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Thread: Kenwood Food Mixer - No Power - Mint Cond - Dead.

  1. #21
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    It appears to be using a voltage divider based on a capacitor but the larger cap near the hall sensor is the one I'd say. A series choke and a parallel cap is fairly standard to cut the electrical noise that phase shift speed controllers produce in abundance.

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    Right! Just got back from work and read all your great replies. Thank you!

    First: as Nomeat mentioned (photo's included), I checked to see if the Red Connector Socket was giving out 5VDC. Here's where it gets weird...
    As on the photo, when I tested Red to Green I got "OL" VDC and the gas gauge going over 50vdc, when I reversed it I got -4.6VDC.



    The Yellow Cap at this area is reading (in circuit), 0.31uf, so I'm assuming it's ok?



    Hinekadon was asking about the Blue component under the Neutral.


    The Copper Underside:



    I've removed the 'normal' diode and the zenier? diode. Tested them and they are reading ok.

    The Big R205 next to the cap is reading 51Ω
    Last edited by GT250; 10-02-19 at 03:43 PM.

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    Here's where it gets weird...
    As on the photo, when I tested Red to Green I got "OL" VDC and the gas gauge going over 50vdc, when I reversed it I got -4.6VDC. yep thats what i thought . The neg is connected to the neutral . the "yellow " is carrying the tacho pulses from the hall effect to set the speed etc . So if im correct the dcv is on the second white wire . shit i forgotten the circuit i had in my head ????? time to think again damn
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    Were those voltage readings with the cable connected?
    If the voltage collapses when the cable's connected then possibly the PIC has turned itself into a 0 ohm resistor (no smoke left) - tried measuring the PIC's resistance across Vss-Vdd?

    After having a look at the pics:
    Red is the sine wave via 680k resistor for PIC to detect zero crossing etc
    Yellow is the power supply -5V referenced to mains voltage (active)
    Green is the tacho pulses

    So as far as the PIC is concerned, the yellow wire (-5V) is Vss and the mains active is 5V DC higher so Vdd is +5V wrt Vss and all is good even though everything is at mains voltage (but not experiencing mains voltage difference)

    The 5V supply could supply barely enough power for the PIC so just a modest overload would drop it to 0 or too low for the PIC to start up (<3V)
    Ran the numbers and it's good for about 20-30mA max
    Last edited by Skepticist; 10-02-19 at 07:36 PM.

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    Quote Originally Posted by Skepticist View Post
    The 5V supply could supply barely enough power for the PIC so just a modest overload would drop it to 0 or too low for the PIC to start up (<3V)
    Ran the numbers and it's good for about 20-30mA max
    Something overloading or shorting a GPIO pin set as output could drop that voltage as they can sink/source 25mA but probably not to zero volt.

    Otherwise check the electro cap C103 and although unlikely C104, both need to soldered out to confirm the short is from the PIC.


    If the PIC is really fried you could just replace the triac with a switch and a second switch to insert a suitable diode in series so the motor runs on a half wave.
    That will give you two speeds, LOL.
    Last edited by nomeat; 10-02-19 at 10:04 PM.
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    This is all getting a bit confusing guys
    "Half waves, tacho pulses, sink source,,,,".

    I measured the red connection unplugged. When plugged in there are no DC voltages on anything there.
    Red to Green was OL VDC - Red to Yellow was OL VDC - Black to Red -4.6VDC Black to Yellow -4.6VDC

    I measured the resistance across VSS-VDD and it was 260KΩ (fluctuating a lot), power off. But when I checked with power on, and I'm sure it read 1.7MΩ!!?? and it showed 47KΩ (slight fluctuation). Tested again and it's reading 47KΩ ish.

    So should I take out and test C103 and C104 (which is tiny!!), I don't' have any SMD stuff - but I can have a go

    How do I test if this PIC is 'shorted'.

    I can go to my local repair place pretty good (Resch Electronics), and see if they can order me a PIC in?
    Or am I getting in too deep for my own good?

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    Strange as it might sound, the mains active is the +5V DC (Vdd) and the yellow wire is 0 volts (Vss)

    That's why you find 240V AC all over the place and they'd design it this way for economic reasons like size, weight, cost savings due to no transformers, opto couplers etc. It also makes the circuit extremely hazardous to work on live, earth connected to the metal frame and the entire circuit 'floating' at mains potential. That's why I suggest troubleshooting around the PIC using an external 5V supply - it's way safer and less chance of blowing up your expensive test instruments.

    The PIC has to be programmed with the correct code and not much chance Kenwood is going to make their trade secrets public or even hand out the hex file. I've seen replacement complete PCBs online but the high asking prices make buying a new appliance a better option unfortunately.
    Last edited by Skepticist; 11-02-19 at 10:09 AM.

