Marantz 250 power amp, smoked!

Discussion in 'Marantz Audio' started by grnhays, Sep 11, 2017.

  1. grnhays

    grnhays AK Subscriber Subscriber

    Messages:
    17
    Location:
    Green Bay, Wisconsin
    Turned on the stereo, only to notice smoke pouring out of my amp. I unplugged it to survey the damage, this is what I found, smh.

    Over the weekend, I took the top off to address the burnt out lights, for the meters. I took the bulbs out, and headed to the store, for replacements. Needless to say, the store did not carry them. I had to source them on line. I kept the bulbs out, not thinking there would be a problem, until the replacements arrived. Boy was I mistaken!

    Now,.... I'm pretty handy with a soldering iron. Replacing the wires for the lights, should be an easy fix. The other wires run to the back of the amp. Those shouldn't be too tough to replace, either. IMG_0829.JPG IMG_0827.JPG

    Now for the big question. Should I try to just fix my burnt wires, should I try a full recap and service bulletin upgrade, or should I try and find a fellow AK Member to rebuild the amp? I am by no means an electrical engineer. But I enjoy tinkering with things. This, is just a really expensive amp to try my tinkering skills on. Any thoughts or suggestions are appreciated.
     
  2. wlhd1610

    wlhd1610 Penny and her new friend Subscriber

    Messages:
    2,130
    Location:
    upstate new york
    They are really finicky with properly matching the predriver, drivers and outputs as indicated by the Marantz service bulletins.
    The drivers are the hard to obtain TO66 type but can be found as I prefer to use them rather than to modify them to TO220's.
    Hopefully no traces on the boards are damaged ,only wiring.
    A full recap wouldn't hurt while in there.
    Most of them are axials and the Vishay AML's work well .
    Also the small transistors are MPS type and are available still from Mouser or DigiKey.

    Bob
     
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  3. grnhays

    grnhays AK Subscriber Subscriber

    Messages:
    17
    Location:
    Green Bay, Wisconsin
    Thanks for the tips. It sounds like you've done this a time or two.

    I just got the amp. the gentleman I got the amp from said it was just serviced. I got the receipts, and a bag full of the parts. Not sure what they are? But, I'm gonna find out. Please excuse my ignorance. We all have to start somewhere.



    All the boards seem pretty accessible. On a scale of 1-10, how difficult would you say this project would be, for a beginner? I enjoy a challenge, but definately don't want to start something I can't finish.
     

    Attached Files:

  4. mbz

    mbz Well-Known Member

    Messages:
    796
    Location:
    Melbourne, Victoria
    No experiance with this amp so I maybe completely off the mark however burnt wires indicate a serious short. More wire on wire rather than a transistor
    short. Maybe have a close look at the wiring, maybe measure resistance between wires, probably need to unsolder from transformer so as not to be
    confused with transformer winding.
     
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  5. grnhays

    grnhays AK Subscriber Subscriber

    Messages:
    17
    Location:
    Green Bay, Wisconsin
    Thanks for the tip. I found a guy in southern Wisconsin, that will rebuild the amp. But,...... there is a 6 month turn around time, and a price tag of $550.

    So,...... I'm going to give it a shot. The lead time from the tech, seems a bit long. How much trouble could I possibly get myself into? It should be a good challenge. I'll update this post with the results of my rebuild, from a complete rookie.
     
  6. wlhd1610

    wlhd1610 Penny and her new friend Subscriber

    Messages:
    2,130
    Location:
    upstate new york
    I hope your guy is intimately familiar with the 250 as it is NOT a typical rebuild.

    Bob
     
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  7. Trojan4Life

    Trojan4Life Active Member

    Messages:
    377
    This really isn't an amp to learn or experiment on. It's also an amp that would be very costly to replace with an equivalent.

    There have been many factory modifications to this amp which you can do depending on your skill level. Do you know about matching transistors for hFE? Can you make a circuit to match Vce? If you know what I'm talking about, then you are no grasshopper and you are ready to proceed.

    Otherwise- send it to an expert like Bob. Or, be ready to spend 100's of hours learning, buying/collecting the parts, tools, reading all the threads on the Marantz 250 on this website and others, asking questions and waiting patiently for answers. Keep in mind that a new equivalent American made amp costs >$5000.
     
  8. grnhays

    grnhays AK Subscriber Subscriber

    Messages:
    17
    Location:
    Green Bay, Wisconsin
    I'm definitely a grasshopper, lol. I think I'm gonna leave this on to the professionals. Thanks for your input.
     
