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Identifying a molten blob

Discussion in 'Electronic Repair' started by N Cook, Jul 12, 2007.

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  1. N Cook

    N Cook Guest

    From a 2003 Carlsbro 8400 , 400W mixer amp that immolated itself.
    Anyone have a schematic or parts listing.
    Assuming that Q319 is a high voltage TO92 2N5551 ( totally burnt and erupted
    but 2 isolated lighter blobs on the remnant of TO92 face are in the position
    of the isolated printed 2N of other 2N5551s on the board) then the melted
    blob component goes from the base of this feedback transistor to the speaker
    output line via the relay. So probably something like 47K 1/3W resistor. The
    board is also burnt so overlay for this blob also missing. Anyone ever come
    across a metal oxide resistor melted to a 3mm diameter blob like a small
    tantalum. Metallic grey blob that measures 40 to 150 ohm or so across
    diameters.
    The thermal heatsink monitor tranny was also exploded but as the face was
    gooed to the heatsink, that face was spared from charring/shattering and
    that was 2N5551 also.

    You'd think Carlsbro would know better.
    The subframe inside the chipboard casing is held to the chipboard with 12 x
    4mm bolts, yes machine screws screwed into chipboard, not even ordinary
    woodscrews, let alone proper twin-start long pitch chipboard screws.
    2 had dropped out and because you carry this kit vertically but use
    horizontally, plenty of chances for 1 inch long steel screws to roll into
    the power amp. Audience were treated to piles of smoke erupting from the
    back of the amp - Hendrix was more impressive.

    Plenty of other damage but identifiable components for the others.
    Do you get a sensible response from technical email enquiries to Carlsbro
    and do I mention about their crass construction methods. ?
     
  2. Ron(UK)

    Ron(UK) Guest

    I think you'll find that these amps are made in China by Phonic. You`ll
    come across the same series of amplifiers carrying various brand names
    including Yamaha.
    That`s why they are so inexpensive.
    Carlsbro have an excellent technical department, and will answer tech
    enquiries by email.
    I`m sure that they already know, but as it`s just a rebranded product,
    and not actually manufactured by them in house, there`s probably not a
    lot that they can do about it.

    Not all Carlsbro stuff is crap btw, the Gamma series of moulded speaker
    cabinets are quite excellent - for the price. Sadly in common with most
    'British manufacturers' these days, I can buy them retail a lot cheaper
    than the trade price, so I dont sell them anymore.

    Ron(UK)
     
  3. Arfa Daily

    Arfa Daily Guest

    I have in the past, but I'm not sure it would be - how shall we say -
    helpful ? - to mention "construction" and "crass" in the same sentence to
    them ... d;~}

    Arfa
     
  4. N Cook

    N Cook Guest

    Construction not quite that bad on further exploring. They must have put 4mm
    clinch nuts on the outer surface of the chipboard covered by the vinyl
    cloth. But only plain washers and not star or spring washers under the heads
    and no varnish /glue spots over the heads to stop any undoing.
     
  5. N Cook

    N Cook Guest

    At least , so far, the cgi system has placed my request on their "in tray"
    section of their www site, with only me and them capable of viewing - I'm
    quite impressed with that. Better than an auto email reply.
    I made no mention of non-captive screws, its not even used on top of a
    speaker cab so only vibration would be through the floor
     
  6. Ron(UK)

    Ron(UK) Guest


    I`ve seen several where the internal parts have been flopping about
    inside the box. The better quality versions have a moulded cabinet and a
    SMPS. They sound a lot better also.

    Ron(UK)
     
  7. N Cook

    N Cook Guest

    Oriental script on the mains transformer and on a schematic.
    Q319 was 2N5401 and the R was 330 ohm. I'd not thought about it but VxV/R
    heating with single rail of amp voltages to melt a 1/3W resistor, not charr
    or explode it, it must be about 300 ohms or 10 watts dissipation.
    Carlsbro, presumably for anti-distribution reasons, email truncated jpegs of
    schematics. They display the perhaps about 80 percent of the original on
    Firefox or IE but you can't save as jpeg. You go through the motions of
    saving as jpeg , no error message appears, but nothing saved in the relevant
    directory. Other than saving to file as a rather useless .prn, printing off
    the screen and scanning in , or photoing off the screen and montaging,
    anyone know of a work-around to this.
    Someone recently on s.e.r started a thread on how to deliberately send
    uncopiable files to others - this runs close.
     
  8. N Cook

    N Cook Guest

    One of those mysteries of the internet.
    They emailed the schema to a browser based account of mine that does not
    have filters on it. Downloading to firefox or IE produced truncated but
    viewable images that could not be saved to disc.

    Forwarding those attachements from browser account to my main email account
    with filters temporarily lifted to download, then saving those attachements
    to disc as jpg, then all 5 were readable ,complete un-truncated pages. I've
    never had to do that before.
     
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