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Speedo died. Which sensor is it?

Discussion in '348/355' started by WATSON, May 26, 2019.

  1. WATSON

    WATSON F1 World Champ
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    Green/white on the speedo connection has 12 volts with ignition on.
     
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  3. WATSON

    WATSON F1 World Champ
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    Talk to me about 30012. Where is that connector?
     
  4. Qavion

    Qavion F1 Rookie

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    ah.... I didn't realise that the new ones at Eurospares were "New To Order" (up to the factory to provide one). They have 3 used ones, but I don't know if they are any good.

    Strange. That doesn't make sense at all. Anyway, if the speedo doesn't work, the problem is either the speedo, power to the speedo or wiring to the sensor.

    I meant the speedo sensor, but it won't hurt to check voltage going to the speedo. Anyway, on the plug for the speedo itself, power comes in on the green/white wire. Unfortunately, I don't know where the splices are for input power and output signals. I've tried tracking wiring in that area for other reasons and the wiring bundles are too thick to follow individual wires.
     
  5. Qavion

    Qavion F1 Rookie

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    Not a connector, but a splice. This will be hidden in a harness somewhere. Impossible to find.

    To check the sensor power wiring (green/white wire), just check the voltage at the sensor (or plug 41019 near the strut) with the battery/ignition on.

    To check the sensor signal wiring (red/white wire) you'll have to use an ohmmeter between the sensor and the speedo.
     
  6. Qavion

    Qavion F1 Rookie

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    ... with the car's battery off.

    I'm just wondering if there are cheap signal generators which can reproduce the speedo signal (at various speeds) which you can inject into the wiring. Is Miro following this thread? :)
     
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  8. m.stojanovic

    m.stojanovic Formula 3
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    There are many signal generators on Ebay, cheap ones are $3 to $10. They usually have choice of square, sine and triangular wave form signals, variable from 1 Hz to thousands of Hz.

    On the other hand, the speed sensor is probably a Hall Effect transistor which can be tested in the same way as the cam sensor - by bringing a steel object to the sensor "face" and checking the voltage change on the sensor's output wire.
     
  9. RossoCorsaItaly

    RossoCorsaItaly F1 Rookie
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    I had a similar issue back in 2008 on my old 355F1 that made my speedo not work and didn't let my 355 shift past 2nd, was the result of a simple blown fuse, which kept blowing due to one of the cables from the fusebox being loose.

    If you want to get past 2nd gear, just go to your desired speed via 2nd gear, shift it into neutral and then downshift and it'll pick gears 3-6 depending on your speed. You can still downshift to reach your desired gear, just can't upshift from what I recall.
     
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  10. Qavion

    Qavion F1 Rookie

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    #33 Qavion, Jun 1, 2019
    Last edited: Jun 1, 2019
    I was thinking more of a signal generator to mimic a reliable signal from the speed sensor over a range of speeds, to see if the wiring and speedo are ok. I could plug it into the connector near the suspension strut. I've ordered a $10 signal generator which operates over a range of supply voltages, but I'm not sure if the output will be suitable. Will it produce a square wave which changes polarity? Doesn't the hall type sensor provide a positive voltage which increases/decreases in amplitude?

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    Kevin, can you recall which fuse it was (and if any other instruments were affected)?
     
  11. Qavion

    Qavion F1 Rookie

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    https://www.ebay.com/itm/183780308442

    I think I just bought something totally unsuitable. It only has a 5 volt output :rolleyes:
     
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  13. WATSON

    WATSON F1 World Champ
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    #35 WATSON, Jun 1, 2019
    Last edited: Jun 1, 2019
    Here is what I know:

    1. The suspension light is back on and was gone only because I had battery knob off for a few days.
    2. The speedo sensor on the gearbox is new and connected correctly.
    3. I have 12 volts at the green/white wire on the back of the speedo with the ignition on.
    4. The lights on the speedo work so the black ground wire is OK and I assume the yellow /red wire to power them is working.
    5. The suspension waits it's usual three starts before the light comes on so I will assume the yellow / white wire form the speedo to the suspension ECU is OK seeing as the speedo dial does not move.
    6. I checked and verified the "A/C - Instruments" fuse in the foot well fuse box is OK.

