My $2.87 Kenmore 90 Plus Series "Evenheat" Repair - Board 3402605

[CorinthWestMissileBase]

Model Number: 110.68932790

Brand: Sears Kenmore

BACKGROUND: Last Thursday, my lovely wife informed me that our Sears Kenmore 90 Plus Series electric dryer with "EVENHEAT" had stopped working. She described the issue as "the dryer would start when the PTS button was pressed, but would shut off as soon as the button was released". The dryer is going on 12 years old. I asked my lovely wife to unload the dryer and put the clothes out on the line to dry. I then proceeded to start my diagnostic tests.

STEP 1: Since the dryer would run with the PTS button depressed, I knew the problem was not external to the machine (IE. a breaker or outlet issue), nor was it a PTS switch issue or a motor issue. I unplugged the dryer and opened the console cover. The machine has a control board manufactured by FSP and a part number of 3402605 (this is important in that I don't know if these tests and subsequent repairs would be applicable to another board, like the modified replacement board that is now sold for this unit that uses 48V DC relays instead of the 120V AC relays used in this original design).

STEP 2: Not knowing if this was a relay issue, or a control board issue, I elected to test the motor relay first. This is one of the relays under the console cover with multiple wires going to it, of which 2 (identically marked) are PINK with a BLACK stripe. These 2 wires control the primary coil of the motor relay. One of the PINK/BLACK stripe wires goes to the control board. The other is a 110V AC hot feed. The control board grounds the other PINK/BLACK stripe wire, thus closing the relay and keeps the motor running when it senses the PTS button has been depressed. I disconnected the PINK/BLACK stripe wire connecting the control board to the relay at the relay. I took a jumper wire and attached it to the now exposed primary terminal on the motor relay. I then plugged the dryer back in. With the dryer plugged in, I proceeded to ground the other end of the jumper wire to the dryer frame (ground), thus energizing the relay. The dryer started running. Therefore, I knew the relay had supply voltage and was indeed good.

STEP 3: Having eliminated external power issues, the PTS button, the motor and the motor relay, I now turned my attention to the control board. With the dryer still plugged in, I placed a neon test light across pin # 1 on connector PS01 (top left connector, bottom pin) and pin # 1 on connector PS02 (bottom right connector, top pin). These are the pins that supply the 110V AC supply voltage to the control board. I read 110V AC (the neon light lit up) across these pins, and therefore I knew the board had power.

STEP 4: Now that I knew the control board had power, I needed to know if the board itself was dead or alive. I proceeded to attempt to put the control board into "Factory Test" mode by opening the door, setting the SELECTOR to "TIMED DRY", setting the FABRIC TEMPERATURE to "AIR FLUFF", setting the SIGNAL to "LOUD" and turning the WRINKLE GUARD switch from "OFF" to "ON" and back 3 times within 5 seconds (see the "Tech Data Sheet" found under the console cover for more information on these tests). This "should" have put the board into diagnostic mode as indicated by a loud beep. No joy. The board was dead.........much to my dismay.

Note 1: In retrospect, this will be the FIRST test I perform should I have problems with the machine in the future - very simple to do and can be done without so much as opening the console or removing a single screw.

Note 2: Up to this point, the only tools I have used to make the determination that the control board was bad are a phillips screwdriver to open the console, a jumper wire to test the motor relay, and a 110V AC neon test light to check the supply voltage to the control board. In total, less than $5.00 in tools, all of which I already had in my tool box.

STEP 5: Now that I knew the board was the problem, I unplugged the dryer and removed the board. In looking at the board, I saw nothing out of the ordinary. No burn marks, no blown caps, no fried resistors, unlike many other posts I have read out here on this site. The board almost looked new. This is where things get interesting.......Upon further examination, I saw that there are a total of 7 diodes on the board (3 black epoxy and 4 glass germanium). I started looking for a bridge rectifier configuration because I suspected it was a power supply problem on the board and it is common for a bridge rectifier diode to fail which would cause this type of problem. I couldn't find a bridge rectifier configuration, but decided to check the diodes anyway. I desoldered 6 of the diodes from the board and tested them. All 3 of the black epoxy diodes tested good (D01, D10 and D14). I was able to check another germanium diode on the board (didn't require removal), and it was also good (D08). However, the last 3 diodes I checked were all bad (D02, D05 and D09). I looked at the numbers on these diodes and they were all 4745AP, which are 16V Zener diodes. Looking closer, I noticed these Zener diodes were placed in series on the board, which would provide 48V DC to the down leg circuits. If these diodes were open (and they were), this would account for the lack of supply power to the rest of the board, including the PROM, and could potentially be the reason why the board appeared "dead". I crossed the numbers over to Motorola and found that the replacement diodes were 1N4745A. I checked Radio Shack and the closest thing they had was 1N4742A, which are 12V Zener diodes, and these would not work since 3 of these placed in series would only provide 36V DC, and the board was designed for 48V DC. I therefore called my local electronic supply house and ordered the 1N4745A diodes. They arrived on Monday and I picked them up and installed them on the board, taking care to reorient them exactly the way they were originally placed in the circuit. The electronic supply house charged me $.90 for each of the 3 diodes (plus tax) for a total of $2.87.

