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Yamaha M-45 - Help needed

Discussion in 'Yamaha' started by Bastian, Oct 2, 2018.

  1. Bastian

    Bastian New Member

    Messages:
    16
    Hello Everyone.

    I am more of a DYI, hobbyist, but very much after the music rather than a proper technician. However, I have in the past effectively recapped couple old units for the sake of it, changed resistors to fix hiss, and never faced significant issues.
    Now, to the point. I have a Yamaha M-45, which happens to be my favourite current unit. Might be synergy with other components? I don't know. Anyways! I decided to take preventive measures as it is getting old and, well, went in for a recap during some days off I had, cleaning volume pots, etc. Got a pair of 22000 uf / 80 V Nichicon KG to replace the big caps from Mouser, Canada. I took the old ones out while looking at the soldering side of board carefully taking the tin out.
    To my surprise when I looked at the other side of the amplifier there were no signals for what should be the positive or the negative for these big caps. I said, No problem! and went to look into the pictures I always take to review anything. Now, the sets were different and the pixels were downsized on the camera, unreadable pictures in other words. I then went to read schematics and check the thing, I thought had it all figured out, turned up the amp and blew the fuse instantaneously. Honestly, I checked everything. Nothing else could have gone wrong (as if this is not already a major issue) but the polarity of these caps. Can anyone offer a hand? (By the way, I have used Wire soldered to the flat leads of the Nichicons. Then I sent the wire through the holes and soldered to the board eyelets in a substantial way. The weight of the main filter caps is being supported by the plastic bracing that comes with the amp. )

    Let's start with this... how should the main filter capacitors be placed then? On the schematics, they come as C172 and C171. However, on the circuit map, they would not show. Looking at the front of the unit, I assumed C172 would be the right Cap, as the + side shows connected directly to Q147 and Q148. So the final positioning would be right cap (C172) positive towards me, and negative towards the back of the unit. Left cap (C171) would be Negative towards me, and positive towards the back of the Unit. This looks like is probably very wrong. A little help here will be amazing. That... if turning the main caps to where they should be and replacing the fuse would bring the amp back and I did not kill it altogether.
    Another thing... should I plug speakers to turn the unit on for this kind of amplifier? I did have nothing plugged to it. Might that be it? I will follow advise and if this does not work, I will advise back and we will go from there.
    Thank you for the help to everyone beforehand!
     
    Last edited: Oct 2, 2018

     

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  2. avionic

    avionic " Black Knights " Subscriber

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    C171 positive lug goes to D136 + lead
    C172 negative lug goes to D136 - lead
    And of course, the negative of C171 and positive of C172 are linked together ie ground

    Look at the copper foil side of the board to determine which lug goes to which rectifier lead.

    D136 is the bridged rectifier behind the two main caps. The + and - should be labeled on the top or sides of the rectifier.
     
    Last edited: Oct 2, 2018
  3. avionic

    avionic " Black Knights " Subscriber

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    Welcome to AK btw.
     
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  4. avionic

    avionic " Black Knights " Subscriber

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    C171's mounting location is the lower connections in this photo.. Note: the copper trace + of rectifier D136 ---> J574(jumper wire) to main cap C171 positive connection.

    Red is Positive and black is negative main cap connections.


    upload_2018-10-2_20-52-4.png
     
    Last edited: Oct 2, 2018
  5. Bastian

    Bastian New Member

    Messages:
    16
    Thank you for your time and help Avionic. Its deeply appreciated. Fantastic! I can see the mistake clearly here. Well, I got the numbers right, but the polarities wrong! I placed them backwards!!!

    I will flip them and replace the cap some time this week. Will let you know if the amp is still alive... I hope it is!
     
  6. avionic

    avionic " Black Knights " Subscriber

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    That will pop a fuse in a nanosecond.
     

     

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  7. Bastian

    Bastian New Member

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    Hi Avionic. I replied yesterday as per the reading, and I thought I had them backwards. No, I didn't. I regarded 171 as 172 and viceversa. However, they are properly placed.

    I removed them before even checking. I had them all good. Please see this picture. I soldered them again, and as soon as I try to turn it on it just blows the fuse immediately.

    20181003_220426.jpg


    What else could it be. I didn't change anything but the metal oxide resistors and the caps. I checked every single one of them, all looks ok.

    I killed my amp trying to help it. No idea what could have happened.

    What is the effect of connecting two caps going positive?
     
    Last edited: Oct 3, 2018
  8. avionic

    avionic " Black Knights " Subscriber

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    Remove D136 bridged rectifier and check it like 4 diodes out of circuit.
     
  9. avionic

    avionic " Black Knights " Subscriber

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    Post a good clear photo of your solder artwork. Look for possible solder bridges around all your new solder connections.
     
  10. avionic

    avionic " Black Knights " Subscriber

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    Until you get this power supply squared away. No speakers and no input. Build yourself a dim bulb tester.
     
  11. Bastian

    Bastian New Member

    Messages:
    16
    Removed D136 and All readings were 4.94 to 5.04v; however, one side gives 0.0 both ways. I'll upload pictures as soon as I get them edited.


    The big filter caps were solidly soldered. Due to the removal it looks now sloppy. No bridges that I could see at all. I decided to use WIMA film caps for lower uf values. Placed the negative side of these based on the lead with a "-" symbol assuming its the negative side.

    All other caps are properly placed in negative. I lifted some of the circuit on the C127/128 (stupid glue), thus the white board exposed and the blob of tin as I scratched some of the copper to make a new soldering point.

    I have looked for bridges or left overs that fell somewhere. Nothing I can see.

    20181004_005141.jpg
     
    Last edited: Oct 4, 2018
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  12. Bastian

    Bastian New Member

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    More pictures

    20181004_011504.jpg 20181004_011435.jpg 20181004_011426.jpg
     
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  13. Bastian

    Bastian New Member

    Messages:
    16
    D136, Readings:

    20181004_072343.jpg

    I guess one side is gone, this means that it needs to get replaced? I will be checking how much for it. Let me know if I should place an order for it, and what could be a reliable source. It shows discontinued. Also, Honest opinion, would it be possible that many many more parts got capped out due to this?

    Many thanks again Avionic!
     
    Last edited: Oct 4, 2018
  14. avionic

    avionic " Black Knights " Subscriber

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    Mouser Electronics
     
    Last edited: Oct 4, 2018
  15. avionic

    avionic " Black Knights " Subscriber

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  16. avionic

    avionic " Black Knights " Subscriber

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    Anything is possible . But I really doubt it.
     

     

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  17. avionic

    avionic " Black Knights " Subscriber

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    Your boards look fine.:thumbsup:
     
  18. petehall347

    petehall347 the brandy coffee man Subscriber

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    comparing you pic to the manuals pic yours look reversed .. + is on top left whichever way round the board is . you have top left as negative . unless the manual is looking from underneath that is .
     
  19. avionic

    avionic " Black Knights " Subscriber

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    The manual illustration is the foil side. Which is stated at the top left of the illustration.A typical Yamaha illustration.
     
  20. Guest125

    Guest125 Active Member

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