C-70 Preamp - Great deal because of this...

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

  1. Electone

    Electone Well-Known Member

    Messages:
    705
    Location:
    London, Ontario, Canada
    Corner damaged. Nothing broken, plastic piece is intact, cover is bowed out, faceplate bent in.

    [​IMG][/IMG] [​IMG]
    [​IMG]
    Looking for opinions on the repair of the faceplate. My thinking is some heat, a flat surface and some good whacks by some sort of blunt instrument. Thoughts please...!
     
  2. OMGCat!

    OMGCat! AK Subscriber Subscriber

    Messages:
    2,166
    Location:
    San Diego, CA
    I've worked out aluminum with two blocks of plastic and a hammer. I was two for two with shipping damage a while back and had to make the best out of it.

    One dolly needs to go on a hard surface and the other goes on the other side of the work.
    You then just tap away with the hammer while you work the corner back into shape. It will take a lot less than you think. It's also a lot easier if you can get someone to keep hold of the work while you manipulate the hammer and plastic dolly.
    Big things to watch are keeping the dollys clean. If they stay clean and you are careful you shouldn't scratch the face. If you get dirt in between you will definitely scratch it. A layer of masking tape can also help with this.
     
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  3. Electone

    Electone Well-Known Member

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    705
    Location:
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    Looks like I'm going out to get some plastic dollies and a nice mallet.
     
  4. Bratwurst7s

    Bratwurst7s In The Frying Pan Subscriber

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    Another option that has worked well for me is a couple pieces of (very) clean hard pvc and a bench vise. It works pretty well for at least getting things close with no impacts and then some tapping with the plastic and hammer to finish things off.

    Cheers,
    James
     
  5. N8Nagel

    N8Nagel AK Subscriber Subscriber

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    Am thinking plastic cutting boards may work in a pinch for this, just cut one up on the bandsaw...

    Second using masking tape to protect
     
  6. avionic

    avionic " Black Knights " Subscriber

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    38,105
    Location:
    Fort Dodge, Iowa
    All else fails ... Find and parts unit..
     
  7. Electone

    Electone Well-Known Member

    Messages:
    705
    Location:
    London, Ontario, Canada
    No fun in that... :)
     
  8. Electone

    Electone Well-Known Member

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    705
    Location:
    London, Ontario, Canada
    The wife has already been informed that there could be some dents in her favorite Ikea boards...
     
  9. Blue Shadow

    Blue Shadow I gotta get me a new title

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    SE PA
    I have a workbench with a sheet of vinyl flooring on it that provides one excellent hard flat surface to accept metal getting bent back in shape. The vinyl provides a bit of give before the hardwood bench stops the metal from moving. Easy to get things bent back right, start with easy hits to get an idea of how much force to use, use that force and taper back down to low force hits as you fine tune the repair.
     
  10. pfcs49

    pfcs49 Phil Subscriber

    Messages:
    1,966
    Location:
    N/W NJ, USA
    A 6-8" adjustable end wrench with something to protect the outer surface of the amp-thin and relatively un-compressable. (no nicks in the jaws!)
    Tighten the jaws fully, start at the edge/beginning of the bend, tweak it straight, pull off the wrench and inspect. You want to get almost all of the bend out of the area covered, then move in a little and tweak that. You will see how the inner part (away from the jaws) of the bend, also straightens, following the area near the jaws. It's kind of intuitive, but if you have an eye for this, you'll get it remarkably straight with little or no signs of what was.
     
  11. Electone

    Electone Well-Known Member

    Messages:
    705
    Location:
    London, Ontario, Canada
    What's the general consensus on the use of some heat (heat gun, hair dryer)?
     
  12. pfcs49

    pfcs49 Phil Subscriber

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    Location:
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    IMO a bad plan. First, because aluminum is a great conductor of heat, most of the face would get very hot using a heat gun. I don't know what it might do to the finish.
    I've never needed heat to straighten aluminum.
     
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  13. Electone

    Electone Well-Known Member

    Messages:
    705
    Location:
    London, Ontario, Canada
    Bloody channel imbalance :thumbsdown:. Cleaned the hell out of all switches and pots. Eventually started tapping on the board with the back of a screwdriver - click <off>. Whack again, click <on>. All solder joints are good - I re-did any suspicious ones. These Yamahas were completely controlled by relays. There are eight identical mini-relays that do just about everything. I've read through the forums - looks like they're unobtainium. So, off they all came - Deoxit on construction paper, cleaned the contacts. Lots of black crap came off. Re-soldered them all back in place and holy hell, channel imbalance gone :banana:. Now when you whack on the board, no more click off. We'll see how long it lasts.

    The C-70 is a beautifully made piece. No fancy caps like in later Yammy pre-amps, but a full recap will be in order soon. Parametric tone controls are an added bonus. No variable loudness or any loudness whatsoever on this unit.
     
  14. avionic

    avionic " Black Knights " Subscriber

    Messages:
    38,105
    Location:
    Fort Dodge, Iowa
    Not quite.. But a set of 8 will cost $100.
     
  15. avionic

    avionic " Black Knights " Subscriber

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    38,105
    Location:
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    So how did the metal work pan out ?
     
  16. Electone

    Electone Well-Known Member

    Messages:
    705
    Location:
    London, Ontario, Canada
    Yeah, not a whole lot of selection out there. Part is HB2YD-DC24V by Matsushita. Going to scrounge around and see if there are any close replacements. I've bent pins to get relays in before. It may not look pretty, but it works.

    Not bad. I'd say I got 90% of the bend out before metal stress started setting in. Will post a pic soon.
     
  17. avionic

    avionic " Black Knights " Subscriber

    Messages:
    38,105
    Location:
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    I know exactly what the part number is. There around $14 each individually.
     
  18. Electone

    Electone Well-Known Member

    Messages:
    705
    Location:
    London, Ontario, Canada
    Thanks, but not going to burn $112 for a unit I'll probably end up flipping. Was hoping for some cheap Chinese knockoff once the De-oxit fix wears out (which it will).
     
  19. avionic

    avionic " Black Knights " Subscriber

    Messages:
    38,105
    Location:
    Fort Dodge, Iowa
    Complete set of new relays..
     
  20. Electone

    Electone Well-Known Member

    Messages:
    705
    Location:
    London, Ontario, Canada
    Man, that muting relay is probably the most irritating in the unit. When it's wonky, throws the whole audio out of whack. Cleaning and burnishing did nothing. Worn contacts. Solution - jam some folded paper between the mute-off contacts. No mute control anymore, but never use that anyways. Singing happily now. Photo of corner repair:

    [​IMG]
    Not perfect, but acceptable.
     

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