MAC 4100

Discussion in 'McIntosh Audio' started by Scott Norton, Feb 10, 2019.

  1. Scott Norton

    Scott Norton New Member

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    I picked up a MAC 4100, serial number BY2457. I have emailed McIntosh Labs and requested the correct schematic but I'm not sure they are going to reply. The MAC 4100 seems like a nice receiver worthy of restoration. I'd appreciate any comments or assistance identifying the correct schematic and history on serial number BY2457. Thanks.
     

     

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  2. 62caddy

    62caddy Trust but verify Subscriber

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    Sorry, unable to provide a direct link. Must scroll down to MAC4100 then click on Service Manual (upper).

    http://www.berners.ch/McIntosh/en/Frame_Matrix.htm

    HTH
     
  3. mibag6

    mibag6 AK Subscriber Subscriber

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  4. Scott Norton

    Scott Norton New Member

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    Thanks for the links. Do you know if there is a way to determine when serial number BY2457 was built? Just curious... Thanks.
     
  5. 62caddy

    62caddy Trust but verify Subscriber

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    Probably not.
     
  6. eedork

    eedork Super Member

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    I recapped a MAC4100 last year and have a thread here on AK with a full Mouser parts list. Should save you some time if you're thinking of recapping it. It's a great receiver. There were a few variations of this receiver - mine was an early one, but I don't remember the exact details at the moment.

    Enjoy!

    -Matt
     

     

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  7. Scott Norton

    Scott Norton New Member

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    Hi Matt. I just read your interesting post about the speaker protection relay. My 4100 (BY2457) has a 48v coil. It is not a Magnecraft 78RCSX-11. Were you ever able to clarify the issue? Do you have a source for the correct relay? Thanks.
     
  8. Scott Norton

    Scott Norton New Member

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    Can someone confirm that MJ15003 and MJ15004 are the recommended replacement output transistors for the 4100, serial number BY2457?
    132188-132189 - MJ15003-MJ15004.png
    Also, the contacts on the speaker protection relay are badly pitted and I'd like to replace it. My relay also has a 48v coil which seems to be different than the Magnecraft 78RCSX-11 I've seem suggested on other posts. If anyone could share a source for the speaker protection relay it would be greatly appreciated. Thanks.
     
  9. eedork

    eedork Super Member

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    Hi Scott,

    Yes, I believe I resolved the issue by installing a relay with a 48V coil. I'll have to dig up my notes, but that is what I recall right now.

    -Matt
     
  10. Scott Norton

    Scott Norton New Member

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    I'm trying to resolve some problems with my recently acquired 4100. When I feed the preamp out into another amp, everything works as expected; that's the good news. The bad news is I get nothing out of the power amp output and there is no voltage on the coil on the speaker protection relay. Can someone suggest the next step I should take to begin to isolate the problem?
     
  11. MACKIE1975

    MACKIE1975 Well-Known Member

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    Hi new member

    What amp do you have?
    Check the speaker switch on your amp or preamp
     

     

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  12. Scott Norton

    Scott Norton New Member

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    I am currently feeding the preamp output of the 4100 into the line input of a Onkyo 8220. I've tried all three speaker outputs on the 4100 (and pushed in the speaker selection switch) with no luck. Any additional thoughts on the next step to isolating the problem? Thanks and I appreciate your assistance.
     
  13. MACKIE1975

    MACKIE1975 Well-Known Member

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    Check the yellow highlights
    Not sure why you still want to use the Onkyo.

    The MAC4100 is old but if it’s operating per specs then the Onkyo is not needed

    upload_2019-2-14_10-0-16.png

    upload_2019-2-14_10-0-47.png
     
  14. MACKIE1975

    MACKIE1975 Well-Known Member

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  15. mibag6

    mibag6 AK Subscriber Subscriber

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    Power off, unplugged, work all the switches and knobs full range 20-30 times and try again. I have one of those and there was no output when I first got it. Dirty switches all around. You don't mention the preout main in jumpers so make sure they're clean and connected too.
     
  16. 62caddy

    62caddy Trust but verify Subscriber

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    Keep in mind the MAC4100 uses jumpers to make the connections from the PRE OUT to the MAIN IN jacks. If you're using RCA ICs, are you connecting the cables between these jacks? I realize this is obvious but just wanted to be certain.
     

     

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  17. c_dk

    c_dk Addicted Member

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    I would guess it was built in 1979, may be early 80. Could look in my "tickler" file to see what the serial numbers were for ones I sol in '79 but.......

    The MAC4100, I believe was the best receiver ever built and even at $1500 in 1979 was the best value out there.

    It deserves a complete and thorough restoration by a restoration tech.

    With a complete tuner alighnment expect a labor cost of 7-8 hours.

    What are your goals for this unit?

    There are many threads out there highlighting the restoration of one of these or it's non tuner sibling the MA6200.
     
  18. Scott Norton

    Scott Norton New Member

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    Thanks to everyone who replied to my post. Here's the story on my newly acquired 4100:
    I picket up the receiver from a friend who had it sitting in his closet (along with a lot of other super-cool McIntosh equipment). We fired it up and it worked fine for about 2 minutes. After a few minutes of operation, the left channel power indicator pegged into the red and the speaker protection relay contacts started to glow (literally). We quickly turned the receiver off and after a few minutes we tried again with the same results. We took a closer look at the speaker protection relay (Eagle 48v) and the contacts were fried. We cleaned it up as well as we could and tried again with no change (still cut out after a couple minutes). My friend concluded that replacing the output transistors would resolve the problem (I was skeptical). In any event, I replaced the original output transistors (RCA 132188-9) with ON MJ15003-4 and now the speaker protection relay does not operate (no voltage at the coil) and I get no response from any of the 3 speaker outputs on the 4100. The preamp and associated inputs (AM, FM, Phone, etc) work fine when I route the preamp output to an external amp. I'm guessing the problem is either in the channel drivers (045219) or maybe the power supply board (045217). I am hoping someone might be able to help me identify some tests I could perform to isolate the problem. My intention is to eventually restore the 4100 but my first step is to get it working. Any assistance or advice would be greatly appreciated! Thanks.
     
  19. c_dk

    c_dk Addicted Member

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    Build yourself a dim bulb tester if you are going to probe around inside without the proper test gear.

    Expect to rebuild the power supply.

    Without a variac a dim bulb tester will allow you to compare voltages between good and bad channels even though the voltages will be low because of the limiting.

    I would be surprised that none of the resistors on the driver boards did not act as fuses when the outputs shorted.

    Sorting through the output failure will take some basic trouble shooting.

    You can monitor the input into the relay to observe what you are getting out of the amp sections. Obviously a scope would be best.
     
  20. Scott Norton

    Scott Norton New Member

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    Thanks for your reply. I was hoping there was a test I could perform with my volt-ohm meter that would isolate the problem to the power supply board or the driver board(s)? I also noticed there is no information on the schematic about the speaker protection relay (it's not even listed on the parts list). Am I missing something?
     

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