Yamaha M2

Discussion in 'Yamaha' started by jdsalinger, Feb 10, 2018.

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  1. jdsalinger

    jdsalinger AK Subscriber Subscriber

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    Thanks for all the advice guys!

    The reduced volume issue seems to have been fixed. Even with the new buzz, vocals and instruments seemed to be more balanced.

    I didn't have to really fab anything for the main filter caps except for the standoff.

    I DO have a meter with continuity mode. So, I will dig in and anyalyze more with that.

    I checked the solder joints of all the new caps and they are identical to the original joints. Not shiny, but they don't appear cold. They appear to be solid and I also verified continuity of all leads to adjacent components on the same trace.

    These boards are really stout. I don't think I overheated anything and certainly didn't overheat traces. So, I'm fairly confident there (unless there's something else I need to check).

    Thank you. As for polarity, just to confirm....all of the negatives have a solid block printed on the top side of the board to indicate neg, correct? That is how I installed them. (also referred to how the original cap was installed, but it's possible to make a mistake).

    At one point, I panic'd thinking I had installed the filter caps wrong, but brown wires are positive and blue wires are negative .

    I did reinstall the original filter caps and that had no affect.

    I think you guys are correct that perhaps I broke a connection loose when moving the boards around. The multi-color harnesses with the white connectors are very tight until you snip the zip ties holding them to the main harnesses.
    Although the connectors probably got pulled a bit, I don't see any evidence of broken solder joints. I was very careful not to overheat. I think I had the iron on at the right temp and was holding the cap on the other side of the board as I soldered.
    Never got too hot.

    Would a board-mount transistor cause a buzz, or are we pretty sure that I'm chasing a bad ground?


    I will try to post some pics tonight.

    One more thing I noticed, why does the LH pre-driver board have a safety cap from the B+ to ground and not the RH board?
     

     

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  2. zaibatsu

    zaibatsu Well-Known Member

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    I'd check all wiring connections you might have moved, usually the ones where the wire is soldered to the board via a solder terminal are the ones the wire can just snap off. Sometimes it's an intermittent break which is where the resistance checking with meter can help. Connectors are usually OK but I unplug/replug them all just to make sure. It's also worth inspecting solder joints of all transistors (and any power resistors) on the boards you moved, and retouch any bad ones.

    I doubt your new solder joints are a problem, a good one will live longer but pretty well any joint will conduct just fine for a while. I doubt overheating anything is the problem either. More likely that you've either bumped a component that had cold joints, or moved some wiring that was just hanging on (pretty common).

    It's also worth making sure all screws are done up and none missing, some can be responsible for earthing.
    Since the amp is still working and coming out of protection, it'll just be something minor, take your time.

    Sometimes the silkscreening is wrong so it's best to always check the orientation of what came out of the amp, but it's rare so you'd have to be unlucky, especially if you were vaguely conscious of it. These days I take a "before" photo before starting so I have a reference for factory orientation.
     
  3. avionic

    avionic " Black Knights " Subscriber

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    True.. But !! Not always correct.
     
  4. avionic

    avionic " Black Knights " Subscriber

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    Concur..
     
  5. avionic

    avionic " Black Knights " Subscriber

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    I'm not aware of any misprints in the M-2. But .. I always check the orientation of what came out of the amp, So I may have not noticed a misprint. As I install the new part with the same orientation as the removed old part..
     
  6. avionic

    avionic " Black Knights " Subscriber

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    The molex connector with the red yellow and blue wires is very easily damaged if your not very careful. It connects to the pre-drive sheet ( +100,-100,LP ) .. This will cause issues with the protection circuit. To fix if it is fouled up. I just hard wire the wires directly to the circuit board after removing the connector plug and socket.
    The part that gets damaged is the female part of the connector.
     
    Last edited: May 21, 2018

     

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  7. OMGCat!

    OMGCat! AK Subscriber Subscriber

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    When I go through a device to check what caps I need to order I always mark the top with a line going forward from the center to the edge.
    This tells me I counted the cap in my parts list and also will help if I question which way it came out.

    Not saying this is what happened to you, just a trick I like.
     
