JBL Authentics L8 SMPS

Discussion in 'Power Electronics' started by Adrian Mos, Dec 15, 2016.

  1. Adrian Mos

    Thread Starter New Member

    Dec 15, 2016
    4
    1
    I have a JBL authentics L8 found at the dumpster. The unit has to rotary encoders one for volume/power and one for source select. When i first plugged it in, the vol/power didn't lit up, and the source one was blinking and that was all. My immediate thought was that something's wrong with the smps so i've opened it up and start looking. There was no visual indication on the smps of something wrong so i've started checking the caps. Nothing wrong there. In the min while one day i was trying to check the pwm IC and by mistake i've shorted it. The worst of all is the bottom part is filled with smd's and the ones around the IC got roasted, on some of them i can't read anymore the value. I've tried to find the service manual, but the only one you can get is far for complete and doesn't include the schematic for smps.

    So i was thinking before i go nuts, just in case there's some issue with the main board, to try and power it using something else. I got myself a PSU from a PC and 2 buck converters of high power but unfortunately no luck.
    What i get now is the source doesn't lit up, but the power does. When i press the power button the lights goes on with a circling motion and every time it makes a full rotation it blinks and after ~4 turns it turns off.
    I have to connectors for power on it, one that it seems to be for the amps of 19V 4A and one for the logics that runs at 7.5V. Ive tried to supply both. But there's an AC pin that i have no clue what it does. If i take out the power on the 19V rail the unit still powers on like i said above.
    smps.jpg 20161215_211126.jpg 2016-08-24 18.49.03.jpg
     
    Last edited by a moderator: Dec 23, 2017
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  2. fpaiva

    New Member

    Dec 2, 2017
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    Hi Adrian, did you fix your problem? Mine just started today!
     
  3. Adrian Mos

    Thread Starter New Member

    Dec 15, 2016
    4
    1
    I still can't find the schematic for the power supply so I'm stuck with those smd parts that i can't read. Do you have JBL authentics L8?
     
  4. drops206

    New Member

    Dec 20, 2017
    9
    2
    What do You need? I have L8 and L16 with the same issue.

    DD4FDFB5-1F81-4039-A5DA-FB018EE7ABF5.jpeg Maybe this will help You.
     
    Last edited by a moderator: Dec 23, 2017
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  5. Adrian Mos

    Thread Starter New Member

    Dec 15, 2016
    4
    1
    Bro thanks a lot, this gives me a chance. As a tip, don't buy those schematics you find online, it misses the schematic for the SMPS.

    Btw can you write me what you see on D11 and D10 ?
     
    Last edited: Dec 23, 2017
  6. drops206

    New Member

    Dec 20, 2017
    9
    2
    This is the same diode as D13. Do You check voltage under load? Without main board conected smps on pin 8/9 shows 7.5V. But when i conect board itd drop down to 4-5v.
    The voltage in Yours psu is stable or not? Mine the voltage is floating. 7.40-7.70V

    Do You have that 26 pages SM?

    Roasted IC - OB2279C
    When mainboard is conected do You have ~1V on pin 1 ACC?

    Check the U601 on main board near 9P connector. 3 and 12, and write the value in reply. But this time be more careful :)

    5E12F4EE-1170-496F-8DAD-15B6AEB8C6EE.jpeg
     
    Last edited by a moderator: Dec 23, 2017
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  7. Adrian Mos

    Thread Starter New Member

    Dec 15, 2016
    4
    1
    Last time i've done anything was like an year ago. I haven't checked the ACC pin.
    Give me a day or so to bring it back from the basement and reattach the boosters so i can test it under load.
     
  8. drops206

    New Member

    Dec 20, 2017
    9
    2
    Q1 - JCS12N65FT - N-Channel MOSFET - in 19V rail.
    Q4 - ITA08N65A - N-Channel - MOSFET - in 7.5V rail.

    D2 / D3 - UF1604CT - 16A ULTRAFAST GLASS PASSIVATED RECTIFIER - in 19V rail.

    D7 - MBR2060CT - 20A SCHOTTKY BARRIER RECTIFIER - in 7.5V rail.

    In SMPS for L8.

    I compare it with L16.
    If your tests with another power supply makes the power button is lit up, apparently SMPS is damaged. As I mentioned, I have L8 and L16. the symptoms are identical, but the PSU looks different.
     
  9. drops206

    New Member

    Dec 20, 2017
    9
    2
    OK, its looks different but uses the same mosfet in 7.5V rail ( ITA08N65A ) and diode ( MBR2060CT ).
     
  10. drops206

    New Member

    Dec 20, 2017
    9
    2
    And ofc uses IC OB2279CP :)
     
  11. drops206

    New Member

    Dec 20, 2017
    9
    2
    Today I plug external PSU. Power button lights up. On L8 and L16. The problem is that mainboard needs signal from SMPS (that the device is turned on).
     
  12. drops206

    New Member

    Dec 20, 2017
    9
    2
    Without the signal it will turn off. :/
     
  13. drops206

    New Member

    Dec 20, 2017
    9
    2

    Sometimes the SMPS is only partially working: it may start for a fraction of a second and than shut down, or it may pulsate trying to start every few seconds and shutting down after a fraction of a second, or it may produce a wrong output voltage. Here, probably all power semiconductors are good, so the first thing to check are the capacitors.

    Than, there may be something wrong with the feedback circuit: a good trick is to apply an external adjustable DC voltage to the SMPS output (the SMPS being not connected to the mains). When gradually increasing the DC voltage, you should see the feedback circuit working when you cross a threshold near the nominal output voltage. Since, while doing this test there are no dangerous voltages involved, you can easily use an oscilloscope to diagnose the feedback circuit. You may also have to supply the controller IC (on primary side) with the same low voltage source to see what happens on the other side of the optocoupler.”
    Quote from another website.
     
  14. lpnskumara

    New Member

    Mar 1, 2018
    2
    0
    I have a Power supply issue. 7.5V is working but 24V is not working.Fuse and one FET 20N65 was also short circuited.any body have the schematic for this power supply.

    PCB Number :
    NER-SMP00-284
    L16-SMPS
    Rev : A07

    JBL AUTHENTICS L16 POWER PCB
     
  15. drops206

    New Member

    Dec 20, 2017
    9
    2
    Hi. Please upload a picture of Your smps. Top and bottom side.
     
  16. lpnskumara

    New Member

    Mar 1, 2018
    2
    0
    These are my PCB top & Bottom side pictures 20180307063105602.jpg 20180307063118397.jpg 20180307063136696.jpg
     
  17. ebp

    Well-Known Member

    Feb 8, 2018
    2,042
    718
    In the last photo, about half-way between where the FET was and the IC U1 there appear to be 4 part leads that are unsoldered. Was this done while working on the board?

    It is not terribly unusual for a FET in a switcher to fail, sometimes because the thermal compound has "dried out" and the FET runs too hot. Replacing the FET with new thermal compound is often all that is required. However, the parts that look like they are unsoldered may be part of "snubber" networks that limit the amplitude of narrow high-voltage spikes that are common in this type of switcher (it is a flyback converter). Snubbers sometimes run quite hot and it isn't out of the question that the components melted their own solder.

    That board will be a major pain to fix if you have to replace surface mounted components on the back. They have been glued in place prior to wave soldering. This makes them extra difficult to remove.
     
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