Samurai Appliance Repair Man

[Samurai Appliance Repair Man]

#1 It should take 2 leads to make a voltage measurement. Voltage is a measure of potential difference between two points.

Yep!

#2 I’d say no, neutral is not a reference point in a 240 VAC. It’s just present for safety purposes?

It’s kind of a trick question. In this case, although Neutral (which is at ground potential) is not a direct reference, it is an indirect reference. The very quantity of 240 VAC would be meaningless unless we knew what 0 was.

Are we having fun yet? 🤠

[Samurai Appliance Repair Man]

First, you have to understand that all voltages are relative to some other voltage.

For example, there is no absolute 120 VAC “out there” somewhere all on its own. The earth itself has a charge relative to the sun or some other planet. But because we live on earth, we assign a voltage of 0 to the earth. So earth is the reference for all other voltage measurement on this planet.

So when we talk about voltage we’re not talking about voltage at a specific point. Instead we talk about the voltage difference between two points.

As a reminder to us that this is exactly what we’re doing, we say things like “voltage between these two points” or “voltage at this point with respect to (or relative to) some referential point.” Both mean the same thing. In the case of AC voltages, our reference is Neutral which is bonded to ground (earth) in the circuit breaker box. In the case of DC voltage, the reference is DC Ground, NOT Neutral or chassis.

Pop quiz: How many leads does it take to make a voltage measurement? Why?

Pop quiz 2: Is Neutral still a reference when making a 240 VAC measurement (L1 to L2) even though our probe is not on Neutral?

• This reply was modified 1 year, 7 months ago by Samurai Appliance Repair Man.
• This reply was modified 1 year, 7 months ago by Samurai Appliance Repair Man.

[Samurai Appliance Repair Man]

Your topic title says “Module 4, Unit 6.” But Module 4 only has two units. Could you clarify, please?

[Samurai Appliance Repair Man]

Here’s a good training video from Whirlpool explaining PWM signals with inverters. He shows both as oscilloscope display of the PWM signal as well as the reading on a voltmeter. See if this helps:

https://cfvod.kaltura.com/pd/p/1661131/sp/166113100/serveFlavor/entryId/1_s1et7f96/v/1/ev/12/flavorId/1_2i0lsaol/name/a.mp4

[Samurai Appliance Repair Man]

To your pop quiz, I believe we can also test for continuity or voltage from R to OR to check for an open in the control leg.

You win the special prize!

[Samurai Appliance Repair Man]

in the above mentioned case i just need to do IxE=P 13.2X115=1518w on the input and and there i have it!

You got it, Toyota!

[Samurai Appliance Repair Man]

This is a great question, Soo. Good job for thinking about this.

Short answer: There’s more than one way to skin a cat.

Long answer: On service calls, you will have to make decisions about how to test your troubleshooting hypothesis based on the specifics of the situation and your experience with that particular appliance model.

This is a stack laundry unit with the motor and drum right near the area where I need to put my meter probes. I had to make a risk calculation: am I willing to have my hands and meter probes (with wires) near a running motor and rotating drum in a tight space with low visibility and a live circuit so I can make a voltage measurement? Or, in this particular situation, do I instead opt to unplug the unit and do a different measurement (ohms) on a dead circuit with nothing running?

Also, based on my experience with these dryers, I know that if the heating element tests good on ohms, there’s a very high chance that it’s functional under load because these elements do not fail that way– once they go open, they tend to stay open and one end of the broken heating coil fuses with the metal casing. So I knew from experience that an ohms test on this particular dryer model with this particular element type was diagnostically meaningful. But this is wisdom that comes from experience. I may not opt for an ohms test on another type of dryer with a different type of heating element.

In that video, I was also illustrating some basic circuit principles that you’ve learned such as total resistance in a series circuit with more than one load.

Finally I was illustrating how to apply the concept of EEPs to test your troubleshooting hypothesis.

Pop Quiz: What would be another way to troubleshoot this problem? What electrical measurement would you make and where?

[Samurai Appliance Repair Man]

but in general we need OHMS of the coils,

You do not need or care about the ohms of the motor coils. Ohms are only part of the story when it comes to total opposition to electron movement (current). This total opposition to current is called Impedance. Most of the coils opposition to electrons is from Reactance, specifically inductive reactance. This only appears when electrons are moving. Impedance is the vectorial sum of Resistance (ohms measurement) and Reactance.

Ohms measurements only measure the resistance of the copper windings to electrons. This is called Resistance. But Resistance is a minor part of the total Impedance. Most of a motor’s impedance is comprised of Reactance. So ohm measurements are only a tiny part of the Impedance story.

The Horsepower rating of a motor is referring to its mechanical output power. So you can’t use it to calculate the motor’s input wattage or amps because there are losses from input to output. So you need to supply more wattage on the input to get a specific horsepower on the output. The losses show up as heat losses from the motor itself. So ignore horsepower and use the other spec you’re given: FLA.