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    As for an external 5V supply, I'd put some impedance like a 22ohm 5W resistor in series to protect the supply if there is a major short cct so there's not too much of a melt-down. That would supply up to near 100mA max while maintaining the voltage on the PIC above 3V.

    That way you could determine whether the voltage collapse is due to overload on the PIC board or reduced capacity choking the power supply circuit on the other PCB.

    Isn't this fun - well maybe not for all

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    Ok.
    I went to the local repairer and they can't sell (get from Kenwood), a standalone PIC. But a whole replacement board (with PIC), is a lot cheaper than I thought.

    Now for the real hard question....

    A replacement "Main PCB" board is $48..!!
    And a replacement "Speed Controller" board is $35..!!

    The Main PCB is the Rear one and the Speed Controller is where the PIC is.

    So which board do you think I need to replace guys, considering that (from what I think you are telling me), is that the Main PCB should be creating the 5VDC, but the PIC may have gone. But the Main PCB may have blown the PIC,,, oh boy!!!!

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    From the test figures so far, my bet is on the fault being in the PIC board but I'd be doing some more testing to be sure.
    IE the 5V supply is fine until the PIC board is connected so the external 5V supply testing would verify that there is an overload situation
    Those prices are not too bad compared to what I saw on foreign sites

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    dont buy it yet we are having too much fun perhaps we should take a poll on which one after we have exhausted all thoughts but the my brain is fvckt any way lol
    . Please treat people as you would like to be treated yourself.

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    You could test the 5V supply under load but there's a bit of danger there (everything live at mains voltage)
    Unplug the 3 wire (red/yellow/green) connector
    Solder a LED with a 150ohm resistor in series between active and the yellow wire's tab (anode to Active) taking extreme care to insulate all parts from the earthed metal case
    Connect to the mains
    that'll be a 20mA load roughly so if the LED lights up then there are no worries about the 5V supply being OK

    Oh and wear safety glasses and keep a safe distance etc etc
    Last edited by Skepticist; 11-02-19 at 03:50 PM. Reason: grammar malfunction

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    Alright, I get the message.
    Glad everyone's enjoying the show H!

    But you know what, Austech has been a great place to learn and for people like me with the guidance from the more experienced people, it's been great.
    So if everyone learns something from everyone's experience, it's a good thing.

    I'll have a go tomorrow at doing this 5v testing thing. It's my birthday bash tonight. Ribs galore I hope

    I only have one PS that does 0-30vdc and I don't want to blow it up!!!
    Just crazy that you're inferring that the 240VAC is floating on around everything due to cost savings...

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    see if you can find a old carpenter they usually have an old isolating transformer laying around so you wont be laying around shaking the used to use them for their power tools etc and are the safest to use as it makes the ac earth free and zap free for you . i use one always much better than a rcd cheers don
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    Knocked up this quick schematic of the power supply for interested parties:


    (Couldn't read all the values from the posted pics)

    Correction: R2 is 51ohm not 5.1ohm
    Last edited by Skepticist; 11-02-19 at 06:32 PM. Reason: errata

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    The test with the external 5V supply is with no AC connection at all (plug pulled out so board is dead) and the power supply board CN206 plug pulled out
    The PIC doesn't care where the 5V comes from as long as the polarity is correct and will oscillate if it's ok.

    Nomeat mentioned a single port on the PIC possibly failed causing the overload and yes I've had that happen myself - new PIC is the only remedy for that unless the short is external to the chip (EG tracking between pads)

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    For a 5V test supply just slaughter a USB supply from an old phone/device, which you surely must have lying around. Find a weak one with 500mA or less.
    Chop off the USB plug and you see usually 4 wires. Red and black might sound obvious but not always. So test first with a multimeter where the 5V is.
    Just test the PIC with the resistor Skepticist mentioned, do NOT connect mains. You can pinch the bridge next to C103 to isolate it. If you have desoldering wick you might be able to isolate the plus pin of the PIC and hold the +5V on that.

    Only consider replacing the board with the PIC. The other one is most likely fine and if not the parts are easy to get.
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    I have everything ready for connecting 5VDC.
    Before I do, I assume that Red PIN5 VSS is positive and PIN14 VDD is Negative?

    So when I have 5VDC going in, what pins am I looking to check or is this intended to 'wake' it up

    And would you believe it! In my faffing around I came across that bloody big rubber belt and I can't remember where it goes or even if it's part of the mixer (I've got so much crap on me bench...)


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    HB & hope your hangover isn't too rough

    The PIC connections are the other way round IE positive to pin14 (Vdd), negative to pin5 (Vss) and don't forget the series resistor.

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    Don't have a 22Ω 5W, but Jaycar have this: Will it do (wire wound?)

    22 Ohm 5 Watt Wire Wound Resistor
    CAT.NO: RR3258

    I put it in series on the POS side, or it doesn't matter?

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