News

308 Speedo Repair/Rebuild

Discussion in '308/328' started by alhbln, Aug 22, 2013.

  1. alhbln

    alhbln Formula 3
    Owner Consultant

    Mar 4, 2008
    1,656
    Berlin, Germany
    Full Name:
    Adrian
    #1 alhbln, Aug 22, 2013
    Last edited by a moderator: Sep 7, 2017
    308 GT4/GTB/GTS Speedos use a SAY115Y driver IC on the circuit board, which has been obsolete for a long time and is increasingly hard to source since some years. Defects of the SAY115Y usually lead to a temporarily or permanently defunct ODO and sometimes also to a dead speed pointer. RJay, gerritv, DGS, Crowndog and others created several threads about SAY115Y issues with lots of good infos.

    If both the Speedometer and the ODO are gone though there is a good chance that just the sender is broken though (have a look at this thread for how to repair speed senders: https://www.ferrarichat.com/forum/308-328/416720-308-early-speedo-drive-sensor-repair.html)

    I noticed that the last Speedo i've repaired using a NOS SAY115Y IC started to exhibit similar ODO problems after several weeks again, and Nickt's Speedo also seems to have the same ODO problems after a SAY115Y replacement. There is a good chance that the shelf lifetime of these now 30+ years old ICs could have been reached, and paying about $80-100 for a NOS SAY115Y does not seem to be an attractive option considering the chance of another ODO failure.

    A possible solution would be to design a new circuit board which does the same as the SAY115Y circuit board but relies on standard electronic components which are cheap and easy to source. Since this looked like a fun job i did a draft design of the hardware which turned out nicely and then programmed the SAY115Y logic in C as embedded firmware for a small microcontroller. The final board has the same shape and size as the original circuit board and the cost for the electronic components excluding the PCB is only around $10.

    As a nice plus the new board features an integrated calibration signal generator which allows you to calibrate your Speedo on the workbench. An integrated diagnose LED can be used to check if the Speedo sensor is still good.

    The board passed bench testing and several test drives which all looked good so far. Will do some more testing and Nickt also opted in to help with testing one of the boards. If it passes i'll publish the circuit drawings/PCB/sourcecode if anyone wants to go that way for a repair.
    Image Unavailable, Please Login
     
    Saabguy, eyeman1234 and Bo Loof like this.
  2. st@ven

    st@ven F1 Rookie

    Aug 4, 2008
    2,882
    Italy, Milan
    Full Name:
    Steven
    Very interesting!!! Could this also be used to rebuild a mls to km conversion?
     
  3. alhbln

    alhbln Formula 3
    Owner Consultant

    Mar 4, 2008
    1,656
    Berlin, Germany
    Full Name:
    Adrian
    Yes i think so, the software has a configurable parameter for the incoming pulse to ODO ratio. Changing that parameter would allow the ODO to count in km/h instead of miles.
    If the km/h dial face has different speed positions for the same km/miles speeds then a quick recalibration using the internal calibration generator would easily rectify this.
     
  4. st@ven

    st@ven F1 Rookie

    Aug 4, 2008
    2,882
    Italy, Milan
    Full Name:
    Steven
    Wonderbar!! Do you considder selling a set, i would take two instantly
     
  5. alhbln

    alhbln Formula 3
    Owner Consultant

    Mar 4, 2008
    1,656
    Berlin, Germany
    Full Name:
    Adrian
    Still in test phase but you could apply as a tester if you like. Send me your mph tach and a km/h dial and i'll do a conversion if it turns out to be feasible (don't see why it shouldn't).
     
  6. Ferraripilot

    Ferraripilot F1 World Champ
    Project Master Owner

    May 10, 2006
    16,118
    Atlanta
    Full Name:
    It's man
    Can these calibrate the speedo to read perfectly accurate too? All these units of course read too low until about 60mph and then they read too high increasing in inaccuracy the higher it goes.

    Wonderful work though Adrian.
     
  7. alhbln

    alhbln Formula 3
    Owner Consultant

    Mar 4, 2008
    1,656
    Berlin, Germany
    Full Name:
    Adrian
    Yes, thats correct, the Speedos i had in for calibration had the same behaviour as you've described. The factory Speedos are perfect at around 60 mph because that was probably the calibration point used by Veglia when they assembled the Speedos.

    That nonlinearity depends on the mechanical adjustment of the Speedo, i haven't done a mechanical calibration (e.g. adjusting the mechanism to get the output curve more linear) of the Speedo yet, but with the Tacho you can get as low as a 2-3% error rate by adjusting the small counterweights on the coil driver mechanism.
    Now that i think about this, i could modify the firmware to send increasingly less energy (pulse width) to the Speedo coil driver with rising speed to compensate for the nonlinearity of the needle mechanism. I'll have a look if that works :)
     
  8. Ferraripilot

    Ferraripilot F1 World Champ
    Project Master Owner

    May 10, 2006
    16,118
    Atlanta
    Full Name:
    It's man
    Excellent! That would be an absolutely magnificent upgrade for these things
     
  9. glenv6

    glenv6 Formula 3

    Jul 4, 2011
    1,158
    New York
    Full Name:
    Glen
    ...^^...worth the upgrade rather than waiting until the speedo died before replacing the old board!

    Thanks for putting the time in to do this work! I will build or buy a PCB.
     
