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Repair a KRK 10s Subwoofer - parts id

Discussion in 'Repairing Electronics' started by chinjazz, Nov 9, 2016.

  1. GromTag

    GromTag Active Member

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    I am still looking at those thermalloy, for their really being non conductive. Overall the data shows it to be thermally conductive not electrically conductive. also that thermal grease should be used to help along further, even with the small drop in heat transfer with the grease.

    And yes the shipping cost are all ways an issue. To be made aware, that if needed this project can be assembled given time if required, as there is no rush on getting anything, this forum posting can be used as a go back to reference on getting things.
    Time taken to get an idea on a plan and then implement it, I'll admit I've been stating things about what could work, perhaps I should have mentioned much sooner that the concept was gathering a list. Then implementation that you find reasonable.

    You just really want to get this amp fixed don't you.:)

    thus far, the resistors show compatibility. http://www.mouser.com/ProductDetail/TE-Connectivity-Neohm/LR1F1K0
    and http://www.mouser.com/ProductDetail/TE-Connectivity-Neohm/LR1F68R
    .

    Transistor http://www.digikey.com/product-deta...-components/2SC14730RA/2SC14730RACT-ND/972412
    only because Digi has them even tho they are now obsolete, they have (even with a non updated stock percent) 4,183 left.
     
  2. GromTag

    GromTag Active Member

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    The Shipping for Mouser is a bit slow at times, they should be able to comply with this, or try to. If any tracking info is avail (Private info for your own use, please no posting here, can lead to personal address.) Then that would be an indicator that when the resistors have shipped, and yes a few extras, not only for spares, but fir just in case all round is a good plan.

    meaning if it is possible to intercept based on, if it has shipped, it shipped.
     
  3. GromTag

    GromTag Active Member

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  4. dave

    Dave New Member

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  5. chinjazz

    chinjazz Member

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    I thought this second go round was like a ray of hope beaming thru, where originally thought to only identify a few parts.
    And yes this was truly accomplished with your help. Accomplished to find compatible parts to the design that should work.
    I'm in no rush to get it done, but yes I'm motivated.
     
  6. chinjazz

    chinjazz Member

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    Since I ordered it on Sunday, If I called them first thing when they opened on Monday I may have a slim chance
    to add on to that order before it was packed up.. But I kind of doubt they would be packing 4 resistors at the "opening bell" (LOL).
     
  7. chinjazz

    chinjazz Member

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    Also seems to be ergonomic with ease of use in mind compared to the other one.
     
  8. GromTag

    GromTag Active Member

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    :Not relevant to topic directly:
    I do miss the days when I could go into a shop and the shelves have things that I could never even emagine a use for. Now lucky to even find applicable wire. A hunt and find starts, different stores, even towns visited, what would work in place of, what could be used for, even if on the internet referring to info based on what it says vs what it might mean, (however datasheets are usually the best bet, however some have been wrong from time to time, all be that's rare depending on circumstance) wordplay on many things here (edit. At my hometown) have been overly exaggerated to the point that I wouldn't doubt that even the designers and the manufacturer both looking at what ever couldn't tell what it is or does. And their the ones that made it. Well they say so, but the label on the back says mad by such and such for such and such. One conveniently starts trying to hide that label.:( as if I didn't see that.
     
    Last edited: Nov 27, 2016
  9. GromTag

    GromTag Active Member

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    And yes that grease does show applicable use for that amp.
    Arctic MX-4 paste, this is not a grease, however still applicable, just a bit more tough. to apply and to spread, should make it better for staying in place. as computer processors can get quite hot just as those transistors when the amp is floored on volume for a period of time, FYI, the sub cone travel producing some airflow is the cooling fan for them so to speak.
     
  10. GromTag

    GromTag Active Member

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    An update on the thermal plates Aavid Thermalloy Polyimide, there is no indicator of modified parts in the material, nor incompatibility with frequency switching devices, all tho I am still not 100% on them for that use.
    In amplification use for switching supplies, at times the frequency of the switching can respond to certain materials used in thermal pads, all be this is quite low to not even be noticeable in regards to amplification uses. It's just that some insulating thermal plates can cause slight issues with actually affecting switching speeds that far exceed you amplifiers capability. Therefor that range has been excluded from my reasoning on the Thermalloy part.

    As for general use as a thermal pad and electrical insulator in this particular amplifier project, I see no problem, just as long as it fits via the size spec for that part from Mouser, with the part having any issues in this application. Main concept it is a bit overkill tbh. Tho with the tensile strength of 25,000 PSI, as indicated by Mouser's listing of specs. And a temperature range of -260 C (-436 deg F) Cold range to 240 C (464 deg F) Hot ranges. And a thickness of 0.05 mm (0.002 inch). And if by any means the color Amber is not an issue to you, then the part fits the part, so to speak. All be it just a tad bit smaller than those original mica plates.

    Also my spelling of Capton, it's actually spelled Kapton, (bad habit on my part) for the material also present in these Thermalloy pads.

    They show to be usable in you application based on specs mentioned from Mouser and the Aavid site.
    These pads in the datasheet are the 43-77-20G, that places them at the For TO-220, TO-126, Case 77, Case 199, Case 90, TO-218, TO-3P.

