Regarding an electronic control board design for an electric dryer - Page 1
Forum section: electronics / general

author: xrunner
author_rank: Super Contributor
timestamp: November 06, 2022, 12:49:37 pm
content: My 19 year old Maytag Neptune electric dryer (MDE5500AYW) stopped working last week, meaning the control panel was dead. When I researched the possible issue there was a 3300 uF 50 V electrolytic cap that usually failed, so I pulled the board and I did find that cap was bulged and replaced it. That made the board work but after a while it got very hot and shut itself off, so there was another failure on the board and I don't have a schematic or time to bother with it since there are used boards for sale.What I noticed when I had the board out is that four high-wattage resistors on the top of the board were very "charred" and they had obviously got very hot. Even the white plastic close by gets brown by the heat. Was that the failure that happened to my control board? Well, they had got very hot, but apparently every used control board out there is like the picture attached. The attached pics of a 100% working board for sale (mounted on the plastic carrier) and my board on my bench (two caps removed for testing). All the used ones are the same where those resistors are - charred. If you can find a pic of a new one (which are not available any longer) they do not have charred resistors (duh).I ordered a reasonably priced used board on Ebay (same charred resistors) and installed it, and now the dryer works as it has since I bought it. But being curious, I wanted to know if the resistors were hot. I checked with an IR thermometer and yes they were hot, around 82 C or 180 F. But ... surely when I turned the dryer "OFF" from the control panel the resistors would cool off ... no - they do not. They stay the same temp as long as the dryer has electric power from the outlet. The main IC is a Sharp LU850703 but I haven't found info on it.So for 19 years, even when off, these resistors are that hot 24 / 7 / 365. It looks like they have an input from a 24 VDC regulator, but the question in my mind is, what kind of crap design burns that kind of power just to wait for the user to touch the control panel and select the way they want to dry clothes? Is this typical of designs ~20 years ago that they just didn't care about poor energy efficiency? Is it a bad design from the get-go? Even if they want to burn power in standby, they didn't pick the right wattage resistors (did they?). How could they think this design was OK to ship in a new product?Oh - but what about the matching Maytag Neptune washer? Is it warm around the area where the control board is, when turned off? I didn't take it apart but yes - it is warm up top when turned off. So from now on, when I finish washing and drying a load of clothes, I'm going to switch the circuit breakers for these appliances off until I need them again in 3 or 4 days (I'm single and don't have a lot of clothes to wash and dry).Thoughts on this are welcome.

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 06, 2022, 02:35:17 pm
content: I think energy efficiency standards for clothes dryers are a relatively new thing. Energy Star really dropped the ball on that one, adding a simple heat exchanger would give a very substantial boost in efficiency.