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Working on a MC2500...

Discussion in 'McIntosh Audio' started by eiraved, Mar 27, 2018.

  1. eiraved

    eiraved Plane Whisperer Subscriber

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    I finally purchased a second MS2500 (s/n CS2719) for my garage system and figured I'd at least recap them since I don't want to move these behemoths any more once they are situated!
    I removed the lower panel and removed both preamp input/power output boards, which were extremely easy to access. I immediately saw an issue with the right channel board. The LDR401(light dependent resistor) has two of it's four legs sticking up in the air with a 470uf polarized cap soldered in it's place. The left board has all four legs properly soldered in place with no 470uf cap. Anyone has an idea why this is? Maybe some service bulletin installs this? My first instinct is to purchase another one and restore to normal, but perhaps this is an unobtainium part and the cap is a workaround.
    Also, does anyone has a service manual for the MC2500? All I could find was the schematic online. Thanks!

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    Last edited: Mar 27, 2018
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  2. damacman

    damacman Blown and Injected Subscriber

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    You bought an Mc2500 for your garage system!?!

    And I thought I was bonkers.
     
  3. eiraved

    eiraved Plane Whisperer Subscriber

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    No sir, I bought TWO MC2500's for the garage! :crazy:
     
  4. damacman

    damacman Blown and Injected Subscriber

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    ROTFLMFAO! You and @motorstereo both with insane systems in the garage!

    Have you ever seen that guy on YouTube that has a pair of MC2300s, pair of MC2500s, and pair of Sansui BA5000s in his shop powering a stack of pro speakers? I think he has you both beat!
     
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  5. eiraved

    eiraved Plane Whisperer Subscriber

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    He probably has the same issues as me with the wife. The garage is my haven and I can blast as loud as II like without repercussions. I can get pretty loud there now though with a Kenwood KR9600 I restored! I won't have to worry about her for a couple of weeks though as she's in your neck of the woods babysitting the grandkids!
    I can't wait to hear how 1000wpc sounds like...:idea:
     
  6. damacman

    damacman Blown and Injected Subscriber

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    You mean 1.3hp/channel. I'm just slightly ahead of you at 1.6hp/channel.
     
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  7. c_dk

    c_dk Addicted Member

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    Have you checked with factory parts for the multipanel service manual......

    Have no idea why the cap is there......but will need to ponder the rational someone came up with......

    35 years ago with adequate AC mains supply the 4 monos, two pair two clients, I delivered, each put out 1750 watts into our McIntosh load box.
     
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  8. Velocityboat

    Velocityboat Super Member

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    So what type of speakers are going to be blessed by those monsters. I have two of those and a pair of MC1000s. I have this vision of you blasting some U2 Joshua Tree at some Joshua Trees in the valley.
     
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  9. eiraved

    eiraved Plane Whisperer Subscriber

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    I don't have a service manual and was hoping someone here might have one available. I did look for the LDR401 online, but better chance of finding a dodo bird, LOL! I'll check with factory parts if there is no manual available here.
    Those trees are a distance from me but not much is out of earshot of the MC2500! I currently have Cornwalls III and a McIntosh XR6 pair, but can't put the brute force of the MC2500 on those if I expect them to live long, LOL! Expect an upgrade soon...
    MC1000 was a dream of mine but they're as rare as hen's teeth so I decided to stay with what I have.
    I hope to catch up to you one day...
     
  10. Velocityboat

    Velocityboat Super Member

    Messages:
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    Location:
    TX
    The cornwalls will certainly play lod and clear. The MC2500 is a great amp. I love mine. Hard to part with. You will appreciate them at any watt level. Espescially the bridged sound stage.

    The big McIntosh Amp guys on here are partial to line array type speakers. Let us know what speakers your planning to soak up those big watts. The sweet spot on those bridged MC2500s are 12 to 1100 watts. Fifty to 500 is really sweet. After power guard flashes you are back peddaing.
     
    Last edited: Mar 28, 2018
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  11. motorstereo

    motorstereo AK Subscriber Subscriber

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    Congrats to you on landing the 2nd 2500 and twin MC2500's in the man cave is the way to go:thumbsup: I hope you're able to fix the problem and get them both online; you're going to love all those Mcwatts.

