Repairing a Kenwood Titanium Chef Patissier XL KWL90 (E:24 error)
Electronics, Repairs ·Introduction
This time, we have a fairly expensive food processor from Kenwood - a Titanium Chef Patissier XL KWL90 to be specific. It seems to be very well built - certainly upper class for home use and maybe even suited for moderate commercial use I could imagine. Certainly an item worth taking a good look.
The problem
The machine can be turned on normally, but even with very light use, after a few minutes, it stops and shows an error message:
This fault apparently relates to “motor overload or internal sensor/control board fault”, but no really concrete error code book or what to do seems to be available on the internet.
Investigation
Without further clues, let’s take it apart and see if we can spot anything. As this is a well-known and expensive machine, you can find disassembly videos on the internet, maybe worth watching to see in which order certain things need to be done. The bottom comes off easily:
And reveals the main circuit board.
Looking at the silkscreen legends on the PCB, one connector at the bottom with a grey 2-way cable (highlighted in red) immediately attracted my attention because it says “Motor NTC”. Looking at the other cabling, there is only a thick power connection, a 3-way hall sensor connection and this NTC cable that connects the motor assembly.
The grey wires measure around 100kOhm with a Multimeter which seems ok, indicating a 100k nominal-valued NTC. At this point the plan was to re-assemble the machine but leave the bottom open, turn it on and let it run until the fault occurs. I then quickly disconnected the power and the sensor and measured its value to see what was going on here: voila - an open circuit! That is weired, because I would have expected a somewhat lower resistance due to the motor heating (negative temperature coefficient - NTC). An open circuit very well explains the observed issue.
So where is it coming from? Let’s get the motor out from the motor assembly.
The NTC is contained in a heatshrink tube and cable-tied to a motor winding. Somewhere there must be a problem - either the NTC itself or the connections.
The fault
After some poking around with the multimeter, it turned out that the NTC worked fine, and the fault was narrowed down to this crimp-connection:
Wiggling it occasionally makes contact again. Presumably it was not fitted very well already during production, and then due to the motor vibrations it eventually worked its way loose.
The fix
Well, that is easy to fix, just solder the connections to the cable, add some new heatshrink and cable-tie it to the winding again.
Conclusion
The E:24 error was caused by a faulty connection to the NTC that protects the motor from overheating. The connection might have been done a bit sloppy in the factory and eventually worked its way loose due to motor vibrations. After soldering the connections, even with heavy use, the food processor runs again like a charm. That was a rather straight-forward repair this time.