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post #1 of 10 (permalink) Old 06-14-2019, 12:37 PM Thread Starter
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Help in identifying speedo sensor

This was pulled from my GTV6 which is a euro 1985/86. Can anyone help confirm if this is the expected sensor for the model/year or that perhaps it would be more likely from a Milano? We suspect the gearbox could be one for a Milano/75 and maybe this sensor is a clue. I have a non working speedo and am trying to troubleshoot if it's the sensor or the speedo. What would be the right part number of this sensor and would it use a amplifier or not (like a Milano)?
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post #2 of 10 (permalink) Old 06-14-2019, 12:48 PM
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Pretty sure that’s the same as the Milano sender. Is there an amp box under the rear seat that it plugs into?

Tom

1963 Giulia Spider (1750 engine)
1974 GTV
1991 Spider
Former: 1987 Milano Gold
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post #3 of 10 (permalink) Old 06-14-2019, 12:50 PM
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Information on the Milano Speedometer system here: https://www.alfabb.com/bb/forums/mil...amplifier.html

Your sensor is either a late GTV6 or a Milano. They are in the same package. The GTV6 sensor has built in electronics (which was unreliable). The Milano has just a coil and it connects to an amplifier that lives under the back seat.

Using an ohmeter, test between the three pins of the connector. If it is a Milano sensor then the center pin to one of the outer pins should be a few ohms. The other outer pin is just a shield wire and is isloated from the other two.

Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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post #4 of 10 (permalink) Old 06-14-2019, 01:04 PM Thread Starter
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It's from my GTV6 and the GTV6 wiring diagram in the user manual i have does not indicate an amplifier. Kind of difficult to check if there is one under the rear seat (I'd have to get to the service garage). I've checked the three wires and all combination show open circuit, no combination that gives a hint of any resistance. Has someone actually opened one of these to check the circuit components? Looks like it could be opened from the rear by carefully removing the sealing material.
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post #5 of 10 (permalink) Old 06-14-2019, 01:24 PM Thread Starter
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I'm going spend sometime this weekend on this. The GTV6 sensor from what I understand is a self contained unit combining the pickup and electronics to provide the signaling to the speedometer. That signaling is suppose to be a square wave at the different frequencies. Amplitude is probably between 0 and 5V. So the question is to first test the sensor in the simplest way possible. Checked the three leads and none show a combination with a resistance so supposedly the sensor is likely to be bad. Next need to figure out the ground and +12V leads and power it up. Then I need to figure out what I could use to replicate the effect of just one gear tooth, I figure I don't need to have revolutions since I haven't go an oscilloscope to actual see the waveform. Maybe a coin will do just to cause a change in voltage on the signal output - that's enough to tell me it's not dead altogether. This I can do without having to open it up. If there is a voltage change then there's more of probability the sensor is good, and it this that bad news is that I have to focus on the speedometer itself. Sounds like a plan?
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post #6 of 10 (permalink) Old 06-14-2019, 04:30 PM
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It sounds like you have an original sensor. If it works it may be the only one in captivity. The solution is a Milano sensor and amplifier.
Easy to see if there is one under the seat - remove the cushion - a 1 minute job.

Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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post #7 of 10 (permalink) Old 06-16-2019, 09:44 AM Thread Starter
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I made some more progress and a whole lot of research for any little detail I could find.

The sensor should be a Jaeger 3-wire non-amplified P/N 60526262. If I can get to the service garage where the car is I can pull the rear seat and see if there is an amp once and for all, but I'm quite sure no 99%. Why? I also have the speedo pulled from the car and it has the 6-wire connector plus the additional green wire separately. This is info from a post of Alfisto Steve who has a GTV6 speedo p/n 60701830 with exactly this characteristic. I have a different p/n since it is a kph speedo.

None of the wiring schematics, including that from the delivered car user manual, show wiring of such speedo and 3-wire sensor. It has only a speedo with 6 wire connector and a 2 wire sensor (where the wires are pink and white-red).

The Jaeger wires are black, grey, pink/black. The speedo internal wirings are red, yellow, black , and green. What I think is:

black - ground
red - +12V
green - signal from sensor
yellow - not sure

I don't have an oscilloscope on my bench, but if I wire the Jaeger as follows:

black - ground
grey - +12V
pink/black - assume signal

and I measure across grey and pink/black or +12 and the assumed signal, I can see a voltage variation when moving a metallic object near the hall sensor. That tells me at least that the sensor is not dead, whether it is performing to spec will have to wait for an oscilloscope.

I partially disassembled the speedo to see if there any macro issue. The only one I found was the the partial odometer was somewhat stuck, I couldn't reset it with the front button (felt like a worm gear problem) but I could reset with a plier and that may have loosened it up. This have could have been the root cause the speed to stop working....a mechanical issue. The circuit board looks fine visually, but would like to do other testing. Unfortunately I have yet to figure out exactly what the yellow lead is suppose to be. On the wiring diagram for a speedo without the green lead, the yellow lead on the connector is labeled as "1" whereas red is "+" so it would still seem to be sensor signal.

The plan is to see the sensor via oscilloscope and test the speedo with a signal generator, probably square wave once I understand the amplitude the sensor provides. The various markings on the speedo tells me the calibration frequency.
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post #8 of 10 (permalink) Old 06-16-2019, 10:24 AM Thread Starter
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oops here are the pics
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post #9 of 10 (permalink) Old 06-16-2019, 01:15 PM
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If it has an amplifier module then a basic test is to put the scope on pin 7 of the chip, which goes to the sender and you should see a sine wave of about 200 KHz. If not then either a bad sender or bad chip. The sender is an inductance of about 0.2 mH which changes to 0,25 mH when it "sees" a spline on the tranny shaft. That causes the oscillator frequency to shift by about 20 KHz. The chip turns the frequency shifts into a square wave that is the frequency of the shifts.

When I am troubleshooting one that is in the car I get the rear wheels off the ground. start the car and put it in 5th gear which is about 20 mph at idle. I then check the output signal from the amp with an oscilloscope.

I posted the frequency/rpm relationship in the thread that I linked. Milano and late GTV6 speedometers are calibrated for a higher frequency signal than early GTV6's.

Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke

Last edited by alfaparticle; 06-16-2019 at 01:19 PM.
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post #10 of 10 (permalink) Old 06-17-2019, 11:37 AM
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I acquired a speedometer sensor recently that I assumed was for a Milano for use with the "amplifier" box. I just took a look at it and it is for a late GTV6 and it is working. The wires are:
Pink - 12 volts
Black - GND
Grey - signal out - 12 volt square wave.

Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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