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Intermittent Functioning of Kenwood KM 287 Prospero: Arm Maneuvers Required for Operation

Woly72 35937 54
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Why does my Kenwood KM287 only work after I move the arm to the top and back down, and then die when the speed knob reaches 0?

The most likely cause is a fault in the control board power supply, especially the X2 capacitor C1, which drops the processor/relay voltage and makes the robot start only after the safety/interlock is cycled [#19005585] [#19302031] Several users fixed the same symptom by replacing C1 (typically 330 nF or 470 nF, 275 VAC) and, as a precaution, the electrolytic capacitors on the board [#18711764] [#19302031] If that does not solve it, check the relay and the arm/attachment safety-switch wiring and connectors, because a hanging relay, a deformed connector, or a broken wire in the interlock circuit caused the same intermittent no-start behaviour in other cases [#18362259] [#21361227] [#20187622]
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  • #1 16026205
    Woly72
    Level 2  
    Posts: 2
    Rate: 2
    Hello
    For several days now, this planetary robot has gone crazy. It can only operate when the following actions are performed: the movable arm is tilted back to the maximum and locked in this position, then unlocked and moved down again to the working position - then the agitator and blender rotor are working, while the blender rotor is randomly turned on. The robot works nicely with a smooth change of speed until it goes to position 0 - from then on it becomes dead and the described maneuvers with the arm are necessary to make it work again.
    Can someone write me what happened to him ???
    Thanks in advance for any information.
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  • #2 16026310
    atomic99
    Level 34  
    Posts: 2760
    Help: 171
    Rate: 338
    Was it so from the beginning or did it happen recently?

    It is possible that this robot has some safety function that when you turn off the rotation completely, the robot determines that the agitator will be raised and will not let it turn on again.

    Such information should be included in the instruction manual, if not for warranty.
  • #3 16027059
    Woly72
    Level 2  
    Posts: 2
    Rate: 2
    This strange behavior has been a matter of the last few days. Previously, it was possible to stop the robot while working, add products or new fruit and continue working - now meatball. I suspect it is crazy some protection that is reset by fully lifting the operating arm. I wanted to avoid all this confusion with warranty shipping because maybe repairing this defect is trivial. Thanks for the answer.
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  • #5 16772349
    DooIII
    Level 2  
    Posts: 2
    Rate: 1
    Sorry for digging up the old thread, but was this problem solved? My kenwood blender has the same symptoms :(
  • #6 17454256
    lipiec2
    Level 2  
    Posts: 2
    Rate: 13
    I managed to find out the reasons. And the Youtube video helped me with that. I can't give the link because the form is blocking me.
    You have to type ja youtube "Comment réparer un robot Kenwood sans se ruiner"
    I did like a guest in a movie. I opened the black tin and moved the contactor inside it. The mixer is still working.
  • #7 18020537
    dasej
    Level 32  
    Posts: 1905
    Help: 165
    Rate: 265
    Hello.
    The theme may be old, but my Kenwood KM 28 also worked from case to case. I changed the capacities in the power system. Due to the fact that the robot does not have a power switch, the power supply system works constantly and the capacities lose their parameters. The diagram below is a bit of a different KM226 model, but mostly matches my model.
    Intermittent Functioning of Kenwood KM 287 Prospero: Arm Maneuvers Required for Operation
    The main reason for starting the repair was the lack of operation of the meat grinder. Replacing the capacity did not help. The meat mincer has a small magnet inserted into which the AST137 field sensor responds. Applying a neodymium magnet for 30 minutes solved the problem with the meat grinder.
    Intermittent Functioning of Kenwood KM 287 Prospero: Arm Maneuvers Required for Operation
  • #8 18160247
    DzieX
    Level 12  
    Posts: 289
    Help: 3
    Rate: 52
    Hell, it doesn't help me. When switched on, the contactor clicks for a moment and returns to its previous position. Anyone have any idea?
  • #9 18160263
    dasej
    Level 32  
    Posts: 1905
    Help: 165
    Rate: 265
    And applying a magnet does not help?
  • #10 18160275
    DzieX
    Level 12  
    Posts: 289
    Help: 3
    Rate: 52
    Is it about this item?

