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Technics SA-G90 With "Overload" message.

Discussion in 'Troubleshooting and Repair' started by Rick79, Aug 19, 2016.

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  1. Rick79

    Rick79

    283
    5
    Nov 26, 2014
    A friend of mine said the repair shop guy he took the receiver to said that he don't touch these kind of receivers. I'm guessing because the parts are outdated or because the repair is more than what it's worth.
    I already have something I'm working on, but I just started taking it apart thinking I might get lucky and just find cold solder joints. Right away I noticed a burned spot on the back of the board, it's a burned up resistor, R672 in the photo.
    Did this resistor just give out from being hot all the time or did something cause it to overheat? I was thinking about replacing it with a new one, but I can't find the schematics online to find out the ohms rating
     

    Attached Files:

  2. dorke

    dorke

    2,342
    665
    Jun 20, 2015
    Is this model SA-G90,the correct one?
    Google doesn't find anything like it.
     
    Rick79 likes this.
  3. Rick79

    Rick79

    283
    5
    Nov 26, 2014
    Yeah. I can't find anything either
     

    Attached Files:

  4. dorke

    dorke

    2,342
    665
    Jun 20, 2015
    You may get help from Technics-US here
     
  5. Rick79

    Rick79

    283
    5
    Nov 26, 2014
    OK. Thanks
     
  6. 73's de Edd

    73's de Edd

    2,999
    1,261
    Aug 21, 2015
    .


    Sir Rick79 . . . . . . .

    Can you trace its connections and see if one of . . .or both . . . leads of R672 might lead to the 26 pin wide but skinny IC 601 or 602 . . . .RSN3305P power I.C.'s ? . . . . . costing $84 a copy.
    If so, going to what pin(s) number.
    Also check out all of their solder joints . . . .VEWY-VEWY . . . . cawefully.

    Consulting another different SA-G76 unit . . .yet . . . . that still uses the same series of potted A,F.output modules
    The parts list for all of the R600 series 1 watt film resistors only shows (2) 100 ohm value units listed.
    600 numbered series resistors seem to be assigned to the power output stage, while 700 series numbered resistors seem to be assigned to the regulator circuitry.


    Also . . .if it reads open . . . . use the ohming of a VERY lightly exposed scraping at the CENTER of the resistor, to
    see if either end, will still give a reading of that resistors half value. Metal film resistors are very good at still retaining their values . . . . .even after glowing at a dull red overdrive.



    73's de Edd



    .
     
    Last edited: Aug 22, 2016
  7. Rick79

    Rick79

    283
    5
    Nov 26, 2014
    On the board of this unit it is IC651, a 22 Pin RSN313H25
    R672 reads .311 ohms and is connected to the 19th pin.
    R671 the resistor next to R672 reads .555 ohms and its connected to the 18th pin.

    Does this mean that IC651 is blown?
     

    Attached Files:

  8. Rick79

    Rick79

    283
    5
    Nov 26, 2014
    I haven't heard from them. I wonder if the IC is blown out.
     
  9. 73's de Edd

    73's de Edd

    2,999
    1,261
    Aug 21, 2015
    Sir Rick79 . . . . .


    You say . . . .
    On the board of THIS unit IC651, is a 22 Pin RSN313H25


    R672 reads .311 ohms and is connected to the 19th pin.
    R671 reads .555 ohms and its connected to the 18th pin.
    ( R671 is the resistor next to R672 )



    Here is your missing info that you need to further evaluate your potted power module..
    The top is the schematic of its wiring interconnects, while the bottom is the explanation of the units internal building blocks.

    You say that the REAL damaged resistor is R672, but with there being a lesser degree of damage to R671 also.

    The HEAVY + and - supplies initially feed pins 1 and 2 for the internal POWER transistors and then branch over to the left to your R671-R672 to feed in the + and - supplies of the power driver stage, after passing through your series "problem" resistors.
    Probably not much of a chance, but there are two electrolytics that bypass to ground after those two resistors. (YELLOW box marking)
    The most telling test would be to take meter in hand and place in ohms function and a low range and use pin 8 as ground reference and see how low the ohmages of pins 18 and 19 are reading.

    Note I said OHMS function . . .as the earlier low readings that you gave were likely in diode test mode.

    You say . . . .
    I wonder if the IC is blown out.


    I am HEAVILY thinking that it will test as being low ohmically shorted internally.