    Yes same here I can go out right now in my m/c garage-listening room any time of the day or night and light up the pg lights without bothering a soul. I'd be taken out of here in a straight jacket if I ever tried that in the house after hours
    As VB mentioned now you need some big line arrays that will use and benefit from all those watts. 1000wpc on Cornwalls:eek2:
    What are you using for a preamp?
     
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  12. eiraved

    eiraved Plane Whisperer Subscriber

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    Finding this problem let me know someone's been "under the hood" so to speak! I may need to contact McIntosh parts and hope they know of a substitute.
    I laughed at this question, as I really haven't pondered the preamp issue! I have a C36, but that'll stay in my main system with the MC7150 amp and MR7083 tuner. I'll probably use the Counterpoint SA-5.1 preamp as a stopgap, or go more modern with the Anthem AVM 20. You guys have any suggestions on what Mc preamps you use which performs best with this amp?
     
  13. c_dk

    c_dk Addicted Member

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    As I suspected, but without the schematic at home could not be sure, LDR401 is part of the muting circuit. The cap was put in series with the two DC input blocking caps, which are installed minus to minus, I guess making them along with the various resistors a complicated bipolar cap.

    Why some genius installed a cap there i have no clue, a resistor or piece of wire would have made more sense but a new LDR is the correct way to go.

    The Perkner Elmer preferred replacement LDRs are long out of production and a fav of the DIY wow wow pedal camp so I would get a pair from Mac parts and replace the Clarex parts in both channels. Might look in the other amp while the system is apart and replace the muting LDRs in it also.

    There might be a replacement out there that Terry, Patrice and I have discussed but I have only tested one in MR73 application so am hesitant to recommend until some others put them into use.
     
  14. eiraved

    eiraved Plane Whisperer Subscriber

    Messages:
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    Thanks for your input c_dk! I did contact the McIntosh parts dept and they carry a replacement for the original LDR401 part number. The original part number was 144159, new part number is 144179. I placed an order for only one, because these go for $20 each (ouch!). I'll verify the manufacturer's part number once I receive it and see if I can get it for less at DigiKey or Mouser.
    However I do have a wow-wow pedal, I'll have to open her up and check...
     
  15. clinic-audio

    clinic-audio all on YAMAHA untill 1990

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  16. c_dk

    c_dk Addicted Member

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    That replacement has been available since engineering discovered that the clarix devices were failing at a alarming rate back in 1984 or so.....I believe because the LDRs contain Cadmium they were discontinued 8 or 9 years ago.

    The part should be labeled as a vactrol or vactec......and there are a number of threads on them.
     

     

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  17. eiraved

    eiraved Plane Whisperer Subscriber

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    Thanks for the link, unfortunately that Vactec costs more than what McIntosh is charging at $24.35 including 19% VAT and plus shipping from Germany.
    Good info, I'll search for those threads.
     
  18. Velocityboat

    Velocityboat Super Member

    Messages:
    1,123
    Location:
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    I have a C-39 driving my MC2500 with slider on back at 2.5 V. They canbe found relatively inexpensive and has great Synergy. The input sensitivity slider opens up lots of options. I have drivem ine with a Yamaha, Lyngdorf, and Emotiva DC-1 stealth DAC with variable inputs using the slider at lowest input. Not a complaint with any. They will sound as clean and quiet as preamp.

    As long as you have them open route the fan control wiring away from RCA input board or shield wires. That will quiet speaker hiss. The Rich Andrews mod. He posted it on AL and a remote site too. Be careful not to break fan control temp thermistor on heat sink. Plastic is too brittle pulling off inter connects on spade lugs. My mistake modding my second one. That is another 3 dollar part that will cost 20 from service.
     
  19. eiraved

    eiraved Plane Whisperer Subscriber

    Messages:
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    It appears Small Bear Electronics has a quantity of Vactec VTL5C9 for $10.50 each, half of what McIntosh charges. :D
     
  20. eiraved

    eiraved Plane Whisperer Subscriber

    Messages:
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    I saw this mod online and plan to accomplish it. Thanks for the tip on the thermistor!
    This resto will take a while to complete with work and all, but I'll try to keep you all updated.
     

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