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Fixing an old CK2III

  1. suicidal_orange
    After all the below I fitted a replacement opamp and all measured well so I plugged in some KSC75 for the real test.  The left side was quieter but other than that all seemed well - I continued to listen while poking the connections expecting one to be loose (the RCAs were the worst I've ever used and I thought single core wire would be easier to route...) 
     
    Then I noticed that my ear was getting warm, and there was a feint bad smell.  Long story short - bye bye KSC75!  Remeasured the output and it was 9v, and the new opamp is very warm.  Giving up for tonight but if anyone knows what it could be please leave your thoughts here.
     
     
     
     
    I'm having a tidy up and came across my first DIY'd amp - a CK2III.  It was working fine in one box but a couple of years ago I put the transformer in a separate box to reduce interference and it never worked again - the op-amp gets untouchably hot in a matter of seconds.  I put it away to fix "later"...
     
    It's now later (and fixing an amp is more fun than tidying!) so I checked the official initial setup section and the first check is the resistance between +/-15v and ground.  To my surprise one is around double the other, but which is correct? [​IMG]

    I then went on to check the voltages at the test points and they were feeble (2.5 and -1.7v) so I checked the transformer outputs while upluged from the amp and can't even get a steady reading so seems that is a good place to start.
     
    I'm going to attempt to find out if I managed to swap the + and - when I moved the transformer but any thoughts on what might be going on would be much appreciated.
     
    At least the LED still works!
     
    EDIT:  Power was correct.  Took out the op-amp and now I get 14.9 and 15.1v, replace the opamp and the power drops again.  I also now have shiny fingertips from touching a very hot opamp!
     
    Edit 2:  What's the easiest mistake a newbie can make?  Putting a part in backwards.  In my case the opamp socket [​IMG]
     
    I'll leave the above intact incase anyone finds themself in the same position but I suspect a replacement will fix my issue.
     
  2. nikongod
    One of your transistors is blowed up. 
    Which one? I dont know. 
     
  3. suicidal_orange

    Last time that happened (in another project) one literally blew up and a chunk flew across the room.  Haven't noticed any damage like that but I guess they can fail without physical signs?  I'll have a closer look, thanks [​IMG] 
     
  4. FallenAngel Contributor
    Completely possible that transistors fail without physical damage, which unfortunately makes debugging lots of fun.
     

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