    So, how can I check the "signal in" (red / white) wire?
    I have the car up on the lift with the wheels free so I can "drive it" in place to check the speedo....

    I'll try and ohm out that signal wire today today I guess.
     
  14. m.stojanovic

    m.stojanovic Formula 3
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    The Hall Effect sensor provides just on-off pulses the frequency of which is proportional to the speed of the reluctor (the speed of the car). The amplitude does not change. It should be zero-12V-zero-12V etc. but it may also be zero-5V-zero-5V etc., depending on how Ferrari designed the receiving circuitry. So, the gadget you bought may still be usable. For a simple test, you don't really need to vary the frequency of the signal generator - just find a frequency (say about 50 Hz) that will move the needle of the speedometer to some value and it will confirm that the speedometer circuitry is good.

    As for the choices that the signal generator you bought has, in the case of square wave, you can vary the frequency and probably also the duty cycle (how long "on" and how long "off" within one cycle). The amplitude appears to be fixed at 5V. As for the polarity, you will have to see if there is a choice for the "on" phase to be +5V or -5V. The "off" phase is, of course, zero volts.

    To match the duty cycle with that of the speedo sensor/reluctor, you will have to see what the circumferential lengths of the reluctor's "off" and "on" segments are. Then calculate the ratio of the length of the "on" segment to the combined length of one "on" and one "off" segments. If the length of "on" is, say, 30% of the length of "on" and "off" combined, the square wave has 30% duty cycle. However, I don't think the duty cycle is critical if you just want to establish whether the speedometer circuitry is good or bad. You can test with a 50% duty cycle and a frequency that is within the range - the needle will move, and sit steady at certain speed. Than you can vary the frequency up and down to verify that the speedometer needle is following the changes.
     
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  15. Qavion

    Qavion F1 Rookie

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    If the continuity (ohm) test between speedo and the sensor is ok and there is power going to the sensor, then that really only leaves the speedo and the gearbox reluctor as faults. You can only (properly) check the reluctor by monitoring the "square wave" output signal from the speedo sensor on the red/white wire (with the wheels turning) with an oscilloscope. I bought myself a $100 rechargeable pocket digital oscilloscope, but I can't say I've seen any return on my investment.

    https://www.amazon.com/d/Lab-Oscilloscopes/SainSmart-Portable-Pocket-sized-Handheld-Oscilloscope/B01N6PI0FG

    If you want to skip this step and assume the speedo is broken, I guess you have the option of having it repaired or finding a good used one. A used one will leave you with the problem of matching the mileage. Unless you're an electronics whizz, I guess you'll have to hand it over to the experts.
     
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  16. Qavion

    Qavion F1 Rookie

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    Thanks, Miro. I wasn't sure if the workshop manual graph was showing a drop from 12 volts to 6 volts. Those oscilloscope crosshairs are confusing. Still, a drop to zero is an amplitude change of sorts :D
     
  17. m.stojanovic

    m.stojanovic Formula 3
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    I have not had a look at the graph. Does it show the voltage at "on"? Otherwise, if the speedo sensor circuitry (powered by 12V) is such that it sends 5V pulses, there will be no drop 12 to 5 shown on the graph, just zero and 5V.

    The amplitude of a wave is the difference between zero and the max. voltage to which the wave goes. In the case of the square wave, it is the difference between zero and whatever the voltage is in the "on" state. The voltage changing from zero to X volts, back to zero, to X volts etc. is not a change of amplitude (the amplitude is still X volts minus zero, X volts actually) but oscillation.
     
  18. WATSON

    WATSON F1 World Champ
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    Well, well, well, No ohm on the signal wire from the sender to the dash.

    Guess what I am doing today???....all day...if I am lucky to get this done in one day....

