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Resistor Value.

Discussion in 'General Electronics Discussion' started by HellasTechn, May 26, 2018.

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  1. HellasTechn

    HellasTechn

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    Apr 14, 2013
    Hello !

    Could someone please tell me the value of this resistor ?

    Colours right are : Brown, Black, Gold, Brown.

    The DMM reads 30.1Kohm but the resistor is slightly deformed and i am not sure if the value has shifted.

    THANKYOU.
     

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  2. 73's de Edd

    73's de Edd

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    Aug 21, 2015
    Sir Constantine . . . . .

    That's strange . . . . as it Fotie-grafs as . . . . GREEN-BLACK-BLACK-GOLD-BLACK.
    Can you do a light central area paint scraping and then read from either lead end to center point . .
    or quarter point and then get an ohmmic reading, to then use that to interpolate the suspected full resistance.

    73's de Edd
    .....
     
  3. HellasTechn

    HellasTechn

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    Apr 14, 2013
    Will do !

    P.S.

    with a magnifier glass it shows Green, Brown, Black,Gold, Brown. It is the camera that makes brown look like black.
     
  4. WHONOES

    WHONOES

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    May 20, 2017
    The gold band indicates a multiplier of 0.1. Green = 5, brown = 1 so, your resistor should be 0R51. The brown band is for tolerance of 1%.
    Edit: forgot the black band. Doesn't change the value though.
     
  5. HellasTechn

    HellasTechn

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    Apr 14, 2013
    after doing so, it is impossible to get a steady reading and now from one lead to the other the dmm measures 30Mohm...
     
  6. HellasTechn

    HellasTechn

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    Apr 14, 2013
    well... this resistor came out of this power supply.
    https://www.circuittest.com/s-60-12-ac-dc-power-supply-60w-12vdc-5a.html

    I can not find a circuit diagram... :(

    On the circuit it is marked R18
    at first i thought it was a 220Ohm resistor and replaced it with a 220Ohm. wen pluged in the resistor burned instantly.
    Then i checked it again with the dmm and got the reading of 30.1K and replaced it with a 33K. then it overheated and exploded an output capacitor. i know that what i say make no sense without a diagram or a photo. ill upload photos...
     
  7. HellasTechn

    HellasTechn

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    Apr 14, 2013
    the resistor in question is connected as follows. one lead to the optocouplers pin1 (the one with the mark) and the other goes to the outputs positive side and then through an other resistor to the tl431 regulator.

    picture 1 shows the board. in red is the resistor and the blown cap. in yellow are components i found damaged and replaced them.
     

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  8. 73's de Edd

    73's de Edd

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    Aug 21, 2015
    Sir Constantine . . . .
    Your initial repair must have had some serious damage by the looks of the parts which you replaced .
    Does it now pass the initial power up test, when using a 60 watt lamp in place of the fuse?
    What is the identification of the heatsinked special power IC being seen at the top of the unit ?
    The physical position of your resistor suggests that it typically would be used as a current limiting resistor associated with the LED within the optical isolator.
    That would only be a 20 ma drain from the secondary / cold side of the power supply at the bottom right corner.
    Can you trace and draw us a mini schematic of only the connections to parts that are associated with that resistor.?
    Were any of the diodes shown that you replaced, being Zener diodes ?
    Did you scrape the resistor paint coating not hard enough , or did you scrape it TOOOOOOO hard?


    73's de Edd......
     
  9. HellasTechn

    HellasTechn

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    Apr 14, 2013
    Yes indeed but im not sure if it was due to output short circuit or power surge. Short circuit most likely.

    Its a 2sc3679

    Im not sure how to do that. could you exlain to me ? The way it is right now it either blows the resistor (the 220Ohm resistor) or overheats and blows output capacitors when i placed the 34Kohm resistor. The output capacitors are 2200uf 25V and 1000uf 25V.

    Yes i can.
    No they are 1n4004. The diode above is a zener diode and appears to be working when checked with my Huntron Tracker 2000. It gives the correct signature.

    I beleave not too hars or too soft either. i will try removing some more paint.
     
    Last edited: May 27, 2018
  10. HellasTechn

    HellasTechn

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    Apr 14, 2013
    Here is the diagram.
     

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  11. 73's de Edd

    73's de Edd

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    Sir Constantine . . . . .