  9. ConradH

    ConradH AK Subscriber Subscriber

    Messages:
    7,118
    Location:
    Canandaigua, NY
    You need somebody with specific experience and expertise with the 250. Just being good in general isn't enough for this one. I'd try to identify exactly where the wires go and see if you can determine what failed. Could be as simple as a pinched or uninsulated wire touching something, or a really major failure.
     
    grnhays likes this.
  10. willyrover

    willyrover Super Member

    Messages:
    2,784
    Location:
    Hamilton
    If you want to do the full rebuild, go for it. But I doubt it would take much to get the amp back to the state it was in "before the fire". Removing the meter bulbs caused one of the crusty old lamp sockets to short. The wiring to the the lamps acted like a fuse - or tried to.

    The burn marks on the yellow - blue - green wires are because the lamp wires were wrapped around them.

    m250-2-c.jpg

    If the amp was working when you unplugged it, I bet it's still ok. I would unsolder (or clip) the burnt orange and green lamp wires off the tag strip. Inspect the yellow-blue-green wires and check if the burn went through the insulation. Maybe unsolder them and put some heat shrink over the damaged part. Put the amp on a dim bulb tester and fire it up. If it passes dim-bulb test, check AC voltage where the green-orange lamp wires were connected to verify that winding is ok.

    IF that unused tag on the tag strip is not connected to a transformer winding, it would be a great place to add a fuse to the lamp circuit to prevent this happening again.

    Looking at this picture, the lamp socket appears to be flapping in the breeze and the solder tags on the socket appear to be touching.

    IMG_0827.JPG
     
    Last edited: Sep 12, 2017
  11. airtime

    airtime Super Member

    Messages:
    1,950
    Location:
    Central Arizona
    If you're dropping $550 why not have an expert like Bob do it. And do it the right way. He redid my 250M and it's AMAZING !!!!!!!!!!!!

    http://audiokarma.org/forums/index.php?threads/marantz-250m-rebuild-by-bob-speece.763026/
     
  12. wlhd1610

    wlhd1610 Penny and her new friend Subscriber

    Messages:
    2,130
    Location:
    upstate new york
    It's odd that he sent you 12 output transistors back when there are only 8 to begin with.

    Also normally there is an inline fuse soldered across the terminal strip that protects the lamp circuit from that kind of failure.

    Like this all original 250 has that is in for a restoration/refurbishment:

    [​IMG]

    Bob
     
  13. grnhays

    grnhays AK Subscriber Subscriber

    Messages:
    17
    Location:
    Green Bay, Wisconsin
    Trojan4Life likes this.
  14. grnhays

    grnhays AK Subscriber Subscriber

    Messages:
    17
    Location:
    Green Bay, Wisconsin
    My 250 looks quite a bit different than that. I sent you some pics.
     
  15. airtime

    airtime Super Member

    Messages:
    1,950
    Location:
    Central Arizona
    You made a great move. I always liked the 250. But after Bob got done restoring and upgrading it, it is now my favorite amp. And I'm a TUBE GUY!!!
     
  16. grnhays

    grnhays AK Subscriber Subscriber

    Messages:
    17
    Location:
    Green Bay, Wisconsin
    I'm so excited to get this done! After the amp, I'm gonna send him a Marantz 33 preamp. That way, everything's up to snuff, and I can worry about what album I'm going to listen to next.
     
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  17. airtime

    airtime Super Member

    Messages:
    1,950
    Location:
    Central Arizona
    Did you check out the thread I posted with my rebuild? You're gonna love it !
     
  18. grnhays

    grnhays AK Subscriber Subscriber

    Messages:
    17
    Location:
    Green Bay, Wisconsin
    I read it. How was the difference from before to after? I am so looking forward to getting my 250 back, up and running
     
  19. Richs_Trains

    Richs_Trains AK Subscriber Subscriber

    Messages:
    630
    Location:
    Tucson, AZ
    Bob, Looks like my 250, I remember replacing the lamp wires with red/black. Hows the SM-7 and does this mean my 250 is reaching it's place in line? Thanks for all your great work, the 250M sounds great! Rich
     
  20. wlhd1610

    wlhd1610 Penny and her new friend Subscriber

    Messages:
    2,130
    Location:
    upstate new york
    SM7 just needs LED conversion,D.C.offset and bias final settings and then it's done.
    Your 250 is next.
    I told this fellow that his 250 should be ready by early December.

    Bob
     

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