Whirlpool Duet GEW9250PW0 resurrection

It’s been a while since we’ve fixed anything. But no worries- something always breaks around here!  Lately, our fancy electrical dryer decided to call it quits. 

The symptoms were typical and described all over the net: no response to the power-on button, a few LEDs glowing faintly and interior bulb turning on with the door open. Occasionally, I could also get things to start by flipping the dryer breaker off and letting it sit for a few days. Yeah, very popular with SWMBO. The solutions were all over the place too and mainly suggested replacing either the control board ($250), user interface panel ($145) or a thermal fuse $12). Problem is, you need to know which one you actually need first and that requires debugging.

Taking off the kick panel yielded a baggie with a service manual and schematic in it- very handy. Thermal fuse turned out to be perfectly fine though. Oh well.

So now we are down to the electronics.

Taking the unit apart turned out to be very easy- take three screws out on the back, slide the top cover off, then the control board is on the left, easily accessible.  Looking at the schematic, not much can prevent things from turning on.

Dryer schematic

Dryer schematic

The lamp being on indicates we have 120V present. Checking on the terminals at the control board confirmed that as well. So it is now down to either that board or the user interface one. I removed both (it takes a few screws and disconnecting several connectors) and set them up on the bench to debug. Luckily I’ve been able to make it fail on the bench- very important step in any debug:

All the controls on my bench- much more convenient and no sharp metal around

All the controls on my bench- much more convenient and no sharp metal around

Barely glowing 7 segment

Barely glowing 7 segment

 

Dimly lit LED

Dimly lit LED

The system was still refusing to see any key presses, so I started poking around with a scope. The whole thing runs off a single Freescale micro co-branded with Whirpool and in a giant DIP package. 5V supply and reset looked fine and there was definitely activity on the IO- I could see the micro scanning keypad lines.

Scan signals

Scan signals

Looking at the number of LEDs and buttons it soon became clear that some major multiplexing was used. There was just not enough signals coming over the 14 and 6 pin cables between the boards to drive everything directly. They did though have three dedicated inputs that were going to special function buttons- things like Power On, Start etc. And two of these had a differing waveform than the third. (which happened to be a Power On!). Ok, getting somewhere.

So I kept poking and prodding and could not see any obviously faulty components.I replaced cable between the boards with separate wires and tried removing them one at a time to see if the problem persists.  I even went ahead and resoldered all connectors between the two boards but nothing changed.  As I sat there staring at things and trying to sketch how the whole mess of a multiplexing was implemented, I accidentally bumped one of the LEDs  ( I think it was D15, Wrinkle Guard) and noticed the dimly lit other ones flickered.

The culprit

The culprit

I prodded it again and the lights went off, but the system started. And of course the scan signal on the PowerOn button now matched the other two. Interesting! So I powered off the boards and resoldered all LEDs on the whole front interface assembly.

Main UI board

Main UI board

 

Smaller UI board

Smaller UI board

Power cycled and things were up and running. I ran built in diagnostics and all LEDS lit up normally:

Running diag

Running diag

Conclusion:

It’s now been a few months since the repair and the dryer still starts every time. I’ve been too lazy to trace out what exactly the designers multiplexed together but it appears they used reverse biased LEDs as diodes in the scanning matrix. As a results LEDs that are off still affect things and all it takes is one bad solder joint in one distant corner of the board to make a seemingly unrelated PowerOn button stop working.

Disclaimer:

If you try this on your own, make sure you know what you are doing, always disconnect power and proceed on your own risk. High voltages are present in the dryer!

 

 

 

 

 

7 thoughts on “Whirlpool Duet GEW9250PW0 resurrection

  1. Great write up. I had the same symptoms and re-soldered all the front user interface LEDs as you suggested. Everything is now back to normal. Thanks.

  2. Well the things you find when you are looking for something else. I just happen to have the same units and have had to replace the main control board, (it hurt the wallet) as the build up of dust in the dryer case was too much for the electronics. It is very advisable that if you have one of these dryers that you pull the top cover at least once a year (depending on your use) and clean out the dust. JUST MAKE SURE THAT YOU UNPLUG THE DRYER FIRST. Thanks much for the write up and pics.

  3. Thanks for the info. We noticed on ours that one of the LED lights is not working at all. Any idea where to start to replace the LED?

    • Same deal- take the display board out and touch up solder points for the LED in question and anything that looks questionable

  4. Yours is the most useful info I’ve found but still no joy. I’ve been fighting this same issue for a few weeks. Re-soldering just the LEDs and even replacing all the switches did not solve the problem. I’ve now re-soldered every connection and via on both control panel boards and it’s working again. But, just as you said, even unplugging it for a few hours or overnight can make it work again. So sometimes “fixed” is just getting briefly lucky and then it’s dead again.

    It’s a very odd problem in that letting it sit without power often temporarily lets it work. But it has to be at least a few hours and sometimes overnight. Unplugging it for even 30 minutes doesn’t work.

    I’ve tried freeze spray to cool both boards, and tried heating them as well, and didn’t get any consistently different results. Normally a bad solder connection, or PCB trace/via, will get worse or better with cold and/or heat.

    There’s nothing on the control panel boards that makes any heat. And just leaving the dryer plugged in and not having run (hence no heat) since the day before will cause the symptom. In my case the high-temp LED glows dimly when it’s “glitched” and the control panel will be entirely unresponsive. How does leaving it unplugged fix it under those conditions?

    Looking at signals at the switches with a scope there’s some extra noise on two of the three switch polling signals when it’s unresponsive and they’re not pulling down as far. But the signal is still there, still looks valid, the timing is the same, etc. It appears the microcontroller is trying to do its job but getting the wrong data back.

    You’re correct about the design being heavily multiplexed. I think the engineer responsible got a bit carried away to save a few wires as the result is like a string of Christmas lights. One bad bulb can render the entire string–or in this case dryer–useless. It’s a very fragile design especially when their own control panel diagnostics cannot even be run when the entire panel is unresponsive and you can’t enable the diagnostic mode.

    The front panel assembly is currently around $300 and the control board with the power supply and microcontroller, which could also be the problem, is another $300. Electrical appliance parts are non-returnable if they’ve been installed. So I’m reluctant to spend $300 – $600 when I can buy a similar working entire dryer on Craiglist for $150 or a new comparable GE dryer for $650.

    I get that manufactures want a healthy profit on replacement parts. And they don’t want to provide complete schematics so their boards might actually be repaired. But, by making those choices, they’re also filling up our landfills with otherwise working appliances that just need one part but are not cost effective to repair. They’re also driving people to try a different brand next time.

    Whoever designed the thing thought they were being clever saving $0.10 worth of wire and ended up with a very fragile design that causes the entire dryer to fail if nearly anything goes wrong on the complex front panel assembly. Between the poor design, lack of detailed service info, and high cost of parts, I’m done with Whirlpool.

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