I have a B66 that has been working with no problems for over 2 years. Recently, we woke up to find that it's menu was blank, and the machine was completely unresponsive. After I wrote this (apologetically) lengthy post, I found that shocktube had already experienced this problem and solution and posted it in this thread [mod note: see here
], but I still think that the details I recorded could help explain some things.
Initially, I found that the transformer had an open primary winding. I located this post http://www.fixya.com/support/t8104596-need_14_5_volt
that was a great help because as a result of it I found that my transformer was repairable. I determined that the thermal fuse inside the transformer was bad. Because the fellow on FIXYA apparently lost track of the winding connection when he dug too deep to remove the thermal fuse, I decided it was unnecessary to remove it since it was open and effectively no longer existed anyway. I stopped peeling when I got access to the wires - there are 3 of them - and checked them with a meter to see where to connect my new thermal fuse. I went with his suggestion and used the Radio Shack 270-1322. I covered it with heat shrink to prevent shorting and placed it against the metal transformer frame.
After this, the Keurig worked just fine, until it started to get confused and kept reverting to the MENU display that has the setup options, instead of staying in the brew menu. I checked the transformer and found it was very hot. Was the transformer bad? After measuring it's current output with a clamp-on current meter and finding that it was very high, I started looking elsewhere - shorted bridge diode or regulator in the regulator/driver board? No. In desperation, I finally started unplugging some of the smaller connectors on this board while monitoring the transformer current output. When I unplugged what turned out to be one of the solenoid valves, the current draw went down tremendously. So the culprit was really the solenoid valve and not the transformer - the thermal fuse just did it's job like it was supposed to.
There are 2 valves, both P/N SH-V0829BC-R(C1) DC12V. 100mA. 0929. The one that is tee'd into the water supply line to the hot water tank started to intermittently short out and draw a lot of current, as much as 850 mA, but both the current and resistance would fluctuate. The lowest observed resistance was about 8 ohms (WAY too low). This exceeded the current capacity of the voltage regulator, but fortunately it never failed. The poor transformer, which is rated for no more than 470 mA on it's secondary, was putting out as much as 1.5 amps due to the load of the valve shorting out. The display won't stay in the brew menu when this is happening. Instead, it keeps reverting to the MENU display that has the setup options. This happens because the main 12V supply is being drug down so low that the brain gets confused (it measured about 8 volts at one point). As the short got worse, the display got very dim. Unplugging this valve would immediately clear the problem and the machine would appear to work fine. The valve never leaked at all, and functioned just fine otherwise since I could hear it clicking. You had to look twice to see the small amount of brown corrosion at the periphery of the seal at the terminal lug end of the valve. This is another case of moisture leakage on these valves that were not designed for fluids, only this time it resulted in the valve shorting itself out.
When the valve would short, it would get very hot and so would the transformer. My new thermal fuse should have blown, but in it's new position I apparently couldn't provide enough heat conductivity to it. I had to enclose the thermal fuse with heat shrink because it's case is electrically connected to one of the leads; perhaps this insulated it from the transformer heat too much. I began to realize that because of this, none of the electronics from the power supply through to the control circuit and valves had any protection whatsoever, should something like this happen again. Since I had a 500 mA slow blow fuse handy (and even a fuse holder for it) I cut one of the the blue secondary leads of the transformer and inserted the fuse in series there. The transformer is rated at 470 mA maximum, so the 500 mA fuse is holding fine, but I have confidence that it will blow if it ever needs to.
Note that this failure happened at night, WITH THE MACHINE TURNED COMPLETELY OFF. Other people have posted that they have woke up to a dead coffee machine as well. Normally the transformer and power supply are constantly operating, even with the machine shut off, and so are the two valves. So here is the scenario: In the middle of the night, the valve not only shorts out but gets very hot. So does the voltage regulator and transformer. If not for the thermal fuse inside the transformer, there could eventually be smoke.
My advice to anyone whose machine has a menu that seems confused, unresponsive, or dim: Check the temperature of the two solenoid valves. They should feel warm, but not hot enough to burn your fingers. I know that other things can cause unresponsiveness, but this is a simple check if you already have the machine apart.
While I had the machine apart I opened the water pump. It was in perfect condition. Since I had disconnected the pump, I pulled the check valve out and cleaned the tiny bit of buildup out of it with a long cleaning Q-tip. I pulled the black disk shaped mesh filter out and cleaned it with a strong stream of water. I had a similar one of these in my riding lawn mower and cleaned it the same way. Since it just has a metal screen inside, it is cleanable and reusable this way.
I bought 3 of the SH-V0829BC valves from Skycraft Parts and they all tested OK. They come with cut vinyl tubes still installed, so they really were cut out of equipment - not new. However, Skycraft says that they were cut out of equipment that was never put into service, whatever that means. The one I installed in the machine has been working fine for a week now as of this writing