  10. alhbln

    alhbln Formula 3
    Owner Consultant

    Mar 4, 2008
    1,656
    Berlin, Germany
    Full Name:
    Adrian
    #10 alhbln, Aug 23, 2013
    Last edited by a moderator: Sep 7, 2017
    Was curious and did a test run with the my calibrated Speedo/new board. Looks like the derivation of my Speedo is below 2%, that's surprising. Could be that i'm lucky and the Speedos mechanics are in top notch condition.
    To get rid off the pointer flutter at very low speeds i am sending double the amount of pulses to the needle coil driver but with half the pulse width compared to what the SAY115Y does, maybe that had a positive influence on the linearity? The small spikes in the light green line are measuring artefacts and can be ignored.
    Image Unavailable, Please Login
     
  11. Ferraripilot

    Ferraripilot F1 World Champ
    Project Master Owner

    May 10, 2006
    16,118
    Atlanta
    Full Name:
    It's man
    wow, so it's accurate now. amazing
     
  12. alhbln

    alhbln Formula 3
    Owner Consultant

    Mar 4, 2008
    1,656
    Berlin, Germany
    Full Name:
    Adrian
    On the workbench yes, while driving i usually have just a quick lock in which general direction the Speedo needle points.
    If you can read your current speed while driving you are still going not fast enough :)
     
    Saabguy likes this.
  13. Ferraripilot

    Ferraripilot F1 World Champ
    Project Master Owner

    May 10, 2006
    16,118
    Atlanta
    Full Name:
    It's man
    Haha! I have managed to GPS track on a very level and straight road exactly what my speedometer is doing at 100mph. Speedo reads exactly 9mph too high.
     
  14. alhbln

    alhbln Formula 3
    Owner Consultant

    Mar 4, 2008
    1,656
    Berlin, Germany
    Full Name:
    Adrian
    I guess that Ferrari wasn't too unhappy about that feature, at least when it added some mph to the actual speed.
     
  15. 1Evil4re

    1Evil4re Formula Junior

    Jun 24, 2012
    311
    Nashville Area
    Full Name:
    David
    #15 1Evil4re, Aug 23, 2013
    Last edited by a moderator: Sep 7, 2017
    What about those with larger diameter wheels? I am currently using 18" wheels with low profile tires. Using an Android Ap, my speed is low by about 10 mph. I am doing 70 mph when the speedo shows 60 mph. Also my speedo has obviously been repaired by one of the previous owners as the chrome bezel is all screwed up.
    Image Unavailable, Please Login
     
  16. 1Evil4re

    1Evil4re Formula Junior

    Jun 24, 2012
    311
    Nashville Area
    Full Name:
    David
    Also, I forgot to mention that my odometer rolls over at the half mile mark (the 5 tenths)instead of the "0" tenths. This isn't common is it and will this board resolve that issue?
     
  17. magnum

    magnum Formula Junior
    Silver Subscribed

    Feb 21, 2008
    864
    Barcelona, Spain
    Full Name:
    Antonio
    That's an excellent work Adrian!

    Congratulations for the nice job! Of course, it would be nice to buy one, just in case my old speedo starts malfunctioning.

    Please, warn us when it will be on sale.
     
  18. alhbln

    alhbln Formula 3
    Owner Consultant

    Mar 4, 2008
    1,656
    Berlin, Germany
    Full Name:
    Adrian
    The ODO readings for larger/nonstandard wheels could be corrected by changing a parameter in the software. The software default is currently set to Michelin XWX 205/70 tires with a rolling circle of 1958 mm. The Speedo display could also be adapted by a similar parameter change.

    Sounds like a mechanical problem due to an incorrect reassembly. Check out the numbers in your top ODO counter, they should be aligned vertically but they do not. This can happen if the small cogs at the side of each number disc are not aligned to each other when reassembling the ODO counter. A proper reassembly should fix both the half mile rollover and vertical alignment.
     
  19. alhbln

    alhbln Formula 3
    Owner Consultant

    Mar 4, 2008
    1,656
    Berlin, Germany
    Full Name:
    Adrian
    This is an open source/open hardware project, e.g. everything is free to use and you can do what you want with this. If anyone wants to produce and sell them, be my guest.
    If the testing turns out well i might do a small batch of ready to use boards for Fchat members though.
     
  20. kerrari

    kerrari F1 World Champ
    Silver Subscribed Owner

    Oct 22, 2004
    12,265
    Coolum Beach, AUSTRALIA
    Full Name:
    Karen H.
    Alhbin, I don't understand half of what you're saying but that is very cool and makes me reconsider my thought that electronic components can't be home fabricated...seems you just need the right skills.
     
  21. BigTex

    BigTex Seven Time F1 World Champ
    Rossa Subscribed Owner

    Dec 6, 2002
    70,785
    Houston, Texas
    Full Name:
    Bubba
    Totally awesome!

    I think 2 out of my 3 are broken.....I just hide behind other traffic from radar.
     
  22. Mike C

    Mike C F1 Veteran
    Owner Lifetime Rossa

    Aug 3, 2002
    6,061
    Southeast USA
    Full Name:
    Mike Charness
    What a wonderful project! Nice work.
     
  23. Jonny Law

    Jonny Law F1 Rookie
    Silver Subscribed

    May 6, 2008
    2,867
    La La Land
    Full Name:
    IT Guy
    I would be interested in being a beta tester. PM me.
     
  24. alhