Forum Replies Created
-
AuthorPosts
-
Hi Sean, some of the schematics on Samsung fast tracks are badly pixelated. I’ve complained to them about this and they say they are going through and updating them.
Post the link to the fast track at Appliantology so I can download it and take a look.
March 20, 2019 at 10:31 am in reply to: Introduction to troubleshooting (analytical Decision) #15589how do you explain that to the customer?
I typically say something along these lines: “I’m a professional technician. When a technician tests a component to see if it’s “good” or “bad”, what we’re really testing for is whether or not the component is operating within the manufacturer’s specifications. We have no other way of determining “good” or “bad”. So if a manufacturer omits key specifications we need to determine whether or not a component, such as a control board, is operating correctly, we have no way of analytically determining if the component needs to be replaced or not.”
Intuition and guesses are not part of my technician toolbag– these are the stock tools of parts changing monkeys.
As Susan mentioned, this does not happen often (fortunately) and Whirlpool is by far the worst offender, omitting key specs we need to determine if a board is sending a data signal, DC supply, etc. I show some of the more egregious examples of this in the Advanced Troubleshooting course– all Whirlpool dummy diagrams as I call them– these look like schematics but they’re really just drawings with lines connecting to boxes with no specs. Utterly ridiculous and also a good example of how far the general skill in the trade has deteriorated: Not only do most techs never realize the omission, but apparently even the corporate techs at Whirlpool didn’t think it was important. This tells you alot about what’s going on in-house at Whirlpool. I have seen some encouraging signs that they are upping their game in some more recent schematics I’ve reviewed.
Just say that you’re currently enrolled in the Fundamentals course and give your MST username. You’ll also need to include your Appliantology. Note that Appliantology is a separate website with separate login.
Reload the page and see if it shows up. Sometimes there’s a sever glitch. Should be at the bottom of the form. The form is hosted by a third party and is very reliable, we get lots of submissions from it everyday so I know it works and works well. If you’re still not seeing it, post a screen shot.
Go ahead and submit the form to request a free limited tech membership at Appliantology: https://appliantology.org/blogs/entry/1010-free-tech-membership-at-appliantology/
Then get certified in Fundamentals request an upgrade to MST Alumnus (a premium membership).
Wait a bit on buying the specialty tools unless you get a job that absolutely needs one. Get the calls rolling in and buy them as you need them with extra cash. Or look for them used on Ebay.
That’s what Appliantology is for— getting into specific problems, specialty tools, techniques, business aspects, etc. It’s ongoing peer to peer support on all aspects of being a professional Appliantologist.
What if I will be on the job by myself and will work by myself in general and it will appear that second person is needed for help. What would you do in that case?
That will indeed inevitably happen to you. In my case, I take one of my sons with me to complete the job. You may take a friend or make use of various devices available out there to help with these types of situations: all Dolly, air sled, etc.
Did it ever happened to you when customer did not describe exact problem properly and didn’t give you an exact number of appliance? How did you go about that?
Probably only about every other call! LOL. We always verify the model numbers that customers give us before we actually go out. If the model number is incorrect, we will contact the customer and they need to give us a correct model number before we will go out. The whole purpose for getting a correct model number in the first place is precisely so that you can pull technical documentation on the appliance to prediagnose it.
To a large extent, you are doing that already by taking the Fundamentals course! That is not a flippant reply, that’s a serious answer.
One of the practices that we teach and encourage is pre-diagnosis. This is where you will pull the service manual and tech sheet for any upcoming service calls and wargame them against the problem reported. The idea is that if there are any particular disassembly procedures that may be needed, you can have them bookmarked on the PDF so you can jump to them quickly during the service call.
Unlike electrical problems, mechanical problems are usually visual, meaning you can observe the mechanism, see how it works, and how it’s failing. You don’t need a course for that, just mental alertness, paying attention to details, and observation.
Miele, Dacor and other brands are no harder or easier to service than any other brand. In fact, all appliances work pretty much the same way-manufacturers are not inventing new technology for their appliance models. Everybody is pulling technology off-the-shelf and adapting it to their products.
What does vary among the brands however, can be details of disassembly, part configurations or specifications (but not technology), etc. This information would be available to you through the service manuals and tech sheets. That’s where Appliantology, your indispensable tech support resource, comes in handy.
The question that I have Is if you have two or more thermistors within the same machine and obviously the same brand will one be used in the freezer and another used in the fresh food. Or are each thermistor different.
Hi Samuel. It depends on the brand. For example, with Samsung, all thermistors “inside the box” are exactly the same. I know that because they tell me that in their tech data. But that does not mean the same thing is true for Whirlpool, for example. You need to either be able to compare the specs on the thermistors you’re going to replace or have the manufacturer explicitly tell you they’re identical. Can not assume they are because sometimes they are not.
Also, typically, when you’re replacing a thermistor, you’re going to be ordering the OEM part number based on the model number, so you’re going to be getting the correct part.
