In between the blue relay and the glass fuse…it has white stuff around it…what is this component?
Best guess based on the photo, is it’s a ferrite bead assembly.
Given the location on the PCB it likely is part reference L1 (may be hidden by the supporting caulk).
A working ferrite bead assembly will read as a short circuit on an ohmmeter.
A ferrite assembly that reads open circuit means the solid wire running through the bead has melted (fused). To troubleshoot the rest of the circuit when a ferrite assembly fails, you can replace it with a piece of solid wire.
These devices rarely ever fail after the first year of a products life.
In recent decades, they are primarily used to reduce the amount of electrical interference a device creates.
Thank you very much for the reply. I am troubleshooting a wine cooler that is not cooling…compressor is not getting power…i narrowed it down to either the 120 vac not getting to the load side of the relay, the control side of relay not receiving the correct voltage, and lastly a faulty relay.
Troubleshooting pcbs is brand new to me. Do i just do basic continuity tests to confirm and/or find any breaks in the circuitry?
Excellent! You have correctly identified the three possible sources of the problem. I’ve known professionally trained component level PCB repair technicians with decades of experience who still can’t come up with a nice complete set of potential causes to a problem. They are perfectly fine technicians but often need assistance from engineers to find unusual faults.
Yes, that is the best first step. If that shows no obvious problems, then change to measuring the resistance of the connections/components. On rare occasions a continuity will check indicate OK but the resistance is just a little too high for normal operation (e.g. > 1 ohm on a relay contact).
When continuity/resistance tests do not lead to a solution you’ll have two choices for the next troubleshooting path.
- The safest, but very time consuming, next test option is to remove the relay from the PCB and test it for proper operation.
Because I have the training and decades experience working close to live household AC power for troubleshooting, I’d skip that time consuming test at first.
- Trace the AC power through the circuit.
These are my tips for troubleshooting circuits with AC power connected:
- Work on an insulated bench top and an insulated floor (concrete is NOT an insulator)
- Wear insulated footwear
- When not too inconvenient, connect the test leads with power off, turn power on, take the reading and turn power back off
- If probing with one hand, keep your other hand in your pocket (current flowing between your hands and through your heart is the most deadly)
Now knowing that this is refrigeration device, the mystery device being a small ferrite bead is less likely. It may be an additional circuit protection device or inrush current limiter. However all series connected AC power protection devices can be checked with a continuity/resistance test.
Great. Thank you for the detailed explanation…so I will start with the basic continuity tests…if I am getting 120 vac to the load leg of the relay than I will focus on the relay and try to apply the correct voltage to activate it and see if I get continuity at the load end…
I have a feeling I am not going to get continuity leading up to the load leg. If I do find a break in the line can that be repaired? If so how do I go about that? I can cut through the trace and somehow lay some solder over the area that is broken? I am brand new to all this so excuse my lack of knowledge. Thank you for your time
That is the right idea but instead of just solder for the bridging, use some bare wire over the track as a patch.
I like to scape away a 1/4" (6mm) section of the solder mask on each side of the break, tin the tracks and wire, then solder it in place. If there is only a tiny area suitable for soldering to, I will add an adhesive after soldering to give the wire patch a little extra strength.
For the bare wire I choose a gauge that is just a little smaller in profile than the track is wide. Often for AC power tracks I’ll end up with a short piece of 14AWG household electrical wire for the patch.
When the bare wire is soldered down the repair will be almost as good as a new PCB.
Ok so I tested the power in and power to compressor…they all test good…no breaks…all have continuity…leaving me to bad relay or not enough power being sent to relay…
I test 12 volts on one end of the coil side and the other end of the coil side is reading 6 volts. I don’t know if that side needs to read 0 volts? Or if it needs to read 12 volts…or if in fact the 6 volts that it is reading is correct and I do in fact have a faulty relay…
The voltage across the relay coil should change between compressor on and off states.
Typically the voltage will change from zero for off, to the rated coil voltage for on. However there is actually a valid range for both, a typical range could be <8 for off and >10 for on.
Is there any readable text on the relay body?
That will usually get us the exact specs for this model relay.
Unfortunately nothing readable on the relay…I do hear it click when I turn the unit on and it is 12v one leg and 6 the other…
Now I put a 9 volt battery and doubled it up to get 18 volts…I put it to both coil pins of the relay…heard it click while simultaneously managing to check for continuity on the secondary side of the relay and nothing…I’m starting to think bad relay now and not that the relay isn’t getting the correct voltage
Actually I was able to see the reading on the relay…says 250v 16v 30amps
Your troubleshooting results make me think it’s bad contacts on the relay. So a replacement seems to be needed.
Once you get the relay off the PCB, take photos from a couple sides, let us know about any additional text that readable and what the dimensions of it are.
Hopefully there will me a manufacturers name or logo and part number. If not the dimensions, photos, and already provided text should get us to a suitable replacement choice.
Yeah I got everything I need from the relay itself…found a replacement part…
I just hope the diagnosis is right…I don’t feel 100% I only feel 95%…I want to really understand this better. .
If it is a 12 volt relay then is 12 volt needed just on one end of the coil leg? Am I reading 12 volts on one end and 6 on the other because of the natural resistance from the coil winding? I get 265 ohms of resistance when I measure that…I would love to know the answer to this. I’m just so confused as to how the relay even gets the 12 volts…I hate to GUESS I like to KNOW
I don’t even know why anything is connected to the other end of the relay…you would think all you would need is power getting to one pole of the relay and the other side doesn’t need anything but maybe it needs to get grounded?