Note 3: This design (using Zener diodes to provide regulated DC voltage instead of a step down transformer, bridge rectifier and voltage regulator) epitomizes the "cost wins over quality" in today's disposable society where engineering requirements include specifications for "Preplanned Obsolesence". This is a pizz poor design in my opinion, where the customer got an inferior product so that the manufacturer could make a few extra dollars. What makes me angry is that they STILL charge $150+ for this (POS) board, that cost them about $5 to $10 to make.

Note 4: Before attempting to fix the control board, I called Kenmore and requested a "free" replacement board since I saw there was a Service Flash on this problem (found through this blog - thank you), and they gave me the standard song and dance about sending a technician out to look at the problem and replace the board (all at my expense). I laughed at them and said that they clearly knew they had a problem because they had issued the Service Flash indicating replacement of the board, and that the replacement board had been redesigned. They apologized and said there was nothing they could do. Bottom line was, I absolutely REFUSED to spend $150+ to purchase another poorly designed replacement board.

Note 5: I think I "could" have used 4 1N4742A Zener diodes in series (obtained from Radio Shack) in place of the 3 1N4745A Zener diodes to obtain the 48V DC. But this would have been messy in my opinion since there is only space on the board for the 3 original diodes, and the fourth would have had to be installed in series on the top side of the board. This would have violated my personal prime directive of fixing things such that when finished, they don't look like they have been repaired. The correct diodes were easy enough to obtain. Had they been difficult to get, I might have gone with the 4 Radio Shack Zener diodes.

STEP 6: I reinstalled the repaired board and put the PINK/BLACK stripe wire back on the primary connector on the motor control relay. I then plugged the dryer in and proceeded to put the control board into "Factory Test" mode......"BEEP" - "IT'S ALIVE!!!!" I exclaimed loudly. I then proceeded to run the diagnostic tests and EVERYTHING WORKED! All switches and sensors passed the tests. I then buttoned up the console, wiped it all down with Windex and turned the dryer back over to my lovely wife. She made me a yummy chocolate cake to thank me later that day and I am eating it now as I write this - "ummm....c-h-o-c-o-l-a-t-e" (in my best Homer Simpson impression).

CONCLUSION: I was lucky, and I knew it. That's why I exclaimd "IT'S ALIVE" when the control board went into Field Technician Diagnostic Mode ("TEST" mode) after the repair - *I* was surprised it worked. Had the Zener diodes SHORTED instead of OPENING UP, the resulting high voltage most likely would have damaged components on the down leg side of the board (including, but not limited to the PROM). But because the Zener diodes had OPENED UP, the rest of the board was spared any consequential damage. Therefore, I see no reason why I shouldn't expect to get another 12 years out of this control board (until the Zener diodes fail again). Only time will tell..............$2.97 well spent, and less time to diagnose and fix than it took me to write this post. I sincerely hope this post helps some other poor b$#tard out there with the same problem - smiles.

[jmshaffer]

Haha, you're very intuitive. Unfortunately, the appliance repair industry doesn't do component replacements any longer. The days of using ocilloscopes are all but over. Good to see you gave it a good attempt and succeeded. When I was a young technician, I used to do the same thing.

[CorinthWestMissileBase]

Justin,
I don't know about the "intuitive" part - smiles - just persistant and stubborn (spelled C-H-E-A-P), perhaps. My brother has an appliance repair business in the Philadelphia area and is very good at what he does (they keep him VERY busy). When I spoke with him, his comment was "just stick a board in it and be done with it". Obviously, I didn't listen to his advice. However, I understand that if this were a "customer's machine", there is no way I would have done this repair on it, and for a few VERY good reasons - first and foremost is liability (as my brother pointed out to me). Also, the time spent to diagnose and repair the board "could" have been wasted if the repair was not successful, if other components needed to be replaced subsequent to the Zener replacements, or if the board turned out to be completely unrepairable IE. the PROM was fried. This would have resulted in the technician giving his time away, or working with no guarantee of success, and you can't run a business like this - at least you can't expect to make money at it. Bottom line is that while component level repair may be great for the DIY'er, it is not a cost effective way to repair appliances en mass. Replacing the board with a new/known good board (that had a GUARANTEE) MAY have been faster and perhaps more cost effective in the long run. I simply got lucky on this one, and thought I would share my experience with others that may have the same issue and would like to try and repair the board themselves before spending the $150 on a new board (which STILL grates me, if you can't tell).

As a side note, it's interesting that you understood the concept of "component level repair". Most "technicians" that have come into the electronics field in the last 20 years (including appliance repair since so many appliances now use "electronic components"), have absolutely no concept of that phrase. Their idea of "component level repair" means swapping a board. I guess I'm showing my age. And yes, I still have my Tektronix dual trace.........and know how to use it.

