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Extending the life of a Tek 2465?

Discussion in 'Electronic Repair' started by DaveC, Nov 21, 2003.

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  1. DaveC

    DaveC Guest

    Surplus electronics shop here in Sillycon Valley.
    Intuitively, it just seemed like the right decision.
    There are little vinyl "nipples" that slip over the studs to insulate them.
    Just be sure to put them back on when you've finished the job. Might be
    prudent to trim those nipples to accomodate the additional height of the nuts
    and heat sink. Not much, just a few mm.

    There is a flat cable connector that plugs onto header J102; you can see the
    header pins in this photo:

    http://home.covad.net/~peninsula/Before.jpg

    It's easy to pull the connector off. I didn't notice, and got Counter/Timer
    option errors on startup. (If you don't have C/T option, might not have this
    connector; don't know...). Also was told that it is common to pull off one of
    the coax cables running through this area, which gives similar power-on
    diagnostics errors.

    This heat sink fits nicely over the J102 connector when properly installed.
    Was like it was made for this application :)

    Don't overtighten the nuts. You could stress the studs and possibly pull them
    from the PCB, which means they might come out and bounce around the circuit
    area (!). Not a good thing... :)

    Good luck,
     
  2. DaveC

    DaveC Guest

    On further consideration, I haven't done all that much to properly heat sink
    this IC.

    Most of the heat is coming from the metal "substrate", the built-in heat-sink
    which is visible as a tab under the nut on the right end, and a notch under
    the nut on the left end:

    http://home.covad.net/~peninsula/Before.jpg

    My heat sink contacts the full surface of the IC's plastic body, which is
    radiating a minimal amount of heat. There is a #4-40 nut between the tab and
    the black heat sink on the right end only. This is all that is conducting
    heat from the tab to the sink. On the left end, there is no contact at all
    between the metal substrate and the black heat sink, except whatever might be
    coincidentally conducted through the stud (which probaly 'aint much):

    http://home.covad.net/~peninsula/After.jpg

    To do this project right would require some kind of machined spacer for both
    ends, one to fit the tab's square area, and the other the notch's. Both would
    have to be no greater than the distance from the body's surface to the metal
    substrate's surface. Pretty small requirements for machining such parts.

    Might cobble something together to do this. Have to see how resources become
    available...

    In the mean time, I'll keep the scope in Normal sweep mode when it's powered
    on, which keeps the display blank. This, as pointed out by someone in this
    ng, keeps U400 working less, and hence, cooler, when it's not needed.

    Enjoy,
     
  3. Jim Yanik

    Jim Yanik Guest

    If the option(s) are not installed,or does not require a signal
    pickoff,there are jumpers that are installed;see your schematic for the
    vertical section.
     
  4. Cut a strip of thin sheet metal (beer can is good) whose width is the
    same as the height of spacer you require, and roll it round the shaft of
    a suitable screwdriver. Cut off the surplus. Instant spacer with no
    lathe in sight. For a thicker wall, roll more than one turn.
     
  5. DaveC

    DaveC Guest

    Thanks, John. Simple solution. But that's a mighty thin spacer... the
    distance from the top of the IC to the top of the tab:

    http://home.covad.net/~peninsula/Before.jpg

    Maybe just several layers of mashed beer can, w/o the wrapping exercise?
     
  6. I can't tell what thickness you need from the picture. But I assumed
    from what you wrote that it was thicker than a normal washer.
     
  7. JW

    JW Guest

    How about a bunch of washers with thermal paste between each one?
     
  8. DaveC

    DaveC Guest

    Yes, maybe 3/32 inch (1.2 mm). I put a thin #4-40 nut on top of the tab to
    hold it to the PCB, then the new sink, then the original nut and
    star-lock-combo you see. I'd rather replace the thin nut (its surfaces are
    quite curved; not near the total surface area of the tab) with something
    larger and more thermally conductive.

    Is it really more helpful, thermally, to take off the anodize from the under
    side of the heat sink (as long as it is smooth)? Can steel wool accomplish
    this?

    Thanks,
     
  9. DaveC

    DaveC Guest

    Great idea. But because of the small area, I'll have to use it in a "z"
    shaped form, folded several times, rather than rolled.

    Anyone know of a non-food product that comes in aluminum cans? I'd like to
    use thin aluminum sheet, but without the need to remove that inner coating
    that protects food and drinks from the aluminum.

    I could sand off this layer from beer can or such, but then I'm looking at
    roughening up the surface, which would 1) reduce the thermal transfer
    properties, and 2) make the aluminum thinner.

    Ideas?

    Thanks,
     
  10. DaveC

    DaveC Guest

    It is a Thermalloy product:

    < http://www.thermalloy.com/bin/stdisp.pl?Pnum=507222b00000>

    Although I've now decided it's not long enough. I want one to extend the
    entire length of the IC, including the maximum measurement of the metal
    substrate.
     
