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Infinity Entra Sub Two repair

Discussion in 'Repairing Electronics' started by Tkeslinky, May 23, 2016.

  1. Tkeslinky

    Tkeslinky New Member

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    Recently, I was given this Infinity sub because it didn't work. The original owner had always planned to repair it, but never got around to it and with spring cleaning it had to go.

    I brought it home and plugged it into my old Sony's LFE out to see what's going on. The sub powered on and went into standby as indicated by the red light on the amp. However, I noticed the light would flicker to green and back to red with the sound of a relay activating and releasing as the occasional lower frequencies of a tv broadcast were going to the sub. I tuned the dish box to an action movie and turned up the sound. The sub turned full on and started producing some sound with authority never going into standby. When I turned the volume down it started going back to standby and you could hear the relay clicking on and off, however, the volume was loud enough that the sub shouldn't be deactivating. I had to give this thing some decent volume to stay active.

    When I tore it down this is what I discovered. This cap, C72 has swollen and burst. (Fig 1) The bottom view showed another problem. A surface mount cap, I believe C71, has also give up the ghost. (Fig 2) There is also a full bottom view of the board (Fig 3) and full top view (Fig 4).

    1) blown C72 top.jpg 2) bottom angle 2.jpg 3) board bottom.jpg 4) board top.jpg

    Replacing the electrolytic on top is not an issue. Should be an easy endeavor. The surface mount has me concerned. I have no way to identify it, but it does appear to be about the same as C74 at the top of figure 2. Any help you guys could provide would be extremely useful. Thanks in advance.

    P.S.
    I did find a service manual for the sub on manualslib.com http://www.manualslib.com/manual/910415/Infinity-Entra-Sub-Two.html However, it doesn't appear to include all of the information about C71 and C74. They are excluded in the parts list on page 22 (23 on website). Looking at the diagram on page 25 (26 on website) I can see they are 0.1uF, but nothing else.
     
    Last edited: May 23, 2016
  2. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Change the electrolytic, that will most probably cure the unit.

    However, the SM problem should be cleaned off the board, there's probably no need to replace it?, although you can if you wish. You don't need to fit an SM one of course, just hang a normal cap across it.
     
  3. Tkeslinky

    Tkeslinky New Member

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    Thanks for the answer. I'll pull both components off the board tonight and clean things up, then I'll run by the local shack tomorrow and see what I can come up with.
     
  4. dave

    Dave New Member

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  5. Tkeslinky

    Tkeslinky New Member

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    Well, ended up ordering the components online. Could not find a radial 6.8uf 100v npe anywhere for a reasonable price so I decided to use an axial that I found on amazon. I did go ahead and replace the smd as well. However, the repairs haven't made any difference in the performance of the sub. It still requires an extremely strong signal (read high volume) before it activates and constantly tries to go back into standby mode as soon as the sound level drops off. There doesn't appear to be any other visually damaged components, but something else is obviously faulty as well. Anyone want to chip in some ideas on where I should start?
     
  6. crutschow

    crutschow Well-Known Member Most Helpful Member

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    The auto-off (mute) circuit appears to be U4-A, U4-B, and associated components on page 26 (web 27) in the manual.
    I would suspect a bad electrolytic such as C35 or C37, and possibly C39, or C1.

    Edit: If push comes to shove and you can't find the problem you can always tie the mute signal low so the amp is always on, and just turn off the power when you are not using it.
     
    Last edited: Jun 2, 2016
  7. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    • Can you measure with a voltmeter?
    • Check Vdc and Vac on V+ and V- then +/-15V
    • The Mute is active low near 0V. unmute logic high which is enabled by the presence of audio or Vac going into the 4 diode bridge. If a diode or large filter Cap on V- is bad it causes an imbalanced DC and/or excessive AC or high V+ with high ripple which over-rides the AC present detect and MUTES the relay.
    • Loading the power supply can reduce the unregulated .V+ or V- and then it unmutes whereas the AC detect should pull down a diode to force a Q On to unmute it if the power supply is working.
     
    Last edited: Jul 1, 2016
  8. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    The 6.8uF must be plastic is my guess looking at schematic, not text.. for low ESR as this is a class D switching Amp and that is a high ripple current filter cap with high SRF. But they dont usually go bad.

    You will find all the parts you need ship same day from Digikey.com
     
  9. spec

    spec Well-Known Member Most Helpful Member

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    Hy Tony,

    I am just asking here: when you say plastic (which you have said elsewhere on ETO) do you mean plastic film capacitor: polyester, polypropylene, etc or are you referring to some other special type?

    Could be that the OP would not know what low ESR or high SRF means. Could you perhaps recommend a specific type of capacitor.

    spec
     
  10. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    • if the documents were not so poor, I could have
    If the links were more readable, I could have been more specific. Generally all,plastic caps are good enough here. The SM caps are possibly ceramic.


    Here read the manual and follow the flow chart page. It is similar to what I said but in more details.

    http://data.manualslib.com/pdf4/92/..._sub_two.pdf?c9b8ff2fc56d808516f57096f85c2906
     
    • Thanks Thanks x 1
  11. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    One cannot search by inhouse p/n but Digikey will have good parts with some search skills
    033-680464-270 NPE Capacitor 6u8/100V K10 (R)1020 GNE 1 C72
    NPE means PolyEthylene.. search by... 6.8uF plastic film then sort by stock, cheapest first. TH or SM is ok on superficial inspection, but details are in the ESR specs in datasheets.
     
  12. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    correction


    NPEmeansnonpolarizede-cap,butifyougetapoorqualitycap,myoumayaswellforgetitandexpectittoburnup.Getapolypropyleneorpolyurethanecapat
    east.itmaycostacouplebucks.
     
  13. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    Ican'tseewhatItypeanymoreonSafarioniPAD
     
  14. delroypstewart

    delroypstewart New Member

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    I had the same problem
    I found out that it was the input of the plug port on the back of the sub that was the problem
    the two wires inside the port of the sub were not touching the jacks head
    so what i did was find a female RCA cord strip it without damaging the soft metal portion on the inside take out the soft metal part that the male jack would touch
    then put it inside the input portion of your left and right input (MAKE SURE IT FITS SNUGLY INTO THE PORT)
    then take a RCA male jack and push it into the port to make sure everything is fitted properly
    This was the only thing that worked for me
    (infinity did not make the ports like what other companies, there port did not have a copper plate for the jack to touch it only has a single wire, this is what causes the playing problems)

    GOOD LUCK
     
  15. delroypstewart

    delroypstewart New Member

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    check the c12 and 78 capacitors they might be loose also make sure where the sub speaker cord connects to the mother board is secure it might not be connected properly so sodder the board area again that is what i did now my sub works.
     
    Last edited: Jun 30, 2017

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