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  8. jdsalinger

    jdsalinger AK Subscriber Subscriber

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    I'm eliminating possibilities, but no root cause yet. I verified continuity on all of the umbilical ribbon cables from pre-driver to driver and from pre-driver to meter board.
    All had continuity. The one thing I am not sure about is the polarity of all my caps. Basically, all of the negatives are pointing the same direction (up when the board is flopped down for work).
    The two 100/10 don't share a negative, but that checks out with both the board and the schematic. (And I'm about 95% certain that that is how they came out)
    I can upload some soldering pics I took, but I figure that is a moot point since there is continuity and no evidence of a cold joint on any of them.

    Is it possible I zapped one of the transistors or would that result in NO sound?

    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
     
  9. avionic

    avionic " Black Knights " Subscriber

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    [​IMG]


    I am seeing green oxidation on that component ( jumper wire,diode ,resistor ) right next to the top e-cap. That dried glue around those heatsinks really needs to disappear. Any metallic parts in contact with that glue needs to be inspected for corrosion damage.
     
  10. Bratwurst7s

    Bratwurst7s In The Frying Pan Subscriber

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    Also, in the last photo of post #28, the jumper between the upper heat sink and the FG cap looks corroded on the lower end. Damn SonyBond.

    Cheers,
    James
     
  11. jdsalinger

    jdsalinger AK Subscriber Subscriber

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    Noted. I will inspect. Danke Schoen !
     
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  12. avionic

    avionic " Black Knights " Subscriber

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    Bitte schoen..
     
  13. jdsalinger

    jdsalinger AK Subscriber Subscriber

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    Thanks to the photos on the link that OMGCat! posted, I can tell that my caps are in the same orientation as the ones shown on that restoration page.

    I think I may get a chopstick and lightly tap some components to see if I can get the buzz to go away. Aside from that, I'm kind of running out of ideas.

    Probably will do that Saturday morning along with cleaning off the glue and inspecting jumper continuity.
     
  14. jdsalinger

    jdsalinger AK Subscriber Subscriber

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    Well....:crazy::dunno:
    I was planning on a long troubleshooting session today. I powered her up expecting to hear the dreadful buzz saw sound and.....nothing. It was SO dead quiet. Not even a mechanical hum.
    I thought surely now the relays are not kicking in and now something REALLY serious is wong. But plugging in my iphone, I got sweet music with a totally black background.

    I was tempted to just carefully button it up, but thought that as long as I had it open, I should wiggle some wires and tap on caps to see if I could induce it again. Tried that and nothing.
    Caps seem very solidly mounted and flipping the amp board/heat sink assembly a couple of times didn't recreate the buzz.

    So, now she's running tunes in the basement and breaking in the new caps. Such wonderful detail. Bass on CSN "Long Time Gone" is warm and room-filling.
    No perceptible imbalance issues or "holes" in the midrange. Can't wait for tonight's listening session.:music: Thanks again, Yamaha brothers.

    Just in time for the long holiday weekend!!
     
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  15. avionic

    avionic " Black Knights " Subscriber

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    Super..:thumbsup:..Flourescent or CFL lamps can cause buzzes/humms ..
     
  16. jdsalinger

    jdsalinger AK Subscriber Subscriber

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    Yes. And smart TV's too, I've discovered. Had a tube amp that I replaced filter caps only to discover it was the TV. :rolleyes:

    There is a smart TV and CFL in the room, but I don't think these were the issue.
    Probably have a broken something, but I'll let sleeping dogs lie just for now.
     
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  17. jdsalinger

    jdsalinger AK Subscriber Subscriber

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    The C2a is now recapped as of this morning. :beerchug:
    I was really pleased with how easy it was. Touched up several cold factory joints too. Didnt do the MC preamp though since I use HOMC &. MM carts.
    Not sure if lytics need to break in but I’m letting it run till tonight’s session.
     
    Last edited: Jun 9, 2018
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  18. milo63

    milo63 AK Subscriber Subscriber

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    I've got a M-2a that needs love as well, hesitant to dive into a rare/valuable unit.
    Did you get a parts list from somewhere or make your own?
     
  19. avionic

    avionic " Black Knights " Subscriber

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    Like to see a photo of that...:biggrin:
     
  20. milo63

    milo63 AK Subscriber Subscriber

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    :(
    My bad....
     
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