Kenmore washer 970 controller/display board fried? - Page 1
Forum section: electronics / beginners

author: edy
author_rank: Super Contributor
timestamp: August 04, 2014, 04:56:25 am
content: Hello folks,I have a Kenmore washer model 970-C47092-10 (see attached photos). I went away on vacation for 1 week and returned home to see the unit display panel turning on a few seconds, showing normal, then showing a backwards letter L (on the 3-digit x 7-segment green numeric display), then shutting off, then on again normal, then backwards L or backwards C, shutting off again, and repeating.Normally the unit is off until you turn the front knob to select a wash mode. As you rotate the knob, the display turns on and LEDs change on the different stages of the wash cycle settings to show you the settings for that mode. As well, the numeric display usually will indicate time for that setting. The start button LED usually just flashes until you press it.So now, the display runs through this strange sequence. I can't figure out what it could be. I've tried looking for some service manuals but there are so many and it is hard tracking down this particular model. My next step would be to remove the control/display board and see if there are any obvious component failures. If it is the micro then I'm screwed. Otherwise, maybe a chance I can track it to a simple obvious component. Any experience in this area or knowledge of whether there is a common issue on Kenmore boards would be appreciated. I'll post more pictures and updates here. Thanks!

author: edy
author_rank: Super Contributor
timestamp: August 04, 2014, 04:59:55 am
content: Here is what the display looks like after several more seconds, then it powers off completely, then starts back up normal again.... And repeats indefinitely.....

author: edy
author_rank: Super Contributor
timestamp: August 04, 2014, 05:06:13 am
content: Sometimes it looks like this... And the backwards L or smaller L-like symbol can appear at any of the 3 positions... May depend on how the cycle knob is rotated. Almost as if the micro gets powered up... Then the voltage falls and eventually drops below operational, then somehow gets up to normal again and continues... Or perhaps goes high and some safety mechanism shuts it down, then is able to turn on again, with cycle repeating.

author: IanB
author_rank: Super Contributor
timestamp: August 04, 2014, 05:09:59 am
content: Were there any storms while you were away?A possible scenario is the electronics got fried by a power surge.

author: edy
author_rank: Super Contributor
timestamp: August 04, 2014, 02:14:06 pm
content: I've managed to open up the washer and remove the control board. It looks like the control panel had detergent seeping into the side next to the rotary select knob, probably due to splashing of water into the detergent basin which wet the control panel housing. No rubber seal or gasket or tongue-in-groove assembly... Shoddy engineering! I will post more photos in next reply since I am limited to 2 mb.

author: edy
author_rank: Super Contributor
timestamp: August 04, 2014, 02:18:49 pm
content: Have a close look... you can see a white scum which I assume is detergent. But there are small black shorts or dendritic patterns jumping across via (ground plane?) on quite a few areas on what looks like the higher voltage side of the board. That is the side with the rotary knob and relays and large caps. The side of the board with LED and micros is unscathed.

author: edy
author_rank: Super Contributor
timestamp: August 04, 2014, 02:48:57 pm
content: I cleaned up all that crap with 99% isopropanol and I am very surprised but it actually works again!!!!I failed to mention that prior to disassembly, it stopped working completely (board would not power up when washer plugged in, but would flash the LEDs briefly when I would unplug it). So I am amazed it now works!Could be those little black dendritic spark jumps were enough to screw up current flow? And a bit of alcohol cleanup is all it took?By the way you can see how the soap can get into the high power side of the control board in the photo.

author: corrado33
author_rank: Frequent Contributor
timestamp: August 04, 2014, 02:53:38 pm
content: I'd test continuity between some of the "shorted" pads. Then I'd clean everything with some electronics cleaner and a mild scrub brush or rag and try it again. You may get lucky and have nothing that actually broke. The fact that it comes on, even briefly, is a good thing.I recently fixed my mom's dryer by resoldering a heavy motor control trace on the PCB after it broke open. (Don't ask me how hard it is to solder something with a freaking iron that was used for wood burning and 10+ year old solder...) I cleaned out a bunch of lint that had built up under the drum and it's been working find ever since.