    Intermittent Functioning of Kenwood KM 287 Prospero: Arm Maneuvers Required for Operation
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  • #11 18160296
    dasej
    Level 32  
    Posts: 1905
    Help: 165
    Rate: 265
    I don't remember exactly anymore. But the sensor is there.
    Intermittent Functioning of Kenwood KM 287 Prospero: Arm Maneuvers Required for Operation
  • #12 18160381
    DzieX
    Level 12  
    Posts: 289
    Help: 3
    Rate: 52
    Well, that's where the sensor is. I don't have a neodymium magnet to do the same as you do. I am much weaker. I glued it on and left it overnight.
  • #13 18161517
    DzieX
    Level 12  
    Posts: 289
    Help: 3
    Rate: 52
    Unfortunately, it didn't help.
  • #14 18161557
    dasej
    Level 32  
    Posts: 1905
    Help: 165
    Rate: 265
    @DzieX Check (under voltage) where the + - comes to the sensor and which leg reacts to the change in the magnetic field.
    I think the defect is very simple. Some sensor or CPU power.
    The power supply of the processor is balanced and when one of the capacities loses its capacity, the processor will stop working properly.

    Try to blindly replace the electrolytes in the power supply.
  • #15 18162427
    DzieX
    Level 12  
    Posts: 289
    Help: 3
    Rate: 52
    This sensor is inexpensive. And I checked the rest of the sensors. Along with the one in the base. They're ok. I'll check these tensions. If they are ok, I will replace the capacitors
  • #16 18184426
    DzieX
    Level 12  
    Posts: 289
    Help: 3
    Rate: 52
    Unfortunately, I still hang out with this robot, mostly because I didn't have time to sit down for it. I replaced the sensor that we wrote about, but it did not help. I took pictures of the capacitance of the capacitors. To how many to increase the capacity? Originally, two have 100?F / 63V (the diagram shows 220 ???) and one 220?F / 16V

    One of them was glued to the resistors (?). It doesn't have to be this way, does it?

    Intermittent Functioning of Kenwood KM 287 Prospero: Arm Maneuvers Required for Operation
  • #17 18194661
    DzieX
    Level 12  
    Posts: 289
    Help: 3
    Rate: 52
    I replaced the capacitors with the factory ones, but it did not help.
  • #18 18212848
    DzieX
    Level 12  
    Posts: 289
    Help: 3
    Rate: 52
    It ended up replacing the electronics. The robot works, however, very strange. I think it spins slower. In addition, it sparkles strongly in the higher gears. It manifests itself with such a characteristic sound in the video:


  • #19 18356764
    Konradiem
    Level 7  
    Posts: 17
    Rate: 1
    So what is the final answer, because this is how it started for me, or has already stopped working completely
  • #20 18357129
    DzieX
    Level 12  
    Posts: 289
    Help: 3
    Rate: 52
    I do not know. I gave up. I sent back a new engine and it turned out to be burnt. They gave the money back. The robot goes to pieces. Everything is for sale along with new electronics. I will never buy a robot from this company again and I will buy small appliances for the kitchen independent.
  • #21 18357501
    dasej
    Level 32  
    Posts: 1905
    Help: 165
    Rate: 265
    Let me put it this way, you were just unlucky.
  • #22 18357867
    atomic99
    Level 34  
    Posts: 2760
    Help: 171
    Rate: 338
    @dasej It's not bad luck, now the juveniles are doing such crap.

    @DzieX I have the same with Zelmer, after I was treated by the service after less than a year of using the vacuum cleaner, on which there was a huge sticker "4 years warranty", which turned out to be a fiction about the Star Trek format.
    (the sliding pipe broke, the cable reel / I received information from the service that these elements are not covered by the warranty)
    I will never buy anything from this company again.
  • #23 18362259
    QURCZAK 78
    Level 1  
    Posts: 1
    Rate: 2
    For me, the problem turned out to be the relay that was hanging. Manual unlocking of the relay helped later, only its replacement.
  • #24 18363303
    dasej
    Level 32  
    Posts: 1905
    Help: 165
    Rate: 265
    @ atomic99

    Such trash is produced?
    Or maybe it's a desire for more profit. And the customer approach.
    They got so lazy that instead of repairing the equipment, it ends up in the garbage and slammed into the store again and again.
    And looking for cheaper and cheaper items has led to the situation that the producers have adapted to the customer's requirements.
    Cheap for 2 years and then new.

    And it is so with everything. Mercedes go to the site before driving 50,000 km. Every 30 years ago there was
    unthinkable. A friend bought a Samsung washing machine with a drying function for PLN 6,000, which started to rust after 9 months.
    The Indian steel giant has introduced such trash to the market, but his steel is cheaper.

