May 14, 2014
In this journey into Total Appliance Enlightenment, Samurai Appliance Repair Man shows you how to troubleshoot a problem with a newer Whirlpool front load, direct drive washer (one of the new Alpha2 platform washers) that acts like it wants to start but won't. This one had a couple of curve balls:
- It wouldn't even run any tests in diagnostic mode because the CCU (central control unit-- main microprocessor control board) won't run those tests if it thinks the door is open. So although I could enter diagnostic mode, I couldn't get the machine to to anything.
- There were no error codes either in normal standby mode or in diagnostic mode.
- The problem was intermittent (which I didn't show in the video for the sake of brevity and clarity). On the first trip out there for the same complaint (no start) I pulled the DCS3 connector off the CCU and tested the door switch and it tested fine. How did I know to do that? I explain that in the video. Anyway, the washer ran fine upon reconnecting the DCS3 harness. I figured it was a bad wire harness connection so I tightened up the tines in the harness connector, double checked proper operation and left. A week later, I got a call back for the same problem, no start.
Watch with shock and awe as I ruthlessly hunt down the miscreant part and guide you through the troubleshooting process both on the machine itself and on the schematic diagram, demonstrating killa troubleshooting techniques that every tech should know.
Okay, that's the solution to one scenario that could be preventing the washer motor from running. But what if you check that door switch and it's good? What else could be the problem? Excellent question, my fine, young apprentice! Let's look at that:
Building top-notch troubleshooting skills, reading schematics, and understanding the technology used in today's appliances are core teaching points in the Academy course, Fundamentals of Appliance Repair. All graduates of the Fundamentals course are well-versed in these skills.
And here's the Tech Bundle Care Package for these new Whirlpool Alpha2 front load washers that I promised you in the video. You'll need to register here at the Academy if you are one of the remaining few who haven't already (it's free!) and be logged in to download it.
Thanks, Sensei!
After checking the 3 windings, do you check if they are grounded to the motor? Or do you only check for a grounded winding when they should read differently?
Ahh, my fine, young Apprentice! You have have snatched the pebbles from my hand! Yes, checking for a grounded winding would be a reasonable and expeditious test to make while checking the motor winding resistance. I wish I had mentioned that in the presentation.
Let it be known to all present that Allen is a Boot Camp graduate with Highest Distinction who pointed this out. Kudos, Allen!
How do you tell what part is AC and what part is DC on a schematic?
Great question, Roger! We determine this by doing what we learned in the Fundamentals course as a “Load Analysis.” That is, we review the schematic diagram, focusing on the load in question, and determine how that load is supplied with power.
AC loads will trace out to Line and Neutral or L1 and L2.
DC loads will trace out to a voltage called out as + (some voltage) and then to a DC common.
Remember: AC ground is not DC ground. Two separate ground/common systems. You can think of AC and DC as existing on parallel universes. Both doing important and tangible things in the here and now but must never cross paths with each other.
Re:ac/dc separation
It is always a good idea to separate the two, but not every brand does that.
Amidst my absinthe-minded fumbling around, I tumbled upon such a case of negligent design some time ago. I went to perform a dishonorable gig of rectifying someone else’s botched repair job. He was an automobile mechanic who decided to tackle a squeaking drum bearing. When taking the unit apart he failed to take notes or photos to later see what goes where. He mismatched wires to the heating element and temperature sensor.
Bad design part one – both devices were near each other, which is obvious, but connected with similar gauge wire and the same size of connectors. Two grey and two white wires. The mismatch caused the 5V regulator on the MCU to blow. I managed to get the unit going by replacing the regulator and correcting the heater wiring.
Bad design part two – as we are in Yurup and most single-phase appliances can be plugged with either polarity, and are mostly designed to work either way, this one made no difference. But the MCU was the first part of the power chain, with wires from the plug coming into it, and making DC for the unit. Pulsed DC to be clipped by thyristors for the motor, and steady 5V DC for the logic circuitry. Only this was made so that the 5V rectifier used the same common rail on the board as the rest of the unit. This leads to an intriguing situation where the orientation of the power plug makes it possible to have (or not to have) 230V AC coming all the way up to the control panel. The 5V DC will then ride as an offset on top of the 230V line. Whether or not the logic circuitry can work that way is not really important. But there may or may not be line voltage present at the end of the thin ribbon cable of the control panel where the unwary may not be expecting it.
I’m telling this as a warning because even though most US devices are polarised, it is possible to have a miswired socket. With a machine of such design I described, you may unknowingly have mains power present at a logical common rail.
Howdy, Keino, and thanks for sharing your enriching story. Yes, I have seen DC and AC sharing a common in other equipment but never in home appliances sold and used in the US.
All home appliances sold and used in the US observe strict separation between AC and DC. Even Samsung and LG. Or maybe I should say *especially* Samsung and LG because they both are electronics companies with a lot of experience using electronic controls in appliances and know the importance of maintaining separation between AC an DC.
In fact, you’ll find the manufacturers taking extra efforts to maintain that separation between AC and DC. For example, in addition to using two different ground systems, they will even add noise filters to prevent electromagnetic interference (EMI) generated by the AC from affecting the DC electronics.
But y’all do some strange things over in Europe– heck, even your AC runs at a different frequency. 😉
But here in the US, separation between AC and DC circuits in appliances is dogma and I reiterate my sweeping statement that AC ground is not DC ground. This is an important troubleshooting concept for American techs to grasp because it affects things like how voltage test measurements are made, for example.
A common mistake for an uninformed tech is to measure a DC voltage at a test point on a control board but have the other lead of his meter clipped to chassis ground. This will give false readings, leading to false conclusions (the most common one being that the board must be bad when it really isn’t).
As far as appliantologists in the US are concerned, AC and DC exist on parallel universes and never cross paths with each other. American techs need to keep this in the forefront of their minds when troubleshooting home appliances.
This was a cheap unit made in the former eastern bloc, past the 5 years life expectancy and I wonder why he bothered attempting repair at all. But then, what the heck. He paid and the job was no big deal.
The data input to the MCU is unlike the input for a GE compressor inverter board since you can actually measure the input to the compressor inverter board (0-5v depending on desired speed), correct? I’m lost as to why you can’t measure the data input for the MCU – is it not a PWM signal?
How can you conclude that the CCU is sending a signal via the data line if it cannot be measured with a simple multimeter? I would be running a full diagnostic to test all other functions of the washer to help rule out the CCU.
Is there a portable meter that can measure this data line?
H Michael,
Variable frequency drive systems, such as used in this washer, are also used in many other appliance applications, inverter compressors being just one of them.
I do say clearly in the first video that this is a variable frequency drive system and the MCU is getting a Pulse Width Modulated signal from the CCU.
Let me answer some of your other questions with a thought question for you: What IS a pulse width modulated signal?
We discuss how to use your DMM to check a PWM data line in Episode 6 of our podcast: http://mstradio.com
In the video, I also say that we go into great detail about variable frequency drives and PWM communications in the Motors module of the Fundamentals course. I explain what the PWM signal is, what it means, show what it looks like, and how to troubleshoot them: http://mastersamuraitech.com/appliance-repair-courses/fundamentals-training/
In the Advanced Schematics and Troubleshooting course, I go into great detail explaining how other control board systems used in appliances communicate with other and how to troubleshoot them: http://mastersamuraitech.com/appliance-repair-courses/advanced-schematic-analysis-and-troubleshooting-course/
I guarantee you would benefit from both!