P.S. My brother advised me 12 years ago not to purchase this washer and dryer BECAUSE they contained logic boards. The washer and dryer I replaced did not, and were very simple (and inexpensive) to repair. I should have listened to him in retrospect......his comment to replace the board came with some measure of cynicism (smiles).

[jmshaffer]

Hey, I just noticed I misspelled oscilloscope. LOL

I used to help people out with component level repairs back in the day. You are 100% correct that liability is the main concern. I'll tell you, since these appliances have all this technology, there are sooo many things they can do. One of the best tools in my bag anymore is a receptacle tester. You would not believe how many customers of mine are destroying their boards because of faulty polarity or no grounds. Can't get away with that crap with these DC circuits. All in all, I'm happy with the direction the appliance industry is going. The manufacturers are all competing hard for the next best thing and it keeps me bitching, er...on my toes.

I can honestly say, I don't have too many boring days. The hardest thing about my job though is the customer. People are spoiled and don't read their warranties and expect free education calls. They don't read how to use their appliance or their afraid to make adjustments other than what's considered "default settings". I could sit here and gripe all day. Glad to see you're a good ole do-it-yourselfer. Congrats and good reading of your success. I hope you come back with another good story for us.

[GIV Tech]

Corinth,
I must say, great minds think alike, I had done everything you did exactly, but when I came to the conclusion that the board was dead, I was ready to throw in the towel and spend the $150 to order a new board. I googled the part number of the board and that is where I came across your post. I have to give you props for your knowledge and understanding of the PC board. I pulled the board and tested the diodes and found they were all three bad as well. I ordered new diodes from Newark.com for $.10 a piece. Once I changed them out, I went straight to the factory test and was thrilled to hear the "it's alive" beep! This had to be the cheapest fix I have done! Thanks for your input it saved me alot of money and I learned something new!

[Earplugguy]

This WORKS!!!!! I paid 0.11 for diodes from Newark.com I paid shipping, but for under $20 I got this repair done. FREAKIN awesome!!!! Thanks, very nicely done!!!!

peace
don

[RES]

Thank you CorinthWestMissileBase for your post! As you can see, you have definitely helped others get going! You can add me to that list. $150 board fixed for $3.99! Huzzah! Huzzah!

I think that it is sub-optimal to replace the diodes with the original part number. At this point, it is pretty obvious that the original zeners are failing, almost certainly because they are running too hot. Four 12V diodes give you the same voltage as three 16V ones, and are much more common. But more importantly, with four diodes you reduce the power that each zener dissipates by 25%, which is likely to lessen the repeat failure rate.

So thanks to CorinthWestMissileBase for finding the problem and starting this thread, to the appliance blog for publishing it, and to Google for enabling me to find it. This internet thingy is getting to be down right helpful to folks like me! Thanks everybody!

[CorinthWestMissileBase]

RES,
I check in every once in awhile to see if this has helped anyone else. I am so glad to see that it has. I'd also like to add that your comments about the Zeners are absolutely spot on. If I ever do this again, I might use 4 x 12V's instead, because I suspect you are absolutely correct in that they are failing due to heat (as usual). 4 Zeners would run cooler by about 8% each. Really good idea. I'm just one of those people that like things to be the way they were "originally". But in this case, if I ever have to do it again, I will probably make an exception.

Thanks for the insight, and pointing out a solution to help dissapate the heat. Kudos.

Now, If we were REALLY clever, we'd redesign the board to use a bloody TRANSFORMER, as the engineers SHOULD have done - LOL.

Good luck everyone.

[RES]

I'm not quite sure how dropping power dissipation 25% drops the temperature 8%, but I'll take it on faith. Actually, I wanted to use eight 6V zeners, which would drop dissipation in each device by 87% mostly because that provides the most stable voltage regulation. (The silicon zener having a zero temperature coefficient is 5.5V) I just went with 12V cuz that's what I could get quick and cheap from ebay. (50 for $3.99 post paid, no tax) If you want to spend even less, I'll mail you 6 of them for a buck. (Murphy says send 4 and one will be bad; send 2 extras and all six will be good!) Eee mail me at myspamaddy1 at gmail dot com with your snail mail addy and I'll send 'em. I'll trust you to mail me a buck for postage and envelope.

American mass manufacture makes me think of the French. They wanted to be less dependent on Middle East crazies, so they went big time nuclewar And get 88% of their electricity that way today. They picked a certain plant size and design, and built them all identical, just like Sears built these dryers. So, if one fails somewhere, you know right where to be looking for a failure in all the others. Often, to upgrade against failure is as cheap as it was here for us. Huzzah! Huzzah!

[jazzye2]

Thank YOU!!!!!! I had the same issue with my Kenmore Dryer. My board had 5 (1N5923) diodes that are rated at 5.2 volts and they were in series for a total voltage of 50. I went to Radio Shack and purchased a 50V diode. Had some fun and replaced the 5 diodes with the one and sure enough my dryer is ALIVE! Below is a picture of the board and bad diodes. I saved over $150 and had my dryer fixed in 2 days.

Kenmore Elite Dryer info - Mod: 110.63942101 , Ser: mp0332569