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Another Yamaha C4 needs help (and so do i!)

Discussion in 'Solid State' started by Duskstalker, Oct 12, 2018.

  1. Duskstalker

    Duskstalker New Member

    Messages:
    13
    Hello,

    I've read through alot of "C4" content on this board and there is huge competence in this board to be found on that topic - so I figured it would be a good idea to ask for assistance for my C4. I believe its the north-european version (I'm located in Germany).

    I've got a C4 laying around (got stored away in the 90's and forgotten), which is in a pretty good shape (outside and inside) - but appears do be "dead"silent. I was told it was defect and when tested with a pair of headphones theres only a very slight indication of music (cd player input in both aux and tuner) with both volume and headphones volume is turned up pretty high.

    I build speakers, so im confident with the soldering iron - but I've got only a veeery basic understanding of amplifier electronics. But since the C4 often has cold solder joints I was confident I could give it a shot.

    I opened the C4 and reflew (reflowed?) the small board with the heatsinked voltage regulators and found that to be oddly satisfying - I always wanted to learn how to do small repairs and recapping on amplifiers, why not start here.

    On a side note: All 3 buttons glow yellowish on my version - and as far as i know they should actually be red / green / green. I guess there should be some colored/coloring plasticdomes on those lightbulbs?!

    The problems with my C4:

    It only puts out the slightest volume over the headphones, which made me assume something is broken in the signal way - right channel is way louder than left - which is basically dead completely.

    So, like said, I opened the C4 and it looked quite clean inside - little dust, little flux stains, no visible damage on the main boards, no bulged or defect capacitors - at first glance. I started reflowing the first little board with the heatsinked voltage regulators - it didn't solve the issue, but its only 20% of all solder points.

    Today I pulled out the headphone board because i suspected the ribbon cables, the connector on the small one was really loose.

    And there i found that alot of the capacitors on that board have corroded feet - something ive not spotted anywhere else on the board. Im pretty sure that this is number 1 culprit for the non existent audio output via headphone. this poses the question whether there actually is a problem on top of that - so i'll have to replace those first.

    To my surprise I found a readily compiled recap set for the C4 on ebay consisting of nichicon fine gold / muse - which bought instantly. So i guess ill recap that thing?! Some seem to prefer Elna on certain spots on the board, but this will have to do it for me - nich gold / muse seems pretty good.

    On these forums I found the information that I should go ahead and replace the 2SC458 transistors with the
    KSC1845FTA - i found these pieces and they're fairly cheap - but i have no idea how much of these i'll need - does anyone have a number? Do they have the same pin out as the original ones?

    Another thing would be the 2x 1n4148 diode to replace the VD1212 varisors - I found multiple parts that have that part number. What do I need? Normal or ultra fast diodes? 100mA? 150 mA? 300mA? 75V 100V? 150V?

    There is one part on that board that worries me, tho - its the 3rd big heatsinked voltage regulator between the rods for the input and phono selector switches.

    The heatsink was glued to the pcb, but ripped itself loose, solder seems ok, I'll reflow it anyway. i guess these things can die, too? are there parts to replace it, in case this regulator overheated and died? - there are signs of heat on the resistor and the "switch-rod" next to it - the resistor does measure something, but i dont know whether thats the resistance for another trace or the actual resistor.
    I tried to remove one of the rods to unscrew the heatsink, but the rod secured in 3 places - thats where i stopped today.
    I guess it would be easier to unsolder it to apply new thermal paste? Should I reglue it? Thermal resistant silicone to secure it back? Or not glue it at all and handle with care?

    I'll get my new caps sometime next week and I really hope I can make some progress with these.

    I'll happily provide pictures, but I just couldn't get some today.

    Thanks alot for reading through that wall of text and your help!
     

     

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  2. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,685
    Location:
    Fort Dodge, Iowa
    Nope --orange-green-green
     
  3. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,685
    Location:
    Fort Dodge, Iowa
    There is 8 total. But they're not the noise-prone variety. KSC1815 is an exact replacement.
     
  4. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,685
    Location:
    Fort Dodge, Iowa
    Normal There is only one kind of 1N4148.
     
  5. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,685
    Location:
    Fort Dodge, Iowa
    I use sensor safe permatex -- ultra-black
     
  6. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,685
    Location:
    Fort Dodge, Iowa
    How about connected to a power amp through speakers? Might just have an issue with the headphone amplifier.
     

     

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  7. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,685
    Location:
    Fort Dodge, Iowa
    Welcome to AK BTW..
     
