Need failed Speed sensors

Rich,

Do you have a part number?

Mike

 

There are the early ones and the late model ones. Which one are you working on?

 

His might be the third (later) "electronic" type 116987? (since his Profile shows a euro 308QV)

 

Rich, i can post the circuit diagram and scope shots, let me now what you need (i am also working on a replacement based on modern parts). Basically there are three different types which are based on the same circuit design, but have different mechanics/body types.

 

I've pulled one apart - THERE IS A TRAP! Let me know if don't know how to do it.

 

Rich,

below is the circuit diagram of the previous speedo sensor 124146, which is similar to the earlier 106324 and later 116987 sensor type. I've also added an early draft component diagram of your 116987 sensor below as well as a scope shot of a sample sensor output signal at 40 km/h.

Had some discussions with Ferraridoc about a new design some time ago and Patrick was so nice to donate his broken 116987 for further analysis (thanks!), will finish the 116987 diagram as soon as it has arrived.

The two earlier sensors are based on a VR sensor coil with a center tap (thus the three wires), Q2 is switched based on the coil output signal to create a pulse wave type output signal (see scope shot).

My plan was to create a new circuit design based on an automotive grade hall sensor with a permanent magnet installed at the south side, and then add another switching transistor and input filter circuit to adapt to the speedo input requirements. I think that the circuit redesign is relatively simple but am not sure how fabricate the sensor body (mechanics are not my forte).

You are not stepping on any toes, happy to share the work and/or giving support.

Best,
Adrian
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Rich, excellent! Working in a Navy research lab sounds like a fantastic job to me, BTW

You should be able to easily disassemble the broken sensor you have it by uncrimping the top edge of the brass body, then gently pushing the internals out from the bottom side. The internals consist of a white plastic cover (wire holder), the circuit board and the black/brown coil pickup at the end of the circuit (visible through the opening at the bottom).

Patrick has experience in this and can explain in detail.

If you are able to fabricate the threaded brass body then i could try to design a PCB with the hall sensor at the end which can be potted into the body with PU or epoxy, so no additional cover or crimping would be required. Just a thought.

 

And just now the postman brought Patricks donated sensor (thanks!), great timing
Updated 116987 component diagram attached below.
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Hi Rich, Adrian

Looks like you're getting it sorted. As you can see in Adrian's photo, I broke the end off the PCB trying to prise it out, before I discovered it needs to be pressed out from the inside.

Rich has maintained the integrity of the board! I was going to source a Hall Effect sensor (needs to be high temp) online and either machine an adaptor to fit the old housing, or just epoxy the whole thing in, but I'm just too busy and passed the ball.

Let me know how it goes - I think with you two going at it, we should get a good alternative to a NLA sensor that is used across a lot of Ferrari models.

Patrick

 

Hey Rich, I think I passed you on Thomas Dr on the 4th this past summer. I have a bay home in Lynn Haven and we are down in PCB a lot.

 

Hey Rich, I think I passed you on 98 in early August this past Summer. I have a beach condo on Thomas Drive and we are down in PCB every Summer.

Plus I've already verified it wasn't TatCat. Looks like we need a gathering!

 

Adrian, I always enjoy your posts Thanks

I am curious about the one transistor that has no connection to the collector. I know they have always been that way but I can not understand why. Do you know what is up with that?

Thanks again ,
Paul

 

We were leaving Bay Point heading out to see a friend down on Rosemary Beach when you passed me. I knew I would eventually find you here

(and after 40 plus years I still love Anderson's.)

 

We're very close. Our place is at The Dunes of Panama, across the street from Mr. Surfs and Fins. I should invest in Fins my wife eats there so much.

Back on topic: I'd be interested in a sensor if you get them made, assuming it fits a 328....

 

You can reuse the threaded body and also fix the internals (see also http://www.ferrarichat.com/forum/308-328/416720-308-early-speedo-drive-sensor-repair.html) but not everyone has the skills and it is probably more convenient to create a modern replacement. If you think fabricating the brass threaded body is feasible then i could do a prototype circuit board for testing.

The transistor without the collector connection is behaving like a diode, except that it has a lower voltage drop than a standard diode. Nowadays you probably would use a schottky diode instead of a half transistor.

 

Thanks! I am looking at this circuit because I am trying to build something similar to get the speed signal into the Arduino for the electric MG. I have a magnetic hall sensor and I need to trigger a digital pin. I think with your layout I have a good place to start. Thanks again

 

FYI, the earlier sensors usually fail because oil enters the body through the axle seal and then damages the 1.5nF capacitor. Less common defects include a failure of the transistor or a wire break for the coil wiring where it enters the PCB. I have one sensor in for repair from John, where i think that the magnet itself failed due to age.

The later type is pretty well sealed, so the more common defects are failures of the transistors or a coil wire break. (Patrick, on your sensor the coil windings had developed a defect, the components were in pretty good shape).

From my experience this only works if you ship ready to install products, as automotive dealers and workshops quite often don't have the experience to produce or rebuild electronic components, but rather outsource this to specialized suppliers.

Best,
Adrian

 

That is quite straightforward A hall sensor usually has a Vs, GND and Out pin. Wire "Vs" to the Arduino's "5V" terminal, "GND" to GND and "Out" to one of the digital input ports. Configure the input port to activate a pull-up (PORTx |= (1<<Pxn)) or solder a 10K resistor as pull-up to Vs and Out.

 

Did a first draft design of a new hall sensor based circuit board. This board fits into the original brass housing, and will be potted in place with epoxy or PU. No further parts are required except the wire trunk with connector.
I'll build up a prototype next, if that works out as expected we need to think about how to produce the brass body.
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