Our replacement Krups KM7000 coffee maker has once again bit the bullet, a mere 101 days since we got this replacement. One day it was grinding and brewing perfectly, the next day it was only grinding, with all brewing and heating functions non-existent; the same symptom it had last time. As promised from last time this thing broke, I pulled out my tool box and tore into this warranty-expired-machine. The guts of the machine are pretty easy to get to with a bunch of phillips screws holding the bottom together. There is one triangle shaped screw head, which I guess is to keep users from tampering with the insides, but I was able to remove it with a precision flat-head screwdriver.

The electronics of the coffeemaker aren't too complicated, even though you might expect something more befitting its $150 price tag. A visit to the Krups support site tells you that nothing in the machine is "user-replaceable". Irregardless, I'm an engineer, so I was gonna get to the bottom of why part of the machine worked, and only the heating functions were broken.

Pulling out my trusty voltmeter, I started looking for wires and fuses that were broken. The circuit board looked intact, and though it was some simple circuitry, it looked like this would be the last thing to fail in the entire unit.

I started disassembling it and found two little tablet looking components, wired inline with the heating element. From the markings on them, I found out they were thermal fuses manufactured by "Therm-o-disc". Both of them are from their "Microtemp G4A00" series of thermal fuses (spec sheet). One is rated to 240C, the other to 216C. I checked the resistance on them with the multimeter. The 216 fuse was still intact, but the 240 fuse had blown wide open.

So I did a quick experiment. Using alligator clips, I bypassed the fuse so that current could flow across the wire, and turned on the coffee maker. I put some water into the reservoir and waited a few seconds. Lo and behold, the machine started brewing!

Initially I just wanted to keep it like this and get on with my life. But I asked my dad (a certified electrical engineer) about this and he said I shouldn't risk it. The thermal fuse is a safety device to prevent your coffeemaker from overheating, melting the plastic, and subsequently burning the house down. So I went online and looked for these Therm-o-disc fuses. Ended up buying four of each at $1.25 per fuse from www.goodmans.net. I guess a buck-twenty-five is a reasonable amount of money to spend to prevent your house from going up in flames.

So, did the machine malfunction and blow the thermal fuse? I don't think so. With two fuses rated at different temperatures, if the higher temp fuse blew, then the lower temp fuse should have also gone too. My guess is that these fuses aren't made very well and over time they just degrade, opening the circuit and turning your coffeemaker into a useless plastic brick.

2/3/2010 Update: After receiving the replacement fuse from www.goodmans.net, everything is put back together and working perfectly. Been brewing coffee for the last two days. No problems whatsoever.

4/20/2010 Update: For a more detailed teardown of the Krups KM7000 coffeemaker, and a better description of the replacement procedure for the thermal fuses, check out Mark Kolich's write-up. Mark contacted me last month about this repair, and documented everything much better that I could have done.

6/7/2010 Update: The grinder in the unit stopped working a few months after this post was written. I managed to fix that as well. See the tear-down here.