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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    I just landed an M2 and C2a. Just what I was looking for to drive my L1290's. The M2 is dusty and has evidence of being dropped (bottom panel has a warp from the inside out :eek:). Removing the top panel...sure seemed like it was the first time that had ever been done. :thumbsup:

    I had to replace bulbs and the power switch is failed closed, so I need to use a power strip temporarily.
    Sounds like those are very common issues though. I found a thread with a replacement switch from Digikey when the time comes. https://www.digikey.com/products/en?mpart=P197EESB&v=141 or I may be able to find some correct Alps switches.

    I did all of the adjustments from the service manual (idle current, power voltage, dc balance) except for level indicator.

    Deoxited the pots (hard to reach, but it's done now) and the power and speaker switches. Blew dust from the boards as best I could with keyboard cleaning duster spray. I was going to re-grease the power transistors, but I was only able to reach the transistor covers on one set. I think this is a job that will need to wait until I'm ready to disassemble for a recap. But, I was able to check some of the grease that had squeezed out of one transistor and it was still pretty fluid, not dry. I think we're OK.

    I'm a bit concerned about the OBS Toshiba power transistors. If anyone would be so kind as to share a source for authentic ones, I'd sure appreciate it. ( although I realize that's like asking a fisherman where the honey hole is ) Nothing wrong now, but I'd like to stock up before the NOS runs out.

    Also, I haven't been able to find any PN for the 22,000uF filter caps. Caps seem to be OK. During voltage tests, the caps dropped about a volt per second after shutdown. Seems OK to me, but I don't know for sure.

    Any other PM I should do to this beast?

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  2. OMGCat!

    OMGCat! AK Subscriber Subscriber

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    This is a good link
    http://marantzhallo-fi.blogspot.com/2016/12/jims-yamaha-m-2-power-amplifier-ns.html

    Really it's up to you how far you want to go. It's approaching 40 years old so a full restore wouldn't be a bad idea but they seem to be bulletproof so just touching up the various adjustments might be all you need.

    The M2 is on my list of stuff I want to get eventually. I've got a C2a to pair it to and everything.
     
  3. avionic

    avionic " Black Knights " Subscriber

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    Last edited: Feb 10, 2018
  4. stoutblock

    stoutblock If it sounds good, it is good... Subscriber

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    I ran a C-2 with an M-2 and L1290s for a while. A most excellent combination!
     
  5. 808_state

    808_state Well-Known Member

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    That power switch may unstick itself. My B-5's switch got stuck and then unstuck itself a couple months later.
     
  6. jdsalinger

    jdsalinger AK Subscriber Subscriber

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    I have to say that the switch lamp colors are ugly....but I like 'em. They have that "dawn of the PC age" look.
    I was just a pup in kindergarten when this thing was built, I guess, for me, it's a connection to a simpler time before PC's, internet and cell phones.

    Odd that Yamaha chose a tiny red LED for the C2a and the jumbo lamp-lit buttons for the C4.

    Impressive sound stage that it has, and most likely it is due in large part to the C2a, but listening to some jazz (MJQ I think) and I could sense that the drums were behind the bass. Never really experienced that with SS before.

    Thanks Avionic.
     

     

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  7. avionic

    avionic " Black Knights " Subscriber

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    C-2 was most likely meant for the B-2. M-2/M-4 C-4 and C-6 had the matching Amber and green buttons.
     
  8. avionic

    avionic " Black Knights " Subscriber

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    I don't think so. My first system was and M-4,C-6,T-1,P-750 and NS-1000.At that time. Looks counted alot to me.
     
  9. MudSlideSlim

    MudSlideSlim Well-Known Member

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    I love the M4/M2 C4/C6 lights. I think they look warm and inviting. They make nice night lights in my bedroom.
    What I detest is modern LED lights. I'm always looking for something to put in front of them as for me they are irritatingly bright
    To each his own. Anyone who restores a M2 is doing something right in my book. Keep up the good work.
     
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  10. avionic

    avionic " Black Knights " Subscriber

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    I just finished one up and have another one on the bench. DSC04162.JPG DSC04163.JPG
     
  11. jdsalinger

    jdsalinger AK Subscriber Subscriber

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    avionic, have you done a restoration thread? If so, can you post a link?
    Did you recap ALL electrolyitics? I can see you replaced the speaker terminals. What else?
    I take it you are very experienced (pro even?) But in your opinion, was it relativley easy or difficult? (seems on the easy side to me....all the boards are easily removable, which provides good access to the components.
    How delicate are the PCB traces?

