HOME  |  NEWS  |  BLOGS  |  MESSAGES  |  FEATURES  |  VIDEOS  |  WEBINARS  |  INDUSTRIES  |  FOCUS ON FUNDAMENTALS
  |  REGISTER  |  LOGIN  |  HELP
Page 1/3  >  >>
wbswenberg
User Rank
Gold
Trouble Shooting
wbswenberg   7/9/2014 6:51:15 PM
NO RATINGS
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
NO RATINGS
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
NO RATINGS
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
NO RATINGS
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
NO RATINGS
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
NO RATINGS
@fdos-

Plastic dishes!

a.saji
User Rank
Silver
Re: Another washing machine debug
a.saji   6/23/2014 5:08:01 AM
NO RATINGS
@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
NO RATINGS
@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. 

Larry M
User Rank
Platinum
Another washing machine debug
Larry M   6/22/2014 8:49:13 PM
NO RATINGS
(This should really be a Sherlock Ohms submission.)

I'm still using the washing machine my late wife and I bought in 1984. It was one of the first ones with solid-state control. We selected it because we were tired of repeated failures with mechanical timers. Either the motor or contacts would fail and replacements were outrageously expensive. (GE/Hotpoint had come up with a timer with replaceable contact points by then, but the timer motor was still a weak link.)

The first problem with the washer, a Whirlpool, occured in 2007. The outer tub rusted through near the outlet and had to be replaced. After I did so, the machine failed to operate properly. It would start, fill, and then agitate continuously, never proceeding to a spin (and pump), fill, rinse, and subsequent cycles.

The electronic control was straightforward with pin-through-hole construction. It had what looked like an 8041 microcontroller with sensor inputs (door, water level sensor NO and NC contacts) and outputs which drove the machine (motor on/off, two solenoids on the transmission) through simple diac/triac circuits. All the components and circuits were clearly silk-screened on the board and Whirlpool had helpfully provided an inserted pamphlet with a block diagram.

I first discovered that I could turn the washer off, and then start it in the spin cycle and it would properly empty the machine of water. I also discovered that if I let the machine fill and agitate beyond the expected time and then removed the pressure hose from the water level sensor, that the machine would continue on to spin, the next cycle portion.

Consultation with the experts on the forums gave only the following unhelpful information:
  • It could be either the water level sensor ($50 or so) or the controller board ($350)
  • Both components were no longer available

so I knew I would have to figure it out myself.

Now the problem with debugging with an electronic timer rather than a manual one is that the only way to advance the timer is to wait for it--there's no knob to rotate. So after some head-scratching I decided to follow the awful and hard-to-read timing chart on the back of the washing machine.

I chose to trace the Gentle cycle because the wash cycle was only eight minutes; the other two were twelve and fourteen minutes. It was fortuitous that I did so.

Crouching behind the washing machine studying the timing chart and watching the works as it filled, then the water level sensor caused the microcontroller to start the agitator as the motor ran at the slower, gentle speed. After eight minutes the motor suddenly advanced to the faster speed as agitation continued. This told me that the microcontroller was working. After thinking about it for a bit, I disconnected the water level sensor hose and the drum began to spin as water was pumped out. But the timing chart said the water was to be pumped out and then spin would begin.

Time for more thinking. The transmission has two solenoids. That means it has three or four states. The identified states are:
  1. Agitate (no pump, no spin)
  2. Pump
  3. Spin and pump

The state was never changing from Agitate to Pump. Watching the solenoids as I went through the sequences of Off-->Spin and the long Off-->fill-->Agitate-->Pump let me identify that the Agitate solenoid wasn't releasing at the end of the wash portion of the cycle. I poked at it and determined that it was still energized. When turned off, it moved freely so it wasn't mechanically stuck. And now the problem became very simple.

Early in my career I had worked for a few years in reliability physics and one of the components I had evaluated was SCRs. Triacs are similar to SCRs. One of their well-known failure modes is latch-up. When an SCR or Triac suffered this failure it would remain off when biased (as it should), and turn on when triggered (as it should), but it would not turn off at the next zero-crossing when the trigger was removed (as it was supposed to).

And this was exactly what was happening. The triac turned on for the agitation and wouldn't turn off to shift the transmission so the pump would run. The microcontroller was waiting (forever) for the non-running pump to drain the tub. If I removed the sensor hose, the controller would start the pump running and spin while there was still water in the tub, instead of pumping without spinning until the tub was empty, then spinning. If I turned the machine completely off and then started it directly in the spin cycle, the Agitate triac was never triggered so the pump worked fine.

Of course the original triac part number was nowhere to be had, but I was able to order a triac with the same case and pinout from Mouser Electronics. They had units rated at 110v for 35 cents, 220v for 36 cents, and 440v for 37 cents. I thought the higher breakdown voltage might reflect a more reliable part so I splurged on the expensive one. 

It took just a few minutes to unsolder the defective triac and install the new one and the washer has worked fine ever since. I did let the forum experts know that the washer had been fixed for 37 cents, but never received a response. I guess they were more expert at replacing modules than working at the component level.

Frogman842
User Rank
Iron
Re: A great story, thanks.
Frogman842   6/18/2014 3:02:18 PM
NO RATINGS
My Fisher and Paykel washer, dryer and dishwasher have excellent troubleshooting guides and modes. 

You can exercise all the valves, lights and motors, test the switches and read the sensors. All from the front panel display.

My wife's washer had a problem that was easy to diagnose - AND REPAIR. The offending sump pump had a decent connector for the motor and the assembly twisted out by hand with a coarse threaded fitting. And the part was not expensive or hard to find.

Well done. They have me as a customer for life.

David

Page 1/3  >  >>


Partner Zone
Latest Analysis
This Gadget Freak review looks at a cooler that is essentially a party on wheels with a built-in blender, Bluetooth speaker, and USB charger. We also look at a sustainable, rotating wireless smartphone charger.
Texas Instruments is rolling out a new microcontroller that could make the design of sensor networks and data logging systems simpler and less costly.
Made By Monkeys highlights products that somehow slipped by the QC cops.
From pitchers and forwards to quarterbacks and defensemen, we offer a peek at some of the more memorable engineers in sports history.
IBM announced it is dedicating $3 billion of funding over the next five years to research and development of new processor technologies.
More:Blogs|News
Design News Webinar Series
7/23/2014 11:00 a.m. California / 2:00 p.m. New York
7/17/2014 11:00 a.m. California / 2:00 p.m. New York
6/25/2014 11:00 a.m. California / 2:00 p.m. New York
5/13/2014 10:00 a.m. California / 1:00 p.m. New York / 6:00 p.m. London
Quick Poll
The Continuing Education Center offers engineers an entirely new way to get the education they need to formulate next-generation solutions.
Jul 21 - 25, Design Products With Bluetooth Low Energy
SEMESTERS: 1  |  2  |  3  |  4  |  5  |  6


Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.
Next Class: August 12 - 14
Sponsored by igus
Learn More   |   Login   |   Archived Classes
Twitter Feed
Design News Twitter Feed
Like Us on Facebook

Sponsored Content

Technology Marketplace

Copyright © 2014 UBM Canon, A UBM company, All rights reserved. Privacy Policy | Terms of Service