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which way should cooling fan blow?

Discussion in 'Hobby Electronics' started by Peter Howard, Dec 19, 2004.

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  1. Peter Howard

    Peter Howard Guest

    In the last half of 2003 I bought a Digitrex GKX9000 DVD recorder from Big
    W. Big mistake, as I found out when I started frequenting an Australian
    website and forum devoted entirely to the GKX9000 (The site seems to be no
    longer in existence). It was full of reports of the failings of this unit
    and the non-responsiveness of the local distributors and warranty service
    people. By the time I decided it was a dead loss I'd mislaid the receipt and
    packaging and so could not return it to Big W.
    I've just bought a decent standalone DVDR, but in a spirit of general
    cussedness or masochism I'm taking another look at the Digitrex. One of the
    many failings of this model was frequent lockups when it would not respond
    to any button pushes or remote control commands. Others besides me observed
    that it would often lock up part way through a recording, or fail to start
    recording at a preset time. Only way to reawaken it was to unplug it from
    the mains and power up again.

    I know next to nothing about DVDR's but on opening the Digitrex up I see a
    disk drive, an SMPS board, an I/O board and what seems to be a processor
    board sporting a many-pinned SM chip with an aluminium heatsink stuck to it.
    There is no cooling fan on heatsink and the only existing fan is a 40 mm
    exhaust job at the other end of the case. As I know from experience, a PC
    with a failed CPU fan goes into thermal shutdown. Could it be that this CPU
    (if that's what it is) in the Digitrex needs more cooling than it gets?
    The top cover of the unit is 38mm above the top of the heatsink, ample room
    to carve a round hole in the top cover and fit an 80 mm 12v fan I happen to
    have. I'm game to experiment along these lines because I'd hesitate to even
    give this POS away let alone Ebay it to another unsuspecting boob.

    The question is, should I arrange this fan to blow room temperature air onto
    the CPU heatsink or suck warm air out of the case?
    And should I incorporate a spacer to get the fan which is 20mm thick as
    close as possible to the heatsink?
    The 40 mm fan at the far end of the case sucks air and there's room to fit
    one or more extras beside it if I wanted to be sure of creating a little
    more negative pressure inside the case.

  2. Lord Garth

    Lord Garth Guest

    When my Oritron DVD player quit responding to remote or front panel
    commands, I opened
    it and discovered two blown electrolytic capacitors on the SMPS board.
    Replacing these
    cured the machine. The front panel indicated power at all times during the
  3. KLR

    KLR Guest

    If you are putting the fan in the top of the case - then have it
    blowing UP. Since hot air rises naturally - this natural action will
    work with the fan helping blow in same direction instead of against

    Spacing it so it gets to the heatsink will certainly help - if the
    heatsink is getting very hot in normal use.

    If the thing gets really hot - and the IC underneath is similar shape
    to a computer processor - it might be worthwhile actually installing a
    CPU heatsink and inbuilt fan assembly :)

    if its been running hot or overheated in the past, then you could
    check for dry or bad solder joints under heatsinked devices, and also
    check for eletrolytics too as they tend to have a reduced life when

    Don't go overboard with fans though, in my experience they should only
    be used as a last resort as they tend to suck heaps of dirt and dust
    and crap into the unit, which in extreme cases:

    1>blankets components, helping keep them hot,
    2>gets into mechanical parts causing failures
    3>clogs fins of heatsinks. vents and so on

    if they fail, (and they do often) damage can occur to heat sensitive

    in my opinion, good natural ventilaion, generous heatsinking areas and
    should be a priority where it is practical or possible to do so.
    Unfortunately with modern high performance processors and other chips,
    short of slowing them down and bigger heatsinks (which defeats the
    purpose of having them) - there isn't a lot you can do to avoid fans
    in the real world.
  4. budgie

    budgie Guest

    But if the O/P's machine responded after power cycling, it's a fair bet his
    problem is different.
  5. Lord Garth

    Lord Garth Guest

  6. WDino

    WDino Guest

    Many of the cheaper DVD recorders had two main problems, cooling and power
    supplies, but even Panasonics and Pioneers also come in with similar faults
    Both the CPU and the actual DVD writer tended to get too hot. The better
    machines and later cheaper ones have CPUs with larger heatsinks. The DVD writer
    is just a standard PC unit and can be replaced with a better one if desired.
    Small fans blowing onto each have been known to help but I prefer to put a
    larger fan inside the case blowing OUT.

    As for the power supplies, the final filter capacitors tend to fail, usually
    because they were mounted too close to the heat producing parts of the power
    supply. Another fault was that the 5v supply drifted too LOW in voltage. In many
    cases, DVD recorders came to me for repair that worked perfectly on my bench.
    But when the 5v supply was checked it was less than 4.6V. Tweaking it up to 5.0V
    usually fixed the machine for the customer.
    The Digitrex GKX9000 DVD recorder is one that can need adjusting.
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