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Warwick Tubepath 5.1 amp

Discussion in 'Electronic Repair' started by N_Cook, Feb 5, 2013.

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  1. N_Cook

    N_Cook Guest

    Believed to have been making an "electrical smoke" smell but performed
    faultlessly for a gig, just general smokey smell , nothing specific to this
    amp, I am trying again to find out why this amp is supposed suspect and not
    anything else.
    During the gig the stage supply tripped out. Nothing found amiss and powered
    up lights and amps and continued .

    No discolourations / open Rs/ open user or 7 internal fuses etc. Removed the
    Zobell R and it is .8R rather than 1.5 ohm , but I don't think is
    discoloured enough to have been burning.
    No disc ceramics etc between ground and live / neutral.
    Filter block X2 type 375V ac across L-N marked .1uF R .46 measured .024uF on
    C and 1.2K on R scale on 1KHz RLC meter. Now hacked into and no sign of
    smoke or overheating inside the cladding. It lays next to the dropper for
    the mains relay and slightly discoloured cladding ,one-sided externally,
    from that proximity probably.
    Currently exploring the power amp which looks fine but in case one or more
    transistors has gone open circuit and brief enough short circuit to trip the
    mains trip but not any fuses .
    No trace of smoke around the large mains Tx but will unbolt to check
    underneath.
    Any other suspects that would leve no trace?
    How to find a problem , if there is not one to find?
     
  2. N_Cook

    N_Cook Guest

    Tried a new X2 on the same meter, marked .1uF + 100R
    this measures .1uF on C and 140R on R range, perhaps a bit more hacking
    into the original , maybe there is a trace of brown around the pins
     
  3. N_Cook

    N_Cook Guest

    I don't think there was a resistor in the original mains filter .
    Hacked in , breaking the sort of sintered looking
    metal at the leads leaving the metal to the capacitor at each end and 0 ohm
    lumps that hold the leads.
    I sacrificed a .1uF-100R new one and a very definite 3 band 100 ohm .5W
    ceramic/MO resistor in that between one terminal lead and the sintery edge
    of the capacitor.
     
  4. Baron

    Baron Guest

    N_Cook Inscribed thus:
    Exploding tantalum bead cap !
     
  5. N_Cook

    N_Cook Guest

    Unwrapped the X2 cap , 1.7m long with a meandering 80 percent continuous
    spark errosion line along the length averaging to the middle but no obvious
    burnt or melted patches. Whether thousands of instantaneous discharges would
    trip out an MCB or imbalance RCCD/ELCB/ GFCI , no idea.

    Owner had removed the cover and extracted a load of fluff from inside the
    minor fan air path. 4 of the 6 close pasked emitter Rs had faded printing
    plus the changed value Zobell , perhaps them seriously overheating was
    causing the electrical smoke smell. Change the X2 and Zobell and externally
    cleanable filter cloth going over the minor fan.
    the main fan you can shine a torch through front to back to check for any
    blockage

    The mains Tx nut was loose but no smoke trails inside other than black
    soft-plastic plasticiser, from the disc pads, leeching and brown staining of
    2 bits of sticky tape that hold the white high temp covering tape winding in
    place.
     
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