FLA is full load amps. Since this is an input to the motor, that is the expected amp reading on that motor when operating with a full mechanical load. No calculation required– just measure the amps to see if the motor is operating in spec or not.

Don’t jump down rabbit holes wondering about motor power factor and efficiency. You will never need to do this as an appliance tech. Instead, learn to interpret and apply to the specs that are already given to you. If you want to delve into PF and %eff out of curiosity, that’s great but they are not useful in troubleshooting which is why they are not taught in the course.

[Samurai Appliance Repair Man]

as regards checking the the motor’s amps are power factor and efficiency not supposed to be taken into account?

We don’t need the power factor because we’re not interested in the motor’s efficiency. As technicians, we are only interested in whether or not it is operating in spec. Specs must be given to us. What is the spec we need to know about a motor’s operation in order to assess whether or not it is operating in spec?

as iv been tought by you i tried to calculate the amps by using P/E or wattag by E*I AND the results didnt come out right as stated on this motor’s nameplate.

You’ll have to give a specific example and show your calculations.

[Samurai Appliance Repair Man]

On the third video shows Mr Brown checking digital communications pulses on the receive terminal.Where is the other meter lead located?

Since data is DC voltage (switched on and off at specific rates), the reference will be DC Ground (not chassis, not AC Neutral) as it would be for measuring any DC voltage.

[Samurai Appliance Repair Man]

half splitting a 240 volt heating element is always a live test.

You could half split using continuity testing but this is clumsy and unreliable. Using half-splitting with voltage tests is expeditious and very reliable. And to test for voltage, you have to be working on a live circuit.

[Samurai Appliance Repair Man]

i need to have the techsheet as well as the schematic

Exactly! Now you’re thinking like a tech. For any problem solving, you need to be able to identify what additional information you need to solve the problem. Sometimes, that’s a strategic electrical measurement, sometimes a temperature measurement, sometimes you need the schematic to see how the components get their power supply.

In the case of the Samsung board pinout shown at the time you called out, you need to realize that that diagram is simply telling you what those board pins connect to. But it doesn’t tell you how it connects. So, for example, CN4 & 5 are both labelled Fabric Temperature Sensor. Does this mean there are two sensors? Or does it mean that those pin are the two sides of the sensor circuit? The schematic would show explicitly how this circuit is configured.

This is the type of thinking a technician does every day, all day. It’s both understanding how circuits work AND the technology you’re dealing with. All mental cylinders firing at the same time as you bring your observation and analysis to bear on the problem.

[Samurai Appliance Repair Man]

Technically, the base frequency doesn’t change but instead is modulated by the duty cycle. But your meter picks up the change from 0 VDC to 12 VDC and from 12 VDC back to 0 VDC and then displays this to you as a “frequency.”

[Samurai Appliance Repair Man]

on the first video discussing thermal fuses and hi limit tstats at 16:00 minutes on the PCB pinouts ther are two lines spelling FABRIC DETECTION SENSOR are those the connections to the moisture sensor?
2.why there are 2 conecctions for TEMP SENSOR on pin 3 and pin 7 are they both connected to the same thermistor? or they are 2 separate thermistores for each pin?

I want to help step you through this so you get the thought to figure these kinds of things out.

You can easily answer this question by looking at another document that accompanies the pinout diagram for this model. What other document would you need to see?

3.as regards the moisture sensors on the 2nd video how can you actually test them ? is there any easy straightforwad and practical test for that?

Moisture sensors are just two metal bars set close together (but not touching) so that when wet clothes bridge the gap between them, it completes a circuit that the board is monitoring. They very rarely fail. But some self test modes in some dryers will let you test the sensors by showing you when the metal strips are electrically connected. If not, you can always use your meter set on ohms and probes on each wire from the each sensor bar and see if the reading goes low resistance when you bridge the bars with a wet cloth.

[Samurai Appliance Repair Man]

I use the term liability to mean that IF break or damage something on a service call, you are liable to fix or correct it. Anytime you move an appliance, you are incurring a risk of doing property damage. For example, you could scratch the kitchen floor when pulling out a dishwasher, range, or refrigerator.

In the specific case of dryers, we usually aren’t dealing with nice floors or cabinetry, so I’m mostly concerned about two things: 1) an impossible vent configuration in a laundry cubby where the only way to reconnect the vent is by removing the washer, too. And 2) gas lines that are too short or that use coiled copper where the copper tubing can get crimped. I’m always looking for ways to troubleshoot with minimal disassembly and appliance movement. Usually, that means accessing the control panel to troubleshoot from the control board or timer. You can usually access the control panel with minimal movement of the appliance.

When you do need to move the dryer to complete the repair, be sure you have evaluated the two items above to both plan for the movement AND include any extra work required in your quote for the job.

• This reply was modified 1 year, 9 months ago by Susan Brown.
• This reply was modified 1 year, 9 months ago by Susan Brown.

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