What is the manufacturer and part number for the relay?
The manufacturers data sheet for the relay will help me figure out a whole lot more about what your observing electrically.
Without the schematic diagram for the circuit we can never be certain that we can actually fix this. Even with the schematic, the failure can turn out to involve many parts making it not cost effective to repair.
A 12V relay is designed to operate with a nominal voltage of 12 across the coil. But as previously mentioned the data sheet will specify a maximum and minimum voltage range for proper operation.
Yes the coil resistance, combined with the impedance of the driving circuit, is what creates the voltage drop. It is all related with a single multiplication.
Volts = Amps times Ohms.
The volts in the equation is the difference in voltage between V+ and V- terminals of the coil.
In this case we’ve got 6V and 265 ohms, so dividing 6 by 265 equals about 0.023 Amps.
The relay has a specification for the minimum current needed to turn on, and also the maximum current it can survive. The designer can pick a value in the range that provides the desired performance/price compromise.
One end of a relay is often grounded. In old style automotive applications one side is literally bonded to the chassis and you’d definitely read 0V on that side.
In modern electronics, most often the normally grounded side of the relay is actually driven with some circuitry and the positive side is directly tied to V+.
To keep the relay off, the circuit holds the normally low voltage close to the V+ voltage of the relay. This prevents any current from flowing through the coil. To energize the relay the circuit brings the voltage down on the low side of the coil causing current to flow. The current makes the relays’ electromagnet pull the switch contacts to their on positions.
When the circuit drives the relay coil down it is usually to within 1V of ground. However to save costs a designer of a consumer grade circuit can let that end up higher as long as it meets the relay manufacturers spec.
The Wikipedia article for relays is a pretty good introduction to the general concepts.
sanyou smih-s-112lm
Sanyou is the manufacturer…
I traced the side that I read 12v from and it definitely is attached to a 12v source…when I trace the side I only read 6v from it doesn’t look like it has any sort of power going to it whatsoever…so I guess the 6v that I am reading is simply the voltage drop across the coil.
Thank you so much for the replies. You have helped me a lot
Found the data sheet
The voltage requirements are:
Max allowed 130% of nominal (15.6)
Worst case turn on voltage, 80% of nominal (9.6)
Worst case turn off, 5% of nominal (0.6)
It shows the minimum voltage for guaranteed operation is 80% of nominal you measured 50% of nominal, way out of spec.
If the replacement relay doesn’t work, it means the driving circuit has a fault. Often the driving is done by a transistor of some sort. Ideally the driver circuit will be designed to switch the voltage measured across the coil (not to common) from >=9.6V when on to <=0.6V when off. The following page describes all the common relay driver circuits. https://www.electronics-tutorials.ws/blog/relay-switch-circuit.html
If the replacement does work, and the voltage across the coil is >=9.6 everything is good. If the voltage across the coil is <9.6 that could be the reason the relay failed at this point in its life.
Thank you for doing all this research for me. You are going above and beyond.
So the 12 volts I read at one end of coil is right on the money and I can track it back on the board to a 12v power source. However when I track the other leg back I don’t see any type of power source at all. Almost like it is going back to ground.
I an getting 12 volts on one end of coil (which I guess is perfect) and on the other end I’m getting 6 volts (which is out of spec)
Part I’m confused about is where is this voltage coming from on the side I’m reading the 6 volts from? I track it and can’t find any source of power at all…when I track the side that does get 12 volts I can clearly see that it connects to a 12v power source. This is why I was thinking that the 12 volts to 6 volts was just simply a voltage drop occurring through the coil windings…
There is no way a directly connected 265 ohm load (the relay coil) can have anything other than V+ and V- (12V & 0V) on its terminals. To have a different voltage there must be circuitry between the coil and the power connection.
For information on why, see the two references at the end.
The low side must be connected via a PCB trace or wire to a driver circuit of some kind for the low side to read >0. Possibly the trace is in an internal PCB layer so invisible.
At a minimum, to make the low side of the coil read 6V with 12V applied, a 265 ohm resistor from the low side to ground is needed. However it is more likely driven by something else.
Further reading:
Will read and study those too…265 ohms is the exact resistance I measure from low to high side if coil…maybe I mentioned that before…my head is still spinning…going to study this some more…thank you
That’s where I got the value from (data sheet says it’s 267 +/-10%)
There’s a possibility that if you measure resistance from the coil low side to a ground connection, it will also read 265. Two equal value resistors divides a voltage in half.
Also try swapping the resistance meters’ leads around and see if the resistance is different (semiconductors in the path will make the the meter act that way).
It’s also possible that a driver circuit that does the function of making the coil act like there is 265 ohms to ground, will not show 265 ohms on a resistance meter.
Most importantly have fun doing this, because it rarely makes economic sense to do repairs like this.
I guess I need to do a little more testing on the other side of this coil (the bad side that only tests 6 volts)…
I only found continuity on one other pin when testing that side…I will try to track it…it does have a lot of components near it labeled Q6…c8…r15…guessing these are capacitors and resistors…not sure the Q one…is there a way I can just simply test all the different components? Certain type of test for capacitors…resistors etc with a basic multimeter?