    Ugh
     
  19. Qavion

    Qavion F1 Rookie

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    eeek... Well, that's some progress in the right direction (and may be a cheap fix)

    Break up the circuit into segments. You have the connector near the strut (41019) and the white connector forward of the centre console (adjacent to the passenger footwell/relay panel) 41024.

    I'm not familiar with the F1 car, so there may be 3 white connectors in the forward console area instead of the usual 2. Don't know if you have removed the carpeted "saddle" in that area, but there are a number of hidden screws. It may be best to drop the passenger footrest and have a look from the side (to see if there is anything obvious. Photos appreciated )))

    Did you use a long piece of wire when doing the ohm checks or did you use local grounds at both ends?
     
  20. WATSON

    WATSON F1 World Champ
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    Ooooops. Just checked and I did it backwards. The signal wire does ohm out.

    After checking through the connections and working my way back I found my error.

    I was checking off the green / white ( + ) wire side of the sensor. Of course it did not ohm out on the red / white one on the speedo connection.

    The red / white wire (which connects to an orange on my new sensor....green on my old one) ohms straight through.

    So. Speedo our gearbox disaster.
    I'll go with the speedo first. :)
     
  21. Qavion

    Qavion F1 Rookie

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    #43 Qavion, Jun 1, 2019
    Last edited: Jun 1, 2019
    Interesting. I have bright green as the power wire (on the sensor) and a muddy looking green as the signal wire on the sensor on my diagram. I'll add "orange" as a colour variation footnote.

    Latest Instrument Diagram (5.2)
     
  22. WATSON

    WATSON F1 World Champ
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    My car came with a box of parts and in there were two other speedo sensors.

    The ones in that box, and the one I installed 8 years ago that I just pulled out, all have a dull/dark green (+) and a black (well maybe an ugly dark brown) ( - ).
    These all have a marking on the tan plastic in the connector end identifying the (+) and (-) sides.

    The one I just bought from Ricambi has a black (-) but an orange (+) side.
    It also is without any markings on the plastic casing...and that casing is now black.
     
  23. WATSON

    WATSON F1 World Champ
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    I just did a test on the Type 2 sensor I took out that I am pretty certain is OK.

    http://www.dinoplex.org/instruments/vegliaspeedosensor/

    With the resistor in place and my meter set at 20 DCMa (because that's the only option on this meter) I get these readings:

    1.00 with nothing in front of the sensor
    0.50 with a wrench in front of it.

    Thoughts???

    One of the really old ones just tested as follows:
    0.30 with nothing
    0.28 with a wrench in front.
     
  24. m.stojanovic

    m.stojanovic Formula 3
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    You should set your multimeter at DC Volts, not milliamperes. The milliampere setting is just shorting the signal to the ground.
     
  25. WATSON

    WATSON F1 World Champ
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    OK. I'll try that next. I followed this:
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  26. WATSON

    WATSON F1 World Champ
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    Sooooooo.

    Now it works.

    I took the speedo apart and pulled the little circuit board out and cleaned up the connections and checked each one.
    Flipped the board over and touched up any solder joints that looked even remotely "suspect" or possibly cold soldered.
    Installed it all and am waiting on conformation of my $1400 used speedo from Eurospares and figured...what the heck, everything else checks out.

    Fired it up (still on jackstands) and ran it up to 30 MPH and able get third gear now.....no suspension light.

    Gulp....no what? Trust it?
    Man I hate these kind of problems.
    At least it does not appear to be the gearbox :)
     
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  27. Ferrarium

    Ferrarium F1 Rookie
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    Pretty sure used Speedos on eBay are 400-600 fwiw may be what you need maybe not I was looking today.

    Sent from my LM-Q710(FGN) using FerrariChat.com mobile app
     
  28. WATSON

    WATSON F1 World Champ
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    Thanks. I saw those on e-bay. If mine failed....there is no way those POS will make it. :) hahaha

    Although..... I may buy one just for the small circuit board as I think that is what is failing. The rest is just mechanical gearing.
    We could just swap the circuit board and mileage stays where it should and life is good. Hummmmmm
     
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