    Looks like your unit circuitry is just a POWER oscillator that drives the transformer , and uses no IC's.
    It's probably using that other single small signal bipolar transistor in assisting in clamping down the base drive level to the power output to regulate the overall power output.
    I mentioned the use of the series lamp to keep from blowing the output transistor again.
    If you have made the supply come up . . . . without blowing up . . .excluding that " special resistor " . . . you might disregard the precautionary power limiting safety lamp..

    Figure that " THE R18 " resistor function is for voltage dropping for the power to the LED enclosed with in the 817 family of optical isolator.
    And . . . . that you have had one burnt up and also the the follow up guesstimate that you installed.
    In a no power plugged in state, test the LED inside of the 817 to see if any semblance of a LED is still inside, or it is now being just a fused together blob of semiconductor material, now reading as a dead short.
    OR . . . . you might possibly get a diode test result, somewhat akin to 2 series arranged diodes.
    If the later suggests that a LED might still dwell within, then lets initially use this procedure, where you cut the line at RED X . . . . OR . . . just don't have the R18 resistor installed.
    Then you do DC voltage monitoring across any of the filters of the 12v DC output, and then power up the unit JUST LONG ENOUGH to see what level of now unregulated volts shows on the meter . . . .15---18----20 ?

    To keep this low voltage / cold supply side, still all isolated and safe, get a 9V transistor type battery, and use 2 flying wire leads, to connect battery + to a 470 ohm 1/2 W resistor and a lead to the other - terminal of the battery.
    Your free end of the 470 resistor is going to connect to the pad of old R18 that went over to the 817 optical isolator.
    Your batteries free flying lead will be held in hand to be temporarily touched to the negative power output terminal of the power supply.
    If all is well in the 817 and the HOT side of the power supplies regulatory circuitry that that 817 phototransistor feeds, there will be a decrease in power supply output voltage, that you had read before, while holding that connection, just after powering up, for a short time needed to monitor the output voltage again.
    This time it could be down to 9? 7? volts, but rise just as you lift the wire for the battery supplied LED power.

    If this passes regulation control in this manner. . .then I will tell you how to evaluate the sets 431 existing feed back circuitry, to see if it is working..
    If it doesn't, start looking for a common 817 OI as most computer power power supplies use, and u might have 1 in Le JUNQUE BOXE.

    SCHEMATIC REFERENCING . . . . ..

    upload_2018-5-29_3-17-37.png

    73's de Edd
    .....
     
    HellasTechn likes this.
  12. duke37

    duke37

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    The mains comes in top left and is rectified by BR1 and the negative side is earthed. This will give a short circuit.
     
  13. HellasTechn

    HellasTechn

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    Apr 14, 2013
    Where ?
     
  14. duke37

    duke37

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    Just below BR1.
     
  15. 73's de Edd

    73's de Edd

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    Aug 21, 2015
    I only selected that schematic, because it had so much in common with what he is working with.
    FOR THE CIRCUITRY TO THE RIGHT OF THE SM POWER TRANSFORMER AND THE RIGHT OF THE OPTICAL ISOLATOR.
    That is not my draw, and the only fault, I see is that who ever drew it used the familiar ground symbol in two places on the left side HOT supply.
    Better that he used the RED triangle ground symbol and additionally designated as being a HOT grounds that have to be kept isolated..
     
  16. HellasTechn

    HellasTechn

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    Apr 14, 2013
    I apologize for not writing back all theese days. I am "flooded" with other issues and it may be a while before i can work on that PSU again. I will get back to you in the near future. Just need a little time !

    THANK YOU !
     
  17. HellasTechn

    HellasTechn

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    Apr 14, 2013
    Are you sure it is not a 5,1 Ohm resistor ?
     
  18. HellasTechn

    HellasTechn

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    Apr 14, 2013
    The huntron tracker 2000 indicates that the led within is in good state but when i compare the signature of the transistor side with a known good one it gives me different signature...
     
  19. HellasTechn

    HellasTechn

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    Apr 14, 2013
    I forgot to mention that while powered on the PSU makes a loud clicking noise. Now with the resistor removed the DMM could not give a steady reading. Withing 5 seconds or so the output capasitors get very very hot and if powered on for about 10 sec they start to pop.
     
  20. HellasTechn

    HellasTechn

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    Apr 14, 2013
    So do i start looking for a new opto ?
     
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