I was recently gifted a problem MES 30 with rear controls & window, model #20070411. It has the random shutdown, shutoff problem
which was never able to be fixed even after multiple control unit changes. Wanting to get to the bottom of the problem, I took it completely
apart and reverse engineered the electronics. I discovered that the internal power supply is being overloaded by design. This and poor
power distribution push it over the edge. The box is designed with a little power supply and relay board in the bottom that connects via
a long cable to the control unit on top. The control unit gets +5V power through the cable. With everything turned on, the little
power supply is overloaded beyond rated capacity. Then large power demand spikes come in from the control unit and relays which push the
voltage down hard just for an instant. When the voltage goes down hard enough, the control unit resets itself ending the smoke and
giving you a bad surprise when you wake up. This is compounded by trying to run power to the control unit through a long thin wire
and no large decoupling capacitors in the control unit.
The whole design is on the edge. When you call customer service and they send out a new control unit, it's just luck that the new
Control unit + Box combination pulls it back from the edge enough to work. Over time ageing will push it back over the edge after
you're out of warranty. That was the experience of my boxes previous owner. Other symptoms of the problem are shutting down
when changing temperature, changing time or turning on the light.
I worked up a fix that seems to work, add a large capacitor to the control unit. The capacitor holds the voltage up enough during
brown outs to avoid reset. It's easy to take the back off the control unit and get to the spot on the board to add the capacitor.
These pictures show where it is. I ended up with 1000uF just because I had a bunch laying around. It just needs a big cap.
You can get caps on ebay. To get a little more soldering room to attach the cap leads, scrape some of the green coating off the
board to expose bare copper. The left lead is Ground, the right is +V. A 10V or higher capacitor is fine.
Edited by James95014 - 7/19/16 at 12:15pm