Repairing a Yanmar 3-Way Engine Buzzer Alarm (one buzzer alarm for temp, oil, alt)

This post describes a past project performed in 2010.  The vessel at the time was our previous Johanna Rose, a 1979 C&C 29-mk1,  which had a Yanmar 2QM15 auxiliary engine. 


I originally posted the text below on the CnC-list.com mail listserver in Dec 2011.  I have updated the component prices and added some accompanying photos

"I replaced/repaired the Yanmar engine buzzer alarm a few years ago at a cost under $30.   It turns out to be pretty easy to replace the guts of the buzzer with a new Sonalert buzzer.  This keeps the buzzer and wiring harness looking like an old unit but working like new.   It was an easy enough task that I later fixed an similar Yanmar alarm for buddy.  I took some pictures of the second process, and I have been meaning to write it up, but I have been forgetful.  I'll summarize my procedure below.

First let me explain how the original buzzer works.   There are 5 wires leading from the buzzer wire socket to the buzzer unit.  The red is 12V which becomes powered when the ignition key is turned to the on position.   There are three blue wires which go to water temperature, oil pressure, and alternator sensors.  There is a yellow wire which is not used at all.   When the ignition key is on, the buzzer is supplied +12V.  When a sensor trips it provides the ground for the circuit allowing the buzzer to sound.   For example, one of the blue wires merges with the ground wire for an alarm panel light bulb and then connects directly to the hot water temperature sensor on the engine block.  When the sensor over heats, it trips and provides a direct ground of the buzzer and its alarm light to the engine block.  Buzzer sounds and light goes on."

Components:

•  Replacement buzzer:  Mallory Sonalert part # SC616NL
• costs about $27 (2019 Digi-Key # 458-1026-ND)
• I spoke with an engineer at Mallory who claims this sealed buzzer is commonly used for marine applications
• 3 rectifier diodes  1N40007 
• cost: Quantity of 10 cost $1.09 (2019 Digi-Key # N4007-TPMSCT-ND)
• Note: current flows only one way in a diode.  The diodes are used to isolate the grounds so that only the corresponding alarm light turns on.

Procedure:

[1] Remove old buzzer from vessel

Remove the old buzzer from the yanmar panel.  The body of the buzzer screws on to the face guard sandwiching the panel plate. Just grab the buzzer body and turn to loosen.   If it is too tight, try one of the rubber strap oil filter removers to get better leverage.

[2] Remove old buzzer guts and enlarge inside opening

On back of the buzzer remove the sticky black sealant to get access to where the old buzzer wires enter the buzzer circuit board. Now cut or break the wires off at the old circuit board in the buzzer.  NOTE:   the wiring harness first goes through a rubber grommet then to the inside circuit board.   Use a screw driver and hammer to break up the old internal circuit board and remove the with needle-nose pliers.   The metal cross backing which also hold the rubber grommet is pressed into the back of the alarm.  Pry/pull it off of the back of the buzzer housing.   Now remove the old buzzer internals by using a Dremel to cut it out from the front side of the buzzer.   The hole left from cutting out the old buzzer internals is about the same size as the treads for the new buzzer.  Use the Dremel to sand and clean up inside diameter so that the new buzzer fits.

[3] Install new buzzer

Insert the new buzzer from back side of the old buzzer housing and screw the cap nut on the front side.  Use a little silicone sealant to seal the frontside threads and cap nut.

[4] Solder buzzer to old buzzer wiring harness.

Solder the silver end of a diodes
to each blue wire.  Twist the other
ends of the three diodes together and
solder to the new black buzzer wire.

The new buzzer has two wires: red and black.   Connect the red wires. You will need to solder and shrink tube the old and new red wires together. Prior to heating the shrink tube, I applied some liquid electrical tape over the soldering, let dry, then heated the shrink tube(or one could use adhesive lined heat shrink tube).  The new black wire is connected to the three blue wires via the diodes.  Look at the diode. It will have a black body with a silver end.  Solder the silver end of a diodes to each blue wire.  Twist the other ends of the three diodes together and solder to the new black buzzer wire.  Now use liquid tape and shrink tube (you should slip on the shrink tubes before soldering).  I also used a larger heat shrink tube over all of the wires as final step.

[Sorry, I do not have photos of the soldering process]

[5] Final clean up before reinstall buzzer back in panel.

Add a final touch of new-ness to the repair by renewing any sunlight discoloration of the black plastic cover cap.  There are many ways to do this, such as cleaning, polishing, and waxing (like one would do to renew a headlight lens), or scrub, clean, and spray paint.   For this project I recommend spray painting with black Krylon  Fusion.