    The TO-3P are the closest match up to your driving transistors, just a reference to the housing, this data sheet is a reference only, and is very not likely to be a correct match to yours. Just the package housing parameter in the Package Dimensions section.

    http://www.onsemi.com/pub_link/Collateral/ENA0188-D.PDF
     
  11. chinjazz

    chinjazz Member

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    I hear you. I grew up in Manhattan, and had access to literally everything store wise. But even now I'm sure there are less places
    that actually have inventory you could see and touch. In the downtown area called Tribeca when I was a teen I worked in a store
    called Metro Electronics, and it was truly an electronics everything.. Great memories there!
     
  12. chinjazz

    chinjazz Member

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    Thanks!
    The cross referencing process you performed to find this compatibility must have been a heavy task.
    Wow, I do wonder if this could somehow been automated with computers?
    How actually did you go about doing this?
     
  13. chinjazz

    chinjazz Member

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    I called customer service @ Mouser this am and Stephanie in customer services did right by me.
    I was able to order the Aavid, and she waived shipping! Nice people are out there :)
     
  14. GromTag

    GromTag Active Member

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    On the Thermal pads, I was just checking to make sure that the pads would be ok to work with switching transistors, some materials used in the thermal pads can sometimes lead to minor issues with high frequency, or actually have minor electrical transfer to help heat pass. The term thermally conductive and electrically conductive can get easy to cross. I just used the datasheet to see that the materials involved, Kapton, plastic and the more direct term used, a direct term "improved" replacement for mica in the data descriptions.

    Here.http://www.aavid.com/product-group/interface/films-insulating
    And as for the concern about making sure not to get conductive types, this is an example of blend material that conducts Both heat and energy on the electric level and exist in many forms and shapes.

    http://www.digikey.com/us/en/ph/Lai...ml?WT.srch=1&gclid=CK-D1f7Ty9ACFVU7gQodjoQAMA
    As for virtual automation, the systems used by the design and manufacturer of the involved methods are various in counting them would be an actual task, or if the info exist on google somewhere just needing the correct wording in search criteria.

    That's good to hear on the corrected order from Mouser.
     
  15. GromTag

    GromTag Active Member

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    Also, on the thermal past and pads If you choose to, if the pads are large enough, place the grease/past on the transistor then spread even, then place the pad leaving the pad to sink side uncoated for better heat transfer directly to the sink. As the material being used for thr thermal pad has better effect than usual pads that I have here. Quite similar to the way the original mica insulators were used on that amp during disassembly. If any pads turn out to be smaller on projects similar to this or identical to this one, and the pads are not quite to size, non conductive (verified) grease/paste can be used in a pinch to fill in the difference as long as it's not too small an insulator pad for any given transistor, as well as care in that in installing the part without possible metal to metal contact is checked.

    As for checking things after assembly

    After assembly, the multi tool on auto range, and with no power to components being checked, place one test lead to the metal sink, then the other, check readings, should be continuity 0 Ohms confirming sink has any coatings that could interfere with testing.
    Test lead (either) to heat sink, then test each transistor point looking for low value resistance, typically a low value such as 0-100 Ohms is a potential short, (the value should read infinite during testing on any pins to heat sink) thus the transistor is making direct/indirect contact to the sink, as for the correct values for that amp, I do not know them, many amps have different ranges due to the transistors used.

    However the center pin on many transistors BJT and FETS alike, is the main check use for the middle pin to the sink for continuity in Ohms mode, as the buzzer type test can energize the part far more than the Ohms test mode, so avoid using the audible test methods on transistor parts.
     
  16. chinjazz

    chinjazz Member

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    Thanks for the extra detailed instructions. I did wonder about what layers / order of the paste/pad assembly.. I seem to recall that on the original installation there was paste on the transistor and the sink side, but maybe that's because the mica is so thin. It was definitely curious to me because I never disassembled a unit like this with grease. At first I thought it was a negative affect of operations, but then I noticed it everywhere. I think it was also along the bottom of the sink itself where it met the chassis of the box. I wiped much of it up.

    By the way, I ordered everything and it all should begin shipping today.
     
  17. GromTag

    GromTag Active Member

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    Also if the board has charge in the caps, the readings from the multi tool will show very odd results, So since you would not likely have an method to discharge them and hold them low, you can omit the multi tool test for the three lead check.

    This amp is a Class D hyper, with dual power banks, one for the positive rail and the other negative.
    Your amp can have different results on the three pins to heat sink. However should NOT read zero Ohm continuity, they should read infinite. Any questions please ask.
     

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  18. GromTag

    GromTag Active Member

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    Grease on the sink to chassis, that sounds a method to help prevent the housing from becoming live if a short, or only one transistor makes contact to the sink and transfers its energy. Similar to the cap of death for older auto transformed guitar amps. Note that the power from the transistor is high, tho not connected to the main power in from the mains as the death cap is on old guitar amps.
     
  19. GromTag

    GromTag Active Member

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    Also if 3 pins are tested and any start to climb in reading, That;s a charging effect to a cap as the parts are connected to the board and surrounding components. That's an ok result. Again, just no continuity as example if both test leads were crossed.
     
  20. GromTag

    GromTag Active Member

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    Just need to check up on verifying the parts, The blue resistor is bugging me. If it has Blue, Grey, black, Gold, Brown. then it is a 68 Ohm.

    However, if it has Blue, Grey, Black, Brown, Brown, then it is a 6.8 Kilo ohm. The images I've seen show it to be a 68 Ohm. However I can only enhance the image so far. The pull down resistor is usually low, As to following the tracks on the board, the corroded transistor is responsible for operating the switching control transistors for the main drivers. This is being noticed only recent (the resistor).
     

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    Last edited: Nov 29, 2016
  21. GromTag

    GromTag Active Member

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    If it matches R494, then ok.
     

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