  11. No. The anodizing is very thin and doesn't have a particularly poor
    thermal conductivity anyway.

    If steel wool will get it off, it's paint, not anodizing. Anodizing is a
    layer of dyed aluminium oxide, chemically bonded to the aluminium mass.
     
  12. Now I don't understand what you are trying to do. I thought you just
    wanted a spacer. Beer can material isn't good thermally; the aluminium
    is in a 'hard' metallurgical state, which reduces its thermal
    conductivity. The same applied to kitchen foil.
    If the thermal conductivity matters, scrounge a tiny bit of soft or
    quarter-hard thin sheet from your local metal converter. Or you could
    make a ring out of copper wire a bit thicker than you need finally and
    file off top and bottom surfaces to give you a better thermal contact.
    Forget it.

    Incidentally, I make heat sinks for my own stuff and
    repairs/improvements out of bits of scrap copper water pipe.
     
  13. DaveC

    DaveC Guest

    Yes, I want to get the heat from the tab to the bottom of the heat sink, a
    distance of about 1.2 mm. Thermal properties count.
    Copper sounds ideal. I'm sure I could find a piece of copper that thickness.

    Thanks,
     
  14. Jim Yanik

    Jim Yanik Guest

    Looking at the pix on your site,it seems to me you have adequate contact
    already.Maybe if you can find a surplus HS a tad longer,sure,go ahead,but I
    doubt you'll gain much in dissipation over what you have now.
    IMO,a different style HS with fins closed to the center of the IC substrate
    would be best,as the HS cross-section(thickness) limits what heat gets
    dissipated.
    But hey,it's your scope.
     
  15. mike

    mike Guest

    All this is very entertaining. But you're shooting in the dark.
    It's like watching a bunch of drunk guys sitting in a bar talking about
    women.
    Nobody has a clue, but they all have a technique. ;-)

    Why not measure the temperature of the &*&&^%G tab and DESIGN a solution?
    You remember...temperature delta, thermal conductivity, path length, air
    flow...? Understand the problem before designing the solution!!!

    mike

    --
    Bunch of stuff For Sale and Wanted at the link below.
    Toshiba & Compaq LiIon Batteries, Test Equipment
    Honda CB-125S
    TEK Sampling Sweep Plugin and RM564
    Tek 2465 $800, ham radio, 30pS pulser
    Tektronix Concept Books, spot welding head...
    http://www.geocities.com/SiliconValley/Monitor/4710/
     
  16. DaveC

    DaveC Guest

    The contact between the tab and my heat sink is provided by a #4-40 nut. The
    nut is come kind of steel, not real flat on either side. It is about maybe 50
    percent of the area of the tab. That's not real good conductivity between the
    two. I'd like to make something of aluminum that is closer to the size of the
    tab. And I'd like to also provide a similar heat "pipe" for notch at the
    other end.
     
  17. DaveC

    DaveC Guest

    And my heat sink doesn't even cover the nut completely. Looking at the photo,
    the heat sink ends before it extends completely under the nut:

    http://home.covad.net/~peninsula/After.jpg

    The heat sink covers the majority of the IC, but that's mostly plastic, and
    the heat is radiated mostly by the two exposed metal parts.

    it needs reworking...
     
  18. Jim Yanik

    Jim Yanik Guest

    ISTR that the metal substrate is exposed on the top side of the IC for most
    of the length of the IC.
    You should be getting pretty decent thermal contact.
     
  19. mike

    mike Guest

    Jim, I'm really confused by this.
    Are we looking at the same picture?
    http://home.covad.net/~peninsula/Before.jpg
    If the terms "metal substrate" and "tab" are different terms for
    the same heat sink structure of the IC, your statement conflicts with
    the picture.
    What am I missing?
    mike

    --
    Bunch of stuff For Sale and Wanted at the link below.
    Toshiba & Compaq LiIon Batteries, Test Equipment
    Honda CB-125S
    TEK Sampling Sweep Plugin and RM564
    Tek 2465 $800, ham radio, 30pS pulser
    Tektronix Concept Books, spot welding head...
    http://www.geocities.com/SiliconValley/Monitor/4710/
     
  20. Jim Yanik

    Jim Yanik Guest

    OK,I was thinking(perhaps it's the earlier version I recall) that the metal
    substrate was exposed for the whole length of the IC,not just the tab.
    My fault.
    So,what I would do is cut a small square piece of sheet copper(or
    aluminum),drill a hole for the stud,place it between the tab and the HS,and
    a smaller one for the narrow slot,use thermal grease,too_Or trim a copper
    washer to size.
    Perhaps an old penny? not the new zinc ones.

    Heck,maybe THATS why the IC is prone to failure;they changed the packaging
    and thermal dissipation with a full plastic DIP package,instead of the
    bared substrate IC as ISTR.
    (Of course,being an old geezer,my memory sometimes fails me) :cool:
     
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