Microwave oven switching issue

Discussion in 'The Projects Forum' started by hafcanadian, Oct 30, 2013.

  1. hafcanadian

    Thread Starter New Member

    Mar 22, 2010

    I read a thread here from a couple of years ago, which had a resolution, but opted not to "bump" it due to its age and possible differences in causation.

    Our 1994-era Sharp convection microwave has had a problem for several years maintaining its operation. It's been into the service facility a couple of times where they couldn't find a problem, but charged for looking. Which is why I've had it apart numerous times, thinking it was a bad microswitch initially, than zeroing in on the circuit board or touchpad. Not being an electronics expert means I've been spinning my wheels.

    When it is started, it may or may not actually provide microwaves. And if it does start okay, it may quit somewhere along the line during the cooking process. When it acts up, the fan runs and the turntable turns, but the overhead light goes out and you can hear no magnetron or whatever the device is that makes noise when it's actually cooking. At first I thought sure it was one of the latching switches, as pushing the door a bit often restarted the light and cooking. Removing the cowling and repositioning latch switches didn't seem to work at first, but I'd tweaked the door hinge at one time to realign it, and that's when the problems started; so I put the door back as it was, sagging very slightly out of line with the frame. This seemed to work... for a while. Then it started again. I tweaked switches and it seemed to resolve... for a while.

    Yadda, Yadda. The switches all click on and off cleanly and don't seem dirty. They engage properly when the door closes. So the last couple of times I tried to remove and check the circuit board, because we've discovered that if we press or firmly tap precisely a certain blank spot on the control pad, the light will come on and the cooking start or resume. The hassle is it is unreliable, so we have to stand there and watch it in case we need to press on the "hot spot", cuz out of the blue the light goes out and cooking stops, although you can hear the fan running, just not the heavier electronic motor sound of microwaving.

    I can't find anything wrong with the board except for one diode that is slightly darkened. The hint is that this diode is precisely behind that point on the control panel which is the "hot spot", where if we press we can keep the cooking going. My problem is that the touchpad is between the panel front and the circuit board, and I don't exactly see how pressing the panel front would affect the board, aside from exerting some slight pressure on the overall board via its mounting. I'd take the touchpad apart, but I can't figure out how to disassemble it - its plastic housing seems to clip together inside.

    Sharp still makes almost the same model, but it is $600. The only other unit that almost exactly fits in the same cabinet (over our oven) such that I could reuse the existing Sharp metal trim is an $800+ Bosch. After years of tolerating this thing, I'd like to offer the family a less aggravating time in the kitchen, but money is not available now. Should I just try replacing the suspicious diode, or does anyone know how to pry the touchpad apart so I can inspect it? If needed, I can take the unit apart again and try to supply photographs of it, the circuit board, and the wiring diagram inside, though posting images in forum threads isn't always a successful venture.

  2. wayneh


    Sep 9, 2010
    I don't know if it's relevant to your situation, but the fancy touchpad on my Jenn-Air oven eventually became unusable. The dummies mounted it where moisture leaving the oven would pass right through the electronics, and that's not good for touch pads. And they used one of those cursed ribbon cables that are nearly impossible to work on or repair.

    No replacements are available anymore, so I brute-forced a solution by installing a small pushbutton in each pad location on the touchpad, and wired these back to the control board. It's held for several years so far, much better than I'd hoped.