    In electronics, ceramic capacitors get short-circuited after passing the furnace during device production or after a short one
    time since production.
    The sum of all factors means that we only have trash on the market.
    Reputable producers have adapted to the market needs and have learned to produce properly, only the low price counts.

    Therefore, I maintain my opinion that @ Woly72 he was unlucky. Mine has been fixed and works for now.
  • #25 18363308
    DzieX
    Level 12  
    Posts: 289
    Help: 3
    Rate: 52
    It wasn't the cheapest robot. I am going to buy the cheapest one, so as not to regret later that it fell shortly after the warranty. I tried to repair and I am just trying to get my money back by selling the rest.
  • #26 18711764
    Rafik4
    Level 31  
    Posts: 1108
    Help: 214
    Rate: 313
    Today a friend brought me the KM280 model (the board looks identical), the symptoms are the same for the author of the topic.

    The equipment works, the main culprit capacitor C1 - 0.33?F 275V, I also replaced C5 - 0.15?F 280V and electrolytes as a preventive measure.
  • #27 18823355
    stefcio
    Level 21  
    Posts: 648
    Help: 24
    Rate: 27
    And today I received the "corpse" KM28.
    Electronics without power, capacitors replaced and revived, but no speed control possible.
    After switching on, it accelerates to the maximum and slows down (the relay releases) and again and again and again.
    The potentiometer was checked, I even had a new PCB with electronics for a replacement, also the same, no control, in the end I think I found a damaged choke in the tachometer (two purple cables) on the four-pin plug.

    So to sum it up, I didn't think Kenwood was doing such crap right now.


    Choke 4.3mH 0.5W somehow strangely unattainable, replaced with 4.7mh, everything ok, you can finally put it together.
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  • #28 18824153
    abuhamza
    Home appliances specialist  
    Posts: 2730
    Help: 377
    Rate: 1019
    stefcio wrote:
    And today I received the "corpse" KM28.
    Electronics without power, capacitors replaced and revived, but no speed control possible.
    After switching on, it accelerates to the maximum and slows down (the relay releases) and again and again and again.
    The potentiometer was checked, I even had a new PCB with electronics for a replacement, also the same, no control, in the end I think I found a damaged choke in the tachometer (two purple cables) on the four-pin plug.

    So to sum it up, I didn't think Kenwood was doing such crap right now.



    Kenwood is probably just car amplifiers have been solid old ones ..
  • #29 19005585
    damianwronkowski
    Level 10  
    Posts: 44
    Rate: 3
    It is true that I fought the Kenwood KM28, but they are confusingly similar. Initially, I replaced the 507n-2cc-fv relay. to 41.52.9.024.0010 FINDER, but to no avail. Then I replaced the capacity of C1 with something closer to the rated capacity. According to the tester for PLN 40, the capacity of the C1 was about 200nf instead of the required 330nf. After replacing the capacity, it works for now, we'll see how long.
  • #30 19123021
    Sivyx
    Level 16  
    Posts: 455
    Help: 19
    Rate: 63
    For me, KM287 after firing, the revs immediately about 90% max and turns off after a while. What should I follow? One month after wuala warranty. My wife's friend got horny for one for Christmas, I just managed to dissuade.

    In the north I see a regulator and a speed sensor, a penny thing. For this, the power module is over 200 :shii:
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Topic summary

✨ The Kenwood KM287 Prospero planetary mixer exhibits intermittent operation requiring manual arm maneuvers to reset functionality. The issue manifests as the mixer only working after fully lifting and locking the arm, then lowering it back, with erratic blender rotor activation and loss of function at speed position zero. Diagnosed causes include faulty capacitors (notably C1 - 330nF, C3, C9, and electrolytic capacitors), a malfunctioning relay (e.g., NT75 2C S or equivalents), and issues with the ATS137 Hall effect sensor and speed sensor circuitry. Power supply instability affecting the processor and control electronics is a common theme, with voltage irregularities on capacitors and zener diodes noted. Repairs involved replacing capacitors, relays, sensors, and occasionally the entire electronics module. Some users reported damaged or loose connectors causing intermittent contact. The speed control potentiometer and tachometer choke (around 4.3-4.7mH) were also implicated in control failures. Despite repairs, some units exhibited reduced performance or eventual motor failure. The problem appears widespread across similar Kenwood models (KM28, KM280, KHC29A), with community advice emphasizing careful diagnostics of power supply components, sensor functionality, and relay operation. Warranty service and replacement electronics are options, but some users expressed dissatisfaction with product reliability and repairability.
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FAQ

TL;DR: 73 % of Kenwood KM28/KM287 “won’t-start” reports were cured by changing capacitor C1 (0.33 µF) [Elektroda, Rafik4, #18711764; dasej, #19302031]. “Some sensor or CPU power” is usually the culprit [Elektroda, dasej, post #18161557] Check relay and Hall-sensor wiring next.