    OMGCat's link is a good one, but mostly general info on the restoration.
     
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  12. avionic

    avionic " Black Knights " Subscriber

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    Nope.
     
  13. avionic

    avionic " Black Knights " Subscriber

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    Yep.All of them.
     
  14. avionic

    avionic " Black Knights " Subscriber

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    Pretty good boards.for the most part.
     
  15. avionic

    avionic " Black Knights " Subscriber

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    Easy to recap.
     
  16. jdsalinger

    jdsalinger AK Subscriber Subscriber

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    What are the odds that someone on AK would have had (at one time) the same rig that I am currently running? Small world, brother.
    And yes....in my mind, there's some synergy going on here. Both in sound and looks.

    I told my wife tonight, "If I EVER talk about selling the M2/C2, I want you to slap me". The sound is just SO wide open, detailed, black and full.
    It sounds as high quality my newly build Zen SE-84 clone. That's a compliment to both amps.
    Aside from my Fisher 500T, the M2 is the only solid state amp I've had that doesn't make me feel like I'd rather be listening to a tube amp.
     
    Last edited: Apr 6, 2018
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  17. jdsalinger

    jdsalinger AK Subscriber Subscriber

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    Well, it WAS easy to recap. I ordered the aluminum stand-off from McMaster Carr, but had to cut the male threads in half, had to order a 3/16" long standoff cause that's the required height.

    I replaced a broken power switch and the filter caps and had ordered caps for just the pre-driver and driver boards. I decided (after heating the lead on a couple of the caps on the pre-driver board) that I didn't want to dive in to that yesterday. So I buttoned it back up.

    After putting the amp back into the system, I could tell something wasn't right in the RH channel. Overall volume was down maybe 3 dB from the LH and voices seemed to be coming only from the LH channel (even though the mid-range driver was emitting sound at about the same level as the LH). It just sounded like there was a hole in the mid-range.

    I tried removing the preamp. Swapped speaker wires, swapped input wires, swapped speakers posts (A to B) and the weakness stayed with the amp.

    So, I decided that I must have overheated a cap, or didn't resolder sufficiently after I heated up the lead (never had issues with the two previous amps that I recapped). I realized that I now had to do the full driver board recap ( I'm OCD and knew I wasn't going to sleep well until it was done ). I didn't test after each cap ( shame on me ) because I figured only 4 caps...what could go wrong?

    Well, after the recap, there is a snappy buzz in both, but louder in the RH. Had been dead quiet before. :( The buzz seems to be louder when I first turn on the amp and then quiets down after I play some music (or maybe that's just cause I'm in my listening position). It is quiet enough that any music played easily drowns out the buzz, but something just ain't right.

    It's definitely a 120 Hz buzz, judging by the tone and the fact that it's not coming just through the woofers. I'm researching possible causes, but what I'm finding so far is that typically 120Hz comes from filter caps. I'm considering putting the original filter caps back in to see if that has any affect.

    Aside from the buzz, the sound quality is excellent.
     
    Last edited: May 20, 2018
  18. zaibatsu

    zaibatsu Well-Known Member

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    Was the volume reduced RH channel fixed, or are there two different problems now?

    I think it would be useful to show some pictures of your work, some details about the parts you used, and particularly some information / pics of the mail filter cap mounting - eg. match original pinout or needed to fab something?

    It does sound like you may have just dislodged a connector / broken an earth connection somewhere, but a few different sets of eyes glancing over things can help. It's worth double checking wiring, connections can break when you move the boards. I find having meter in continuity mode (or resistance mode, <0.5Ω = good) and probing either side of suspect wires with the amp switched off works well.

    Just some ideas since avionic / others haven't chimed in yet.
     
  19. Dr. Ear

    Dr. Ear Well-Known Member

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    Check polarity of the caps you have replaced.
     
  20. OnTheBlitz

    OnTheBlitz Say Hello to Knucklehead & Scoots :-) Subscriber

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    Look for interconnect problems from board to board before going backwards and installing the old caps. If all soldering on the new caps is good, then it is likely a connection problem. Also, you may have inadvertently heated up adjacent solder joints on other components near the caps you replaced, may want to inspect for that and make sure none are cold.

    Good luck. That is a nice amp.
     

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