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Sony STR-DB940 help..

Discussion in 'Electronic Repair' started by Ronald, Feb 17, 2007.

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  1. Ronald

    Ronald Guest

    I just got this unit. It powers up and the protection kicks in. I've
    repaired a 840 with this same problem. but it appears on this unit
    the 15 volt regulator gets real hot. I've replaced it already with
    the same results. If anyone has any tips or pointers to where to look
    I'd appricate it.

  2. If the 15 volt reg gets hot, it seems to me there's some IC or other loading
    it down. I'd sub in an external 15 volt or so and see what gets hot.

    Mark Z.
  3. Ronald

    Ronald Guest

    I just got a schematic for it. Traced back to the diodes on the dc
    power board. Gonna replace them tommarow. Odd readings on the
    diodes, in diode test i tested it both ways one reading of 1.1 and .5
    and a few just .5 in one direction. my guess from my repair work on
    pinball machines .4 - .6 is ok diode but could possiable failed
    diode. But I'm replacing them with new ones. to ensure a rebuilt
    power supply.

  4. Ronald

    Ronald Guest

    Follow-up Bump..

    I've replaced the diodes, still no change. I got a schematic off the
    internet. finding a short in the 15 volt line is tough. my thoughts
    if I unsolder the parts in the line it should resolve the short.
    Replace them one by one until the short shows up. Sounds logical?


  5. That's why I recommended subbing in an external 15 volts or so (with the
    unit turned off and unplugged) and see what gets hot. Much quicker and
    easier. Helped me fix many a unit. These pieces are so complicated that
    tracing everywhere that 15 volt line goes would take way too much time and

    Mark Z.
  6. Ronald

    Ronald Guest

    should I tap anywhere in the 15 volt line? chassis ground or pcb

  7. The way I would suggest is to remove the 15 volt regulator (positive 15, I
    assume) and connect the positive lead from the power supply right there or
    at the capacitor which would usually follow. The ground of the power supply
    would connect to chassis ground. If the supply is adjustable, you can start
    at a lower voltage.

    The shorted or leaky part is probably on the DSP board or an input switching
    IC near the inputs, or maybe one or more bad op-amps.

    One thing. If it's really a dead, dead short, i.e. zero point zero ohms,
    then just feeding your power supply into it might not reveal anything, since
    some resistance is necessary in order for the bad part to generate heat.
    This is pretty rare but I have seen it happen. However, your regulator IC
    would probably just shut down if this were the case.

    Mark Z.
  8. Ronald

    Ronald Guest

    With your help we found the short. it in two switching chips... I
    need some help locating them.

    Toshiba TC9273N-004 and TC9273N-013 these both got real warm and
    one let out a puff of smoke :) so we nailed it.

    Thanks for all your help if you have any insites... let me know

  9. <snip.>

    Get the IC numbers off the board and you can get order them from Andrews
    Electronics. Their number is 800-289-0300.

    Also, I have seen the TC9273N-004 from Onkyo cheaper. Not sure about the
    other. Their number is 800-229-1687. They can look up the generic Toshiba
    numbers you gave - at least they've been able to when I called on one

    Mark Z.
  10. Ronald

    Ronald Guest

    Got my replacement parts in no dice. One gets real warm. I'm
    thinking this amp is screwed. I've only put about 30 bucks in parts
    into it. I have no clue what else to look for.

  11. I don't think those chips get warm normally. Could be one of the plus or
    minus 15 volt lines is high. You could still have a blown channel, or a bad
    voltage amp IC...

    Mark Z.
  12. Ronald

    Ronald Guest

    Now when I put the new chips in, I unsoldered the amp transistors all
    of them. I can unsolder the zig zag'd ic's I had to replace one of
    these in my other receiver that had a protection issue. the -15 volt
    line seems stable its not warm. the +15 line is hot to the touch.
    But not scolding hot like it was before. its about the same temp as
    the -15. i can go though and unsolder the ic amps and the transistors
    amps, and unplug the bias's. One thing odd that I noticed. when I
    plug in the tuner module the amp goes into protection mode right
    away. I happen to have an extra module. plugged that in and got the
    same results. Now with these replacement chips I got the Toshiba
    TC9273N-004 and TC9273N-013 I found a toshiba tc9273n-007 this is
    what I replaced them with assuming the pinouts are the same. my guess
    is they aren't . I don't know where to get some information on
    these. I can order the 'correct' chips from andrews like you
    recommend. But thats what I have done so far. Mark I appricate all
    your help! Most people would stop and not bother to help. You
    stick around. :) Thanks for that bud!

  13. The tc9273n-007 would not be interchangeable. These chips are pretty

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