all up?
    First off Grumpy we really appreciate your guidance. Last night was my first time back to my parents house and we fired up the system. No sound. Started working my way backwards and found the SE402 BUSS GMQ 1-1/4 fuse was blown. Ordered one last night on Amazon and will attempt again next week. The wiring of the components appears to be straight forward. I don't know if sub components on the tube based AM/FM tunner, or the SE402 have a proclivity to misbehaving after sitting idle for 30 years. Capacitors losing their capacity capabilities, etc. Not going to give up until this system is blasting the 1812 Overture! We will continue to update you with our failure or success and hopefully you will continue to share your wisdom. Thanks again.

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    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by WirelessGuy View Post
    First off Grumpy we really appreciate your guidance. Last night was my first time back to my parents house and we fired up the system. No sound. Started working my way backwards and found the SE402 BUSS GMQ 1-1/4 fuse was blown. Ordered one last night on Amazon and will attempt again next week. The wiring of the components appears to be straight forward. I don't know if sub components on the tube based AM/FM tunner, or the SE402 have a proclivity to misbehaving after sitting idle for 30 years. Capacitors losing their capacity capabilities, etc. Not going to give up until this system is blasting the 1812 Overture! We will continue to update you with our failure or success and hopefully you will continue to share your wisdom. Thanks again.
    I wouldn't blast anything right away... many parts could have issues and might be damaged.

    After replacing the fuse(s) if you still have to sound you might bypass the SE402s and try an outboard amp... any basic power amp or integrated should work. Also, if Grumpy is right and the system is using LE15As (I also suspect this is the case.) These will likely have the old yellowish surrounds that become rock hard over the years. Powering these up at higher levels will crack them. The surrounds will need to be replaced. If the LE15As are a bit newer and have gray foam surrounds, these will likely have crumbled and powering them up will definitely ruin the woofers.

    With a little care and patience you should be able to get the old system singing again.

    Good Luck!


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    Yes, before you start playing anything at any volume other than a low signal just to check, you'll have to check out EVERYTHING, to be safe. Having the system in storage or sleeping for the last 30 years isn't terribly uncommon, but a lot of the gear will have some issues, mechanically, electronically, and reliability wise.

    You'll need to give us some pictures of the JBL speakers in question, external with and without the grilles on. That will give us some idea of the condition of the woofers, and what other components you have in there.

    As mentioned, the LE15a woofers will have white (now yellowed) surround rings attached to the cone and frame that have likely stiffened/hardened over time - they do this. The woofer will have restricted movement and any moderate volume will damage the surrounds, plus put extra strain on the amp and voice coil if you try to increase the volume - that will only heat the voice coil beyond its ability.

    The woofers can be successfully re-foamed or resurrounded, but you need a good shop. Orange County Speaker Repair is now closed, so the best local shop may be Upland Loudspeaker Service. We can help you get in touch with them.

    The LE85 horn driver is likely to be ok unless some damage through excessively loud music or amp fault occurred.

    As for the SE402 energizer, the unit is quite old and very hard to tell if it will be reliable in the short or long term. Having it looked over may be important, and replacing components like capacitors is likely needed. Even if it fires up with a new fuse, there is no telling if it will work for long. I would recommend Tom Ishimoto at Northridge Electronics for the technical work. Same for any work on the McIntosh gear.

    I can provide help for getting the Thorens up and running, depending on which model it is, and what cartridge is there.

    Also, you may want to consider while the gear is out (speakers first), you can have a running system for your father's enjoyment if you want a loaner system. Many of us are in the SoCal area, and have plenty of spare gear (amplifiers, speakers, etc.) that you could use while the gear is getting repaired. then you can have your original system back up and running.

    Let us know how to help.
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    You may have to order a few fuses, those are slow blow, size restricted fuses, and the amp is a germanium transistor amp (very early semiconductor devices which quickly were replaced by the now common silicon transistors since the late 60's-early 70's).

    http://www.audioheritage.org/vbullet...roubleshooting

    The later SE400/408S service manual, which is later and somewhat similar, and uses silicon devices. Might provide some hookup instructions.

    http://www.jblproservice.com/pdf/Vin...00S_SE408S.pdf
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    When faced with another JBL find, Good mech986 says , JBL Fan mech986 says

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    Require Troubleshooter that does House Calls.

    Basically Dad is going to feel more comfortable having someone that has experience working on his system. I am checking to see if anyone has a referral near Northridge, CA that can schedule a paid visit to a home to begin the process of identifying and fixing what needs to be repaired.

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