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..
PERCIEVED DIODE IDENTIFICATIONS . . . .
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 . .
VISUAL TECHNICAL REFERENCING . . . . .
https://s1.postimg.org/4lvhuz8665/REFRIGERATOR_BOARD.png
73's de Edd
