Symptoms: At first it started making weaker and weaker coffee. We thought it was the grinds. We thought the basket was clogged. On day, it just didn't perk at all.
Solution: Fix it! This Instructable explains how we got it back into working order by opening it up, replacing a thermal cut-off (like a fuse or switch), and reassembling it. Now it makes coffee again!
Note: This Instructable might also be applied to cordless electric kettles, as I think they may work in a similar fashion.
The items you'll need are:
- Phillips screw drivers
- Replacement parts (in this case, a thermal cut-off)
- Soldering iron and solder
- Needle-nose pliers
- Thermal paste (may not be needed if the thermocouples aren't disturbed)
- Crazy glue (if you brake a plastic piece like I did)
Special thanks to Robin and Paul, is was a team effort to fix this puppy!
Step 1: How the Percolator Coffee Maker Works
- The pot sits on top of the power base, and once connected to an electric outlet, electricity moves from the power base to a conductive metal "cup" in the pot. The resistance heats the water, bringing it to a boil.
- Once boiling, bubbles of gaseous water force hot liquid water up the pump tube, and it rains down on the basket filled with coffee grinds (this is the "perking" action).
- The perking cycle is completed when an appropriate temperature is reached, and the boiling is stopped. This is the important point. It is here that a thermal cut-off trips and tells the machine to stop boiling (it will later reset itself so that coffee can be brewed again).
- The heating switches to a "warming" mode.
- A little orange light comes on to tell you it's coffee time!
This may not be entirely accurate, I am open to corrections on the workings of this machine!
Step 2: Checking the Power Base
The outer ring is the ground, and you can see a little metal tag that contacts the outer ring on the bottom of the coffee pot.
The inner ring and the hole in the centre is where current flows in and out.
Step 3: Removing the Plastic Base From the Stainless Steel Pot
Turned upside down, there are 4 phillip screws that hold the black plastic base onto the stainless steel coffee pot. Unscrewing these screws was easy, but for some reason the little plastic spacers surrounding the screws broke off. Take care that you don't force the screws to remove them. However, it's likely that they were either glued on poorly, or as I discovered putting the thing back together, over-screwing them in probably led to the plastic cracking.
Next, you will see that the small plastic disk which houses the electrical contacts (the metal rings that contact the power base) can be twisted off. Carefully twist this plastic ring until the tabs allow it to to be removed easily from the main base.
Next, the little LED inside a plastic tube that shines through the little orange light can be slipped out easily.
The base is now completely free from the stainless steel pot. Finally, all that needs to be done to get at the inner workings is to unscrew (phillips) the two wide screws that hold the large plastic plate that acts as the support for the main base (note that there are locknuts and washers on these screws, so take care to not loose them).
Step 4: Finding That Broken Part
- A wide metal bracket held to a heavy looking metal "cup" (heating element) by a single wide screw. This bracket holds two thermocouples, one to the heating element and one to the bottom of the pot.
- A thick insulated wire wrapped around the heating element between the cup and the bottom of the coffee pot.
- One little metal bracket that holds a plastic sleeve. This sleeve contains the thermal cut-off.
- Insulated wires and clips that connect it all together.
A small phillips driver can slide between the little hole in the wide metal bracket to unscrew the little bracket that holds the thermal cut-off. It's pretty tricky. You need to also loosen the thick metal bracket to get the plastic sleeve free. It takes a bit of fiddling, and it's really the hardest part of this whole operation. Because the heavy bracket moves the thermocouples, you either need to take them off as well, or wiggle them around. I took mine off completely.
A multi-meter was used to check the continuity of each of the thermocouples and the thermal cut-off. This is where we discovered the thermal cut-off was not working.
*NOTE: always take pictures while dismantling stuff, so that you can remember where everything goes!
I also noticed some corrosion around the heating element. I'm not sure if some coffee was getting through or what. I cleaned it out with a tissue.
Step 5: Replacing the Themal Cut-off
*Taking a picture here is STRONGLY recommended. The thermal cut-off has to go in a specific direction (note the little black or blue epoxy seal on one side).
Once the thermal cut-off was removed, a trip to an electronics store was made and a replacement was found, for $1.75. I also picked up some heat paste to reattach the thermocouples.
The thermal cut-off was rated at 192 degrees C. It was not to exact model of the original, but it was the same temperature rating.
Next, the thermal cut-off was soldered onto the wires. Read the instructions on how to connect the thermal cut-off. It requires that a certain length of leads be left straight, as to not disturb the epoxy seal. Also, it requires the use of a heat sink while soldering. This can be achieved by using a pair of pliers between the thermal cut-off and the area being soldered (so the heat will go into the large pliers, and not damage the epoxy seal).
Step 6: Reassembiling the Coffee Maker
I applied new heat paste to the thermocouples to make sure they had good contact. This was a bit messy, so don't use too much.
I also glued the plastic spacers back onto the plastic base (that broke off during disassembly) with crazy glue.
Finally, put the plastic base back on. You can see there is a notch on the side of the base, that fits into a tab on the side of the stainless steel pot. So it only fits together one way. Carefully screw the four screws back into place.
You're done! Do a test run with plain water to check it out. If you had the same problem I did, you'll probably find that the percolator now seems to perk longer than you remember it. I think the reason for this was that the thermal cut-off was slowly wearing out, and brewing for shorter and shorter periods until it finally just stopped.
Final thing to do, after your test run, is brew up some tasty coffee!