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Nuvistor
User Rank
Iron
Self Test
Nuvistor   8/12/2014 1:37:46 PM
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I remember when I used to work on some of the first solid state Whirl Pool and Kitchen Aid washers a long time ago. The control PCB had a two pin connector on it. If you momentarily shorterd the pins together, the machine would go into test mode: First the cold water valve would open for a few seconds and then shut off. The hot water valve would do the same thing. Then it would adjatate for a few seconds and then pause (Neutral drain before spin). Finally, it would spin. This would run the machine through the paces and you could easily see which output did not work. I am not sure if Whirl Pool still does this but it was a very usefull test. If a fill valve fails, it is a good idea to check the inlet screen and hose screen since they are the first to clog before the valve fails.

William K.
User Rank
Platinum
Troubleshooting without the manual
William K.   7/24/2014 4:55:43 PM
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The best way to diagnose a machine failure is by understanding how the machine is supposed to work. So if the problem is that the fill valve is not opening the first step is to check and see if it is being asked to open. Checking voltage across a solonoid valve is not hard, and either the voltage is correct or it is not. If voltage is present and the valve does not open then placing a screwdriver near the coil will tell if it is operational. Voltage present but no magnetism is a symptom of an open coil. An ohmmeter check with the power off verifies the failure as an open coil. And no matter what the manual claims, I would suspect a valve coil before a water level sensor.

wbswenberg
User Rank
Gold
Trouble Shooting
wbswenberg   7/9/2014 6:51:15 PM
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I like to watch the thing work also.  I think about what it does and what it does not do.  The neighbor had a problem with his dryer.  Looking at the block schematic was very cryptic.  I like to jump around the problem depending on normal open vs closed.  We jumped around sensor and the dryer work.  So we knew what the problem was.  He surprised me and found the part and replaced it within a couple of hours.

Same with his furnace.  When we got it to work we knew were the bad part was.  The furnace tech just could not spent time with it.  Good training for me cause then mine failed.  It was a bit faster cause I was familiar with the circuit.  

Larry M
User Rank
Platinum
Re: Another washing machine debug
Larry M   6/25/2014 10:03:36 PM
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timbalionguy wrote: "I have never seen a triac fail like that, but I will certainly remember this one for the future."

Things have changed a little since 1984 when that washer was built. Products like IGBTs are used now, and even SCRs and Triacs are more robust than they used to be, with more isolation trenches, etc., to eliminate the parasitic devices formed when you try to build a PNPN device on a substrate.

I haven't done component reliability work for since 1975, so it wouldn't surprise me to learn that this failure mode really is a thing of the past--like the washing machine.

Larry M
User Rank
Platinum
Re: Another washing machine debug
Larry M   6/25/2014 9:58:54 PM
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Tekochip wrote: "All of the code was designed to pinpoint a failed device or wiring, but the control itself was treated as a black box.  If there was anything wrong on the board it would be replaced as a single component.  I really can't blame the manufacturers for this, because the days of appliance repair technicians coming into your home with a soldering iron and an oscilloscope are long, long gone."

I actually did look for a replacement board. I didn't start this deep level of debugging until I learned that the boards were no longer available. Given that I had had good service from the washer and had just replaced the outer drum, I felt driven to make it work again. Yes, I probably invested 4-5 hours debugging over five days and 10 or 15 minutes effecting the repair, but it was worth it.

I can't see a service guy doing this sort of thing in any of the last four or five decades, but in the 1950s I was very impressed by my Scoutmaster, an IBM CE. He told stories of failures in assemblies where the customer desparately needed the machine and no replacements were locally availalble. He went to a nearby Radio-TV repair shop and got discrete resistors and capacitors to replace the failed unit and got the customer going again. I could do no less.

Did you know that I just retired from IBM after 45 years of service?

timbalionguy
User Rank
Gold
Re: Another washing machine debug
timbalionguy   6/25/2014 9:30:27 PM
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Larry M, that was definitely worth the long read. I have never seen a triac fail like that, but I will certainly remember this one for the future.

My washer and dryer, dating from early 2002, still use mechanical timers, and in the case of the dryer, a simple moisture sensor circuit. They have never given me any problems, and if they do, they are simple to troubleshoot. If I have to replace these appliances someday, I hope the new ones will be as simple.

I occasionally visit a friend of mine in another part of the State to take care of their animals while they travel. They do this frequently enough (plus like to entertain guests) that they built a really nice apartment for me to stay in while visiting. They splurged ina put in state-of-the-art appliances. No more simple wash/dry cycles. these beasts are so complex in what they do that it boggles the imagination. I have atually enjoyed watching them go through the machinations they do to wash and dry clothes (and the dishwasher is even worse!). I will have to say though, they do a superb job.

tekochip
User Rank
Platinum
Re: Another washing machine debug
tekochip   6/24/2014 2:29:45 PM
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I wrote code for a few washing machines, and the ones I was involved with all had detailed specifications for diagnostics that actually took up as much code space as the run time for the machine.  All of the code was designed to pinpoint a failed device or wiring, but the control itself was treated as a black box.  If there was anything wrong on the board it would be replaced as a single component.  I really can't blame the manufacturers for this, because the days of appliance repair technicians coming into your home with a soldering iron and an oscilloscope are long, long gone.


Frogman842
User Rank
Iron
Re: A great story, thanks.
Frogman842   6/24/2014 1:43:19 PM
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@fdos-

Plastic dishes!

a.saji
User Rank
Silver
Re: Another washing machine debug
a.saji   6/23/2014 5:08:01 AM
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@LarryM: Good set of points mate. I think they are only concentrating on replacing rather than repairing because of the cost I guess. 

fdos
User Rank
Iron
Re: A great story, thanks.
fdos   6/23/2014 1:27:34 AM
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@frogman: I need some advice from you on the dishwasher. Im kind of confused on how do they clean each and every dish without damaging it ? According to my knowledge the dishes do need to rotate properly to clean it entirely. So how can this work without clashing with each other. 

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