author: edy
author_rank: Super Contributor
timestamp: August 04, 2014, 03:36:22 pm
content: I'm just running a wash load now and all seems to be functioning normally. Spin is working, the water solenoids seem to be working, I hear water going in. So the relays are ok. The timer is counting down and steps in the cycle are progressing. If there was an issue with the control board, it doesn't seem to be having any effect, so the components look to have been spared.I was lucky. I fully expected to have to pull out the multimeter on this one, but as it turns out, an alcohol cleanup of those burn-dendritic patterns from the 2-sided board vias in the high voltage side did the trick (see photos Washer5 to washer9).

author: edy
author_rank: Super Contributor
timestamp: August 05, 2014, 01:06:18 pm
content: Hi everyone, so far the washer seems to work. I decided to put together a video slide-show for people on YouTube in case anyone else runs into a similar problem. I am still surprised nothing fried and that all that was needed to remove the "short circuit"-causing residue was a bit of isopropanol.

author: mij59
author_rank: Frequent Contributor
timestamp: August 05, 2014, 01:27:54 pm
content: Hi,You could use a conformal coating to protect the pcb.

author: edy
author_rank: Super Contributor
timestamp: August 05, 2014, 03:25:37 pm
content: Hi mij59,Thanks, that is a good idea. I am thinking this area is likely to get soiled again over time and a coating will help. I assume it doesn't matter about the high voltage and conformal coatings are designed to be insulative even at high voltages? I found some at a local electronics store I use:http://www.sayal.com/zinc/zinc_SEARCH.asp?txtSEARCH=185193Maybe I can get this stuff and paint the board with it. Hopefully I won't mess things up. Any down-side to using it? I imagine it may make it more difficult to solder or replace components in the future, but hopefully I won't have to if it is doing the job and protecting things.

author: mij59
author_rank: Frequent Contributor
timestamp: August 05, 2014, 04:20:16 pm
content: Quote from: edy on August 05, 2014, 03:25:37 pmYes removing the stuff can be a problem e.g. epoxy or poly urethane coatings, maybe a spay on silicone base could also do the job.http://uk.rs-online.com/web/p/conformal-coatings/0494714/] http://uk.rs-online.com/web/p/conformal-coatings/0494714/

author: IanB
author_rank: Super Contributor
timestamp: August 05, 2014, 04:25:48 pm
content: Might be simpler just to install some kind of shield or splash guard between the source of water splashes and the circuit board?Putting a coating on a board will always make board rework more complicated in the future if ever it is needed.

author: edy
author_rank: Super Contributor
timestamp: August 05, 2014, 06:32:53 pm
content: I could just add a ribbon of silicone right around the joint where the two halves of the plastic moulding that houses the board fit together. At least I can easily peel off the silicone in the future if I need to open it up again.I am not sure how long these appliances are supposed to "last" and what kind of life expectancy parts have. You'd think it should be 10-15 years or more. Seems like every 5 years or so, I should be opening them up anyways for a basic maintenance/cleanup/inspection.On the other hand, some flat TV brands these days have been experiencing issues much sooner than 10-15 years, and people seem to have no qualms about chucking them out and buying a new one, maybe because they perceive the technology is better and they wanted an "upgrade" anyways. Still I feel there is something fundamentally wrong with a product failing that soon.

author: SeanB
author_rank: Super Contributor
timestamp: August 06, 2014, 03:42:54 pm
content: My first washing machine was a Hoover twin tub, it was about 30 years old when I got it, and I had it for a few years before selling it on. It was cheap to run, and spares are still plentiful and cheap. I think you could probably build the complete machine from the spare parts available locally for it, the only thing not available is the case.my second one was a30 year old AEG Lavamat Deluxe electronic, dating from the 1970's, complete with custom microcontroller and electronic speed control. i scrapped that one after about 15 years as I could only get spares ( pump and the main bearings) for a cost where a new top loader was about 20% cheaper.Replaced with a LG top loader, and so far the only parts I have needed are a drain pump (common failing on these models) which cost me $10 last week. Been running now ( touch wood) for about 10 years now.