Every 120 VAC load will have two conductors for the power supply: Line and Neutral.
Every 240 VAC load will also have two conductors: Line 1 and Line 2. In the case of a 240 VAC circuit, there is no Neutral.
In any circuit, the electrons change their direction of movement as a result of the voltage polarity in one conductor changing with respect to the other conductor. That is what moves the electrons– they will always try seek a relatively more positive charge and move in that direction. Voltage drives current (a directed stream of dumb electrons).
In a 120 VAC circuit, the polarity of the Line conductor changes twice every cycle, positive on the positive half cycle and then negative on the negative half cycle. With a frequency of 60 cycles per second (Hz), this means the polarity on the Line conductor changes 120 times a second. The polarity of Neutral does not change because it is tied to ground. When the Line conductor goes positive, it pulls electrons from the Neutral side. When the Line polarity goes negative, it pushes electrons to the Neutral side.
The same thing happens in a 240 VAC circuit. The difference here is that L1 and L2 are both changing but in opposite directions at the exact same time. So when L1 goes positive, L2 is going negative, and vice versa. The bigger voltage difference between L1 and L2 (240 VAC) moves more electrons (creates higher current flow) than between Line and Neutral (120 VAC). We see this in Ohm’s Law: I=E/R. If R stays the same and you double E, you will double I.
January 16, 2019 at 10:18 am in reply to: Testing motor windings on a single phase asynchronous motor #15167the problem i’m having is figuring out where the common terminal is located on a dryer motor for example.
“Common” is defined as “common to both run and start windings” and you get this from the schematic, as in the one Sam posted above.
Electrically, that dryer motor works the same way as a hermetic compressor with a split phase motor. The difference is in how the start winding is taken out of the circuit after the motor starts. But in both cases, the start winding is taken out of the circuit by some type of external switch after the motor starts.
Hi Sean,
One thing I wanted to point out in case you missed it… there are reading assignments in the accompanying reference book. In Unit 3, for example, there are some additional problems assigned on page 98 of the book. Some of the quiz questions are written with the assumption that the student has completed the readings and/or problem solving exercises.
You’re doing great and exactly the right thing: if you’re not sure about something, either in the course material itself or in the accompanying reference book, just ask here like you’ve done and we’re always happy to help. Your training experience here at MST is more than just the online content– it also includes human instructors to help you grasp the concepts you’re struggling with.
Learning electricity is more difficult than learning something like plumbing, for example, because you can’t see it and it is not intuitive like it would be for a mechanical problem. Just stick with it and ask all the questions you need to ask and soon it will click with you. We love seeing when that light bulb go off in people’s heads once it clicks in for them. This will be you soon!
December 5, 2018 at 11:23 am in reply to: Mod 2 Unit 6 Testing inverter Compressor resistance – video #15038Is it possible at all that the problem could still be with the compressor?
It is possible but not probable. These three-phase BLDC compressors are very reliable compared to the split-phase compressors. The reason for this is that BLDC compressors do not have the violent start current inrush that their split-phase cousins have. This is the number one killer of any electric motor. High inrush current causes extreme starting torque (mechanical stress) and heats up the varnish insulation on the motor windings (thermal stress) causing them to breakdown overtime and develop high impedance paths to ground.
We can test split phase motors with a cheater cord. But you can’t do that with a BLDC motor because you need a three phase power supply. So, for all practical purposes, resistance testing is all we can do on the three phase BLDC motors… for now.
Linear compressors, on the other hand, CAN be tested with a cheater cord. There’s only one winding in a linear compressor motor and this can be connected directly to a 120VAC single phase supply to safely test the compressor.
Instead of hopping around to different possibilities and making guesses, let’s stick with the Ten Step Tango process.
1. Problem statement: Motor not running. Thermal fuse keeps blowing.
2. Schematic Review: electronically controlled dryer with standard split phase motor.
3. Load of Interest (LOI): motor
4. LOI circuit analysis: Thermal fuse and belt switch in the Line side of the motor. Line is switched to the motor by a relay on the control board. Motor Neutral side connects to Neutral through the door switch.
5. Troubleshooting hypothesis: An overheat condition is causing the thermal fuse to repeatedly fail open.
Before we go on to step 6, review my previous reply for a summary of common causes for the thermal fuse to open. Looking at the heater circuit on the schematic, you’ll see that L1 is supplied to the heating element from a relay on the main board and goes through a thermal cutoff and hi-limit thermostat.
This model does not have a cycling thermostat and, instead, uses and thermistor to sense and control the heat. So now the question becomes: what does this thermistor do and how does it work. Watch this webinar recording– it explains thermistors and how they work with control boards to regulate temperatures. Whether it’s temperature inside a refrigerator or a dryer, this control scheme (thermistor and control board) works the same way. Watch the webinar recording for a detailed explanation of how these control systems work.
-
AuthorPosts
