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Blue Paste?

Discussion in 'General Electronics Discussion' started by oakdust, Oct 22, 2010.

  1. oakdust

    oakdust

    38
    0
    Feb 27, 2010
    I found a blown termal fuse on the top of a resistor. The fuse was covered with a blue dreid paste. Can anyone tell me what to use over the top of the fuse when I replace the resistor and the fuse?
    Thanks
     
  2. shrtrnd

    shrtrnd

    3,651
    449
    Jan 15, 2010
    My guess would be, the blue paste was just something used by the manufacturer to hold the assembly of resistor and thermal fuse together, when they assembled the circuit. (Easier for assembler to install a ready-made single piece, than sit there and solder the two pieces together during the assembly process).
    I can think of no electronically sound reason (heat dissipation, or anything like that), for the blue paste to be there.
    I seriously doubt you need to replace the blue paste, to complete your repair.
     
  3. shrtrnd

    shrtrnd

    3,651
    449
    Jan 15, 2010
    Nuts,...
    I probably gave you a bum scoop on your blue paste.
    I was talking to a guy at work, who believes your blue paste was probably to facilitate THERMAL TRANSFER of heat from the resistor to the thermal fuse. (To better transfer the heat from the resistor to the thermal fuse).
    If somebody doesn't come up with a supplier of the blue paste on this site for you, what I would do, is pack the area between the resistor and the thermal fuse with thermal grease (the white paste you use between power transistors and heat sinks when you mount them, made out of silicon), and then put epoxy over the pair, so you don't make a big mess with the thermal grease (that stays moist for a long time).
    We both learned something from this.
    Good luck
     
  4. oakdust

    oakdust

    38
    0
    Feb 27, 2010
    Thanks, I was thinking maybe an RTV sealer like they use in the auto industry but not sure if it is a conductor or not.
     
  5. shrtrnd

    shrtrnd

    3,651
    449
    Jan 15, 2010
    I don't know how good an electrical conductor RTV would be. But it would just hold the two parts in place, and wouldn't help to transfer the heat from the resistor to the thermal fuse very well either. I don't know how sensitive the whole shebang needs to be. I would think just making sure the thermal fuse is in contact with the resistor would be good enough,... but actually using a compound to help transfer the heat to the thermal fuse would probably be best.
    Hope somebody gets on this site, with the equivalent of the blue paste you need, ...
     
  6. oakdust

    oakdust

    38
    0
    Feb 27, 2010
    I'll check radio shack " you got questions we have answers' I just like tt see the deer in the headlights look when I ask a question. LOL
     
  7. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    Hehe, I can relate to that last expectation..! :D

    Imho a heat conductive glue would only contribute slightly to the speed of which the thermal fuse would blow, long term it would not matter much if you used ordinary rtv.
    Heat conductive glues exists but are very expensive. Just stay away from the acid-smelling rtv's - which are corrosive.
    If you want to go fancy you could try get hold of some aluminum oxide and mix in a dab of ordinary rtv. Heat conductive paste incorporates AlO, or silver in extreme types.
     
  8. oakdust

    oakdust

    38
    0
    Feb 27, 2010
    Cool! mix stuff together!
    Maybe I'll just try it without any paste. Any opinions on not using the paste?
     
  9. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    Yeah, the paste contains some kind of grease which I figure will be bad for the rtv properties, you'll want to use dry aluminum oxide powder mixed in the rtv.
    Or failing that, just use a dab of paste, covering it with something, as shrtrnd suggested in his second post.
    Or just use plain rtv altogether. Until proven otherwise I don't believe this is rocket science.
     
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