  8. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,685
    Location:
    Fort Dodge, Iowa
    Usually not.required to replace. The old dried up glue is common to break loose on that pass transistor. Usually, lots of that dried glue around the other two heatsink mounted regulator pass transistors as well.
     
  9. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,685
    Location:
    Fort Dodge, Iowa
    You paid too much..If you paid more than $55 including shipping .
     
  10. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,685
    Location:
    Fort Dodge, Iowa
    This is what they all should look like.
    [​IMG]
     
  11. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,685
    Location:
    Fort Dodge, Iowa
    I've probably looked at two or three* of these control amplifiers.






    * dozen
     

     

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  12. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,685
    Location:
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    Don't hold your breath. Dirty switches are # 1. Those leaky caps are for the tone control . Pretty common issue to most of the C-4's I've worked on.
     
  13. Duskstalker

    Duskstalker New Member

    Messages:
    13
    wow, that was quick!

    thats the diode i kinda lean towards:
    http://www.produktinfo.conrad.com/d...n-DIODE_SCHALTER_75V_1N4148_TAP_DO_35_VIS.pdf
    the other one is this:
    http://www.produktinfo.conrad.com/d...62280-da-01-en-1N4148_Diode_1N4446_1N4448.pdf

    when i researched the cost for the cap replacements for the "headphone / tone board" i ended up with roughly 22€ inc vat, thats 1/3 of the amps caps. the whole set cost me 65€ inc vat - thats roughly in line with the price i'd pay if i picked them seperately. that stuff is kinda hard to come by here without buying in bulk or long shipping times and i also saved some time researching where to get which caps - time i could and should put into soldering. :naughty:

    I just inspected the lightbulbs and it seems they have been replaced already - its nice that they all work - but i guess the original light bulbs were tinted or had those color domes on them. maybe i can get some coloring domes in a model train store.

    Admittedly I've not thought about the headphone section being at fault - usually with kenwood amps the headphone output is the last thing to drop out separately - therefore i was under the illusion the "not working headphone output" of the C4 is a representation of whats wrong in the amp in general. I'll put the C4 back together in an operational state and test the pre-out outputs.
     
  14. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,685
    Location:
    Fort Dodge, Iowa
    DSC04232.JPG
    Had colored condom grommets.The yellow one is from a C-4 . The green ones for the C-4 are darker green than the one in the photo.
     
    Last edited: Oct 12, 2018
  15. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,685
    Location:
    Fort Dodge, Iowa
    This is a control amp not a power amp.
     
  16. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,685
    Location:
    Fort Dodge, Iowa

     

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  17. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,685
    Location:
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  18. Duskstalker

    Duskstalker New Member

    Messages:
    13
    thanks alot! im still waiting for my caps - i hope ill receive them tomorrow.

    the lightbulb grommets are missing the dome - maybe its a replacement or someone removed it by accident or force.
     
  19. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,685
    Location:
    Fort Dodge, Iowa
    Usually they either dry rot or someone installs the wrong size lamp and they melt.
     
  20. Duskstalker

    Duskstalker New Member

    Messages:
    13
    okay so today i found a few hours to invest into the c4, finally. i got my caps, my board holder, some color for the lightbulbs.

    so i recapped the headphone board - there were alot of dead capacitors on that board - lots of corroded feet - pretty much 80% of the bigger ones.

    i also cleaned the headphone- and the small "5 switch" board (mono, stereo control i believe) with alcohol, redid all solder points on these boards and put the boards back in.

    what i first noticed is that the volume on the headphones was increased by a good margin - still, with max volume on the main and headphone volume, it was very quiet. but far from "dead", like it was before. so i guess functionality on the headphone board is restored, mostly.

    i've come across some new issues, now since the amp puts out some music to find more.

    1. there are no "relay clicks" - when i switch it on, all i can hear is the clicking from the power switch - this aint right, right? this would also explain the low volume on the amp.

    2. big "tone control" seems to overdrive alot when fully engaged (+ max value)

    3. mute control shifts balance - when mute is enabled (lower volume) left and right channel are equally loud - when mute is off (higher volume) the right channel drops in volume.

    apart from that i can report that all switches are working, only slight noise in the big mode/input switches when input is switched. potentiometers also work, as far as i can tell, they dont hiss or drop out, no noise when turned.

    ill post some pictures later - just wanted to give a fast update and ask what i should do next.


    what i still need to do:

    recap the other boards
    reapply thermal paste
    get new fuses
    reflow the remaining boards
     

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