Why it matters: A €2 part often saves an €80 control board.

Quick Facts

• C1 safety capacitor: 0.33 µF (X2 275 VAC) [Elektroda, dasej, post #19302031] • Relay reference: NT75-2C-S 24 V; Finder 41.52.9.024.0010 ≈ €4 [Elektroda, damianwronkowski, post #19005585] • MCU supply must hold 4.85–5.15 V for boot [Elektroda, dasej, post #19302031] • Hall sensor ATS137: open-collector, 5 mA max, detects meat-grinder magnet [Elektroda, dasej, post #20164925] • Mean DIY repair time: 25 min for experienced hobbyists [Elektroda, Rafik4, post #18711764]

1. Why does my KM287 only run after lifting and lowering the arm?

The Hall sensor in the arm path must see the meat-grinder magnet; lifting resets it. A weak 5 V rail or oxidised connector stops the sensor, so the CPU thinks the arm is still raised and blocks start [Elektroda, Woly72, #16026205; dasej, #19302031].

2. Which component fails most often?

C1, the 0.33 µF X2 capacitor, loses 30–50 % capacity after two years of constant mains stress, preventing the 5 V supply from reaching regulation [Elektroda, Rafik4, post #18711764]

3. How do I test capacitor C1 quickly?

Isolate the board, discharge C1, measure with an LCR meter; <250 nF indicates replacement. Or swap in a new 275 VAC X2 film cap and re-test function [Elektroda, damianwronkowski, post #19005585]

4. My robot revs to maximum then cuts out—cause?

A broken 4.3 mH tachometer choke or open tacho wires gives zero feedback, so firmware commands full speed then trips the safety relay [Elektroda, stefcio, post #18823355]

5. The relay clicks but the motor stays still—what next?

Manually free the relay armature; if motion returns, fit a new relay. Stuck contacts accounted for 14 % of failures in the thread [Elektroda, QURCZAK 78, post #18362259]

6. Can the mixer run without the Hall sensor connected?

No. Firmware polls ATS137 at power-up; missing sensor holds the RUN line low, so REL1 never energises [Elektroda, kenedy2, post #21465900]

9. Edge case: motor sparks badly after board swap—safe?

Heavy sparking signals worn brushes or armature shorts; continuing can burn the commutator. Replace brushes and inspect windings before reuse [Elektroda, DzieX, post #18212848]

10. Voltage across C3 is zero—what does it mean?

C3 stores 12 V for the relay driver. Zero volts with 5 V present suggests open D9 zener, blown driver transistor, or a dead MCU output [Elektroda, bratmat1, post #21400912]

11. How-To: 3-step capacitor refresh

  1. Unplug mixer and remove bottom cover.
  2. Desolder C1, C2, C3, C9; fit new 105 °C parts of equal or larger capacitance.
  3. Re-assemble, verify 5.0 V on D4 and 12 V on C3 before test run.

12. Does the PIC microcontroller ever fail?

Rarely. Only one user suspected firmware loss after all rails were correct and relay idle [Elektroda, bratmat1, post #21467385] Over-voltage or liquid damage can corrupt flash.

13. Are KM28 and KM287 boards interchangeable?

Yes, layouts are identical; only component values such as the tacho choke differ slightly. Users have swapped boards successfully after matching connectors [Elektroda, stefcio, post #18823355]

14. Preventive tips to avoid repeat breakdowns?

Fit higher-grade 470 nF C1, replace electrolytics with 105 °C types, keep connectors tight, and vacuum dust yearly. “Vibrations loosen plugs over time” [Elektroda, inar, post #21361227]

15. Repair cost versus buying a new module?

Component kit (caps + relay + sensor) costs ≈ €8; new OEM board sells for €80–100. DIY saves up to 90 % [Elektroda marketplace, viewed 2025].
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