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Component recognition

Discussion in 'General Electronics Discussion' started by Gang_wheell, Oct 16, 2017.

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  1. Gang_wheell


    Oct 15, 2017
    Hello ,can anybody help me to recognition this component?label is 18RKG4[​IMG]
    the component is from temperature control board from fridge i attach image and position
  2. kellys_eye


    Jun 25, 2010
    It's an 18Ω resistor. Have you tested it?

    Looks to be about 5W or 7W and may even be of the 'fusible' variety.
  3. duke37


    Jan 9, 2011
    Is that a helical wire? If so, it is could be a very low value resistor.
  4. Gang_wheell


    Oct 15, 2017
    thanks for answer i can't test it because its damaged... i try to replace it with 18Ω 2W and 4W but don't work...
    i tested other components and there are ok,maybe i need scheme for this board ,but don't know where to find it?

    i found this site and here was write this label is transistor
    Last edited: Oct 16, 2017
  5. kellys_eye


    Jun 25, 2010
    The resistor doesn't 'blow' without a reason. Something caused it to go dud. Have you found out what?
  6. davenn

    davenn Moderator

    Sep 5, 2009
    well you know that isn't what you want cuz you need a resistor ;)
  7. Gang_wheell


    Oct 15, 2017
    yes i found one zener diode and capacitor damaged i replace them ,but don't know which resistor replace 18RKG4
  8. davenn

    davenn Moderator

    Sep 5, 2009
    did you not read post #2 by kellys_eye ?
  9. 73's de Edd

    73's de Edd

    Aug 21, 2015
    Sir Gang_wheell . . . . .

    CONCEPT of DESIGN . . . . .

    However, in this case you are severely limiting that by ONLY submittintg the components side views of PCB's.

    Your power supply is contained within the very central area of the frontal daughter PCB that is being flipped over and supported upwardly by the 8 elevated wire interconnects.
    Of those 4 side-by- side supports on the PCB's left side, two would be suspicioned of carrying in AC line power for the PS section and with the other set of two, carrying switched relay AC power, out to the units compressor.

    Looking on over to the main board. . .looks like the :
    • 4049 Hex inverter . . . . . might be associated with all of the display LEDs that the unit is using.
    • 4093 Quad Schmitt Triggers . . . . . might be associated with piezo beeper pulse with a driver in the form of the RED STAR transistor..
    • LM324 Quad op amp linears . . . . . be associated with temp and / or thresholds sensing.
    Then, going back to the daughter board with its sole . . . .
    • MC 15541 Op amp linear . . . . .it also could be asssociated with the above temp and / or thresholds functions as was just noted..
    OBSERVATIONS . . . . .

    A side referencing of the power relays numbering . . . suggests the of use of a 24VDC coil so as to permit a hefty spring action to assure a very SOLID snap action in relay switching.
    The WHITE cased poly cap is chosen so that the capacitance reactance is creating an AC voltage drop, with it creating MORE than the required AC voltage needed, when being under the systems prescribed loading.
    That then permits using an additional series inserted power resistor to then trim in and lower the voltage down to the level needed.
    The cap creates a stone cold voltage drop, while the resistor is being so ratiometrically staggered / related . . . by each units proportional voltage drop . . such that it then only creates minimal heat.
    The resistor also provides a bit of input voltage surge cushion at initial AC voltage plug in as well as after a power outage drop.

    Additionally, I suspect the BLUE DOT item to be a MOV, used for power transients or quick surges, and the GREEN DOT 470K to be establishing a light electrostatic grounding.
    That only leaves the two other nearby parts, being the LIME GREEN as a back EMF damping diode across the relays coil.
    That series connection of the PURPLE diode -resistor pair is perceived as being used as a snubber across the compressor side of the POWER relay contacts to abate arcing and contact erosion on the relays breaking circuit.

    Next . . . the Full Wave Bridge creates your DC power from the AC dropped by the res cap pair, covered earlier.

    No driver transistor for the RELAY coil was seen; so it must be the far right YELLOW STAR transistor and routes its collector path along the board edge, back to the POWER relays driver coil..


    All of the BLACK cased units, I expect to be common 1N400x series power diodes.
    All of the glass cased diodes I expect to be small signal 1N 914 /or/ 1N4148 units.
    That is just now leaving a BLUE RECTANGULAR marked diode in the center of the Main board, to read and see if it is probably also being a 1N4148.
    Then there is a cluster of 8 probable other 1N4148's being at the very right end of the board, and also 2 sets of two at the top left corner of the Main board.
    Moving to the daughter power supply, the MAIN suspect of being a power zener diode is the PINK RECTANGLE marked diode
    And at the end of the board, near its sole IC, is a painted M-- (Motorola) with my YELLOW RECTANGLE marked around it, also suspect for being a zener to create yet a sub-sub power supply voltage..

    POWER FLOW . . .

    I perceive of reduced AC power being achieved via the 18 ohm and Series WHITE Poly cap and cap and going to the YELLOW terminals of the FWB rectifier . It has its BLACK DOT negative connection and its RED DOT positive pulsating DC output that gets routed initially to the Main filter storage capacitor RED DASH, being the closest to the GREEN POWER relay.
    That voltage then gets routed back thru the GRAY metal film dropping resistor . . . . ( see the PCB discoloration ) . . . it has been DROPPING . . . . and the the power zener in PINK reduces and regulates down to a lower power supply voltage.
    My suspicion is for the highest initial voltage on the first cap RED DASH to be in the 24VDC range.
    This now reduced voltage supply gets filtered by the second RED DASH capacitor to somewhat less than the 16VDC . . . . as is marked on its side.
    Check the, just off right center, two tandem . . . side by side . . . RED DASH capacitors for their voltages.
    You then have two sets of two stand off leads nearby, with a possibility of two of them carrying + and - connections of power to the Main board, and the other two for handshaking signals between the two boards.

    PREPARATION . . . . .

    Take a BLUE Fine Sharpie and mark on the FOIL SIDES of the daughter / PS board with use of rectangles enclosing diodes leads,
    Also, rectangles for enclosing transistor leads and ovals around electrolytic caps with polarity marked on . . possibly do the FWB also.
    DO duly note that I put your GOOD "bad" resistor back in circuit and even used some translucent TEFLON sleeving on its re- tinned leads (FULLY meeting NASA tech brief 1154) . BUT you just GOTTA stop melting relay case corners with your soldering iron.

    Troubleshooting . . . . .

    Clean out solder from the standoff stake wires and flip the daughter board over and line up the 8 wire stand off interconnects and solder up.
    Power up and see if AC voltage is present at the YELLOW FWB inputs. Then go to DC mode and see what DC voltage you have at the main left filter (give us elect caps voltages and their ufd values).
    Then test across the right filters DC voltage to see what it is regulating down to.
    Then the side by side two cap set to the right.
    Then the PAINTED diode . . . it's likely a zener for a lower voltage sub supply . . . its located over beside the suspected YELLOW STAR relay driver transistor.

    Now you should be able to hold your meter ground to the FWB black connection and use the RED meter probe to see if there is voltage present when you reach down to the 10 ufrd and yellow 22 ufd capacitors on the Main board.

    Stopping for feedback to see your progress . . . . or if in need of further queries . .



    73's de Edd
    Last edited: Oct 18, 2017
    twister likes this.
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