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  1. #1
    Join Date
    May 2014
    Posts
    32

    Default MD2B rpm sending unit

    Hi All,

    My RPM gauge is not working, and I'm suspecting the sending unit is defective.
    I believe this unit concerns a Hall Effect sensor.
    Does anyone know how I can test this sending unit, ie. how much resistance (Ohm) should be measured if okay ?
    Also, how much voltage should I normally read on the two connecting wires ?

    Also, one of the blade connectors has now broken off (unit was already defective beforehand):
    can this be restored/soldered by a workshop ??

    THANKS,
    V.
    Myra 21 - 1973 - MD2B MS

  2. #2
    Join Date
    Nov 2001
    Location
    Me: Johannesburg South Africa Yacht: Durban East Coast Africa
    Posts
    5,452

    Default Re: MD2B rpm sending unit

    Quote Originally Posted by Vronsky View Post
    Hi All,

    My RPM gauge is not working, and I'm suspecting the sending unit is defective.
    I believe this unit concerns a Hall Effect sensor.
    Does anyone know how I can test this sending unit, ie. how much resistance (Ohm) should be measured if okay ?
    Also, how much voltage should I normally read on the two connecting wires ?

    Also, one of the blade connectors has now broken off (unit was already defective beforehand):
    can this be restored/soldered by a workshop ??

    THANKS,
    V.
    The RPM sender unit is most likely be a VDO unit

    The various units are listed here

    https://www.vdo-instruments.com/sens...l-sensors.html

    It will be easier to to identify is you can post a picture

    It looks like item 21 on this breakdown draving

    https://www.marinepartseurope.com/en...-30-13792.aspx
    Last edited by Rogershaw; 14-09-17 at 08:47.
    Life is too short not to have a sea view
    Distantshaws tinyurl.com/ybrn7prn

  3. #3
    Join Date
    May 2014
    Posts
    32

    Default Re: MD2B rpm sending unit

    Here''s a pic of the unit >>

    http://www.boatpartsandspares.co.uk/...sor-2356-p.asp


    I understand these units are out-of-production.
    Am considering using a different model together with a thread-adapter, but I need to know if it's an inductive sensor, or Hall Effect (incl. magnet on handstart shaft gear)
    Last edited by Vronsky; 14-09-17 at 09:38.
    Myra 21 - 1973 - MD2B MS

  4. #4
    Join Date
    Nov 2001
    Location
    Me: Johannesburg South Africa Yacht: Durban East Coast Africa
    Posts
    5,452

    Default Re: MD2B rpm sending unit

    Your picture won't display as photobucket has turned off 3rd party hosting.
    Life is too short not to have a sea view
    Distantshaws tinyurl.com/ybrn7prn

  5. #5
    Join Date
    Jun 2001
    Location
    Scotland
    Posts
    6,135

    Default Re: MD2B rpm sending unit

    Quote Originally Posted by Rogershaw View Post
    The RPM sender unit is most likely be a VDO unit

    The various units are listed here

    https://www.vdo-instruments.com/sens...l-sensors.html

    It will be easier to to identify is you can post a picture

    It looks like item 21 on this breakdown draving

    https://www.marinepartseurope.com/en...-30-13792.aspx
    I believe that the Volvo unit is inductive and senses the timing gear teeth . The items at the bottom of this page seem to match especially. P/N 340-804-007-002A. 28.5 mm thread length 18 mm .

    I get a reading of around 1500 ohms one from my md2b. These things certainly fail from time to time and cost around 70 from Volvo.
    Eastern Scotland and beyond.

  6. #6
    Join Date
    May 2014
    Posts
    32

    Default Re: MD2B rpm sending unit

    Thanks, I'll check your readings with my unit, but are you sure this is an inductive sensor?
    Inductive sensors usually have 3-wires, while 2-wire sensors seem to be Permanent Magnet Generators >>
    https://axleaddict.com/auto-repair/D...is-and-Testing

    Quote Originally Posted by Bilgediver View Post
    I believe that the Volvo unit is inductive and senses the timing gear teeth . The items at the bottom of this page seem to match especially. P/N 340-804-007-002A. 28.5 mm thread length 18 mm .

    I get a reading of around 1500 ohms one from my md2b. These things certainly fail from time to time and cost around 70 from Volvo.
    Myra 21 - 1973 - MD2B MS

  7. #7
    Join Date
    Oct 2007
    Location
    Poole
    Posts
    1,586

    Default Re: MD2B rpm sending unit

    You can get a new rev counter for 50 and connect it to the W terminal on your alternator if you have one, as most seem to.

  8. #8
    Join Date
    May 2014
    Posts
    32

    Default Re: MD2B rpm sending unit

    Thanks! Yes there are alternatives, even much cheaper than the W-terminal solution, but I first like to try to restore the original thing (in a cost-reasonable way)

    Cheers,
    V.
    Myra 21 - 1973 - MD2B MS

  9. #9
    Join Date
    Mar 2005
    Posts
    4

    Default Re: MD2B rpm sending unit

    Hi,

    This is of a Swedish forum, a guy measured his sensor on a MD17 (which has the exact same sensor).
    I am having this issue with the sensor on my 2002, so hopefully you solution can help me too.

    Resistance: 1.06 kohm. (1060 ohm) when disconnected.
    DC with ignition on (position 1): 0.26 V
    Idle (800 rpm): 0.22 V DC and 0.97 V AC.
    2000 rpm: 0.22V DC and 1.66 V AC

    Please post your measurements if you can.
    I did not get anywhere near these figures with mine, disconnected resistance is infinite so I believe it is dead..

    Cheers,

    Otto

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