    I see that a replacement down in the $18 range is available, if you look for it.

    PIN OUT AND FUNCTION BLOCK REFERENCE:

    Technics RSN313H25.png


    73's de Edd
     
    Last edited by a moderator: Nov 8, 2016
    Martaine2005 likes this.
  10. Rick79

    Rick79

    283
    5
    Nov 26, 2014
    Thanks!
    The lowest ohm setting on my meter is 200 ohms. I don't get a reading for pin 18 unless I set the meter on diode mode and I get 1.188

    For pin 19, meter set on 20k I get 2.16
     
    Last edited by a moderator: Nov 8, 2016
  11. 73's de Edd

    73's de Edd

    2,999
    1,261
    Aug 21, 2015
    Looks like you need to solder suck / solderbraid free, those two resistors, to get out of circuit along with those two electrolytics and set them safely aside.
    Then testing out of circuit, one of the resistors should ohm out as open, while the other one is waaaaay up in its current value.
    Also the electrolytics to test but I don't think either will be dead shorted.
    That then leaves the #18-19 terminals floating . . . . to test against that #8 ground reference.
    Before, you got a reading in the diode test mode, on one terminal, and should again since you are reading semiconductors internally tied into that terminal.
    The other terminal might read the same, but the meter probes may have to be reversed due to the polarity of mirrored semiconductors on that section.

    73's de Edd
     
  12. Rick79

    Rick79

    283
    5
    Nov 26, 2014
    OK, R671, R672, C672 & C671 are off the board now.
    R671 reads .526 with meter on diode mode
    R672 reads .318 with meter on diode mode
    I can't test the Capacitors because I don't have a capacitance tester.

    With meter set on Diode mode...
    Black probe on Pin 18 with red probe on pin #8 I get .752
    Red probe on pin 19 & black probe on pin 8 I get .628
     
  13. 73's de Edd

    73's de Edd

    2,999
    1,261
    Aug 21, 2015

    R671 reads .526 with meter on diode mode
    R672 reads .318 with meter on diode mode


    The idea there was to test resistance in OHMs function.

    I you don't get a valid reading while testing those two, through all of your ohms ranges, consider a possibility of a damaged OHMS functionality of your instrument.

    Seeing that your meters OHM ranges are 200 ohms ---2K---20K---200K---2 Meg and 20Meg
    To somewhat confirm the units functionality, look around the board and locate different resistors about half value of each of the different ranges and test and confirm if they read close to that on each range..


    I can't test the Capacitors because I don't have a capacitance tester.


    The consideration there was to merely check for them having a low resistance or short when testing in OHMS mode . . . .not diode mode.
    I'm not really expecting that, however.
    I'm really expecting "crashed" power semiconductors within the RSN313 potted module.


    With meter set on Diode mode...
    Black probe on Pin 18 with red probe on pin #8 I get .752
    Red probe on pin 19 & black probe on pin 8 I get .628


    That testing also needs to be in OHMS mode of testing

    My personal last analysis would be to place 2 "sacrificial " 47 and 82 1/4 watt carbon film resistors in place of the old ones and plug in, turn on and watch, with power cord in hand to yank.
    I'm FULLY expecting those to turn into their forerunners, indicating the need of a new 313 potted module.

    73's de Edd
     
  14. Rick79

    Rick79

    283
    5
    Nov 26, 2014
    OK I thought I read you saying to test them in diode mode.

    R672 gets readings in 200k, 20k & 2k
    In 2k range I get .310
    R671 gets readings in 200k, 20k & 2k also.
    In 2k range I get .553

    I'm gonna put this Receiver aside till I can afford the 313 module, or unless I find a donor.
     
  15. bugler13

    bugler13

    1
    0
    Nov 8, 2016
    Hello,

    Incidentally, I have exactly the same problem on Technics SA-AX540. The R672 (47 ohm resistor) connected between pins 2 and 19 is burnt. With R672 removed, I measure -31V at pin 19 & 3 which confirms the IC651 (RSN313H25-P) is probably internally damaged. IC651 is the output amplifier for the surround channel, while IC601 is for the front and centre. Sound effects (e.g., surround, sfc) does not work with damaged IC 651.

    In short, IC651 is internally damaged but receiver will still work with front and centre channels with no sound effects.I will report back if I find any surprises.

    Cheers

    Terry from Vancouver Canada
     
    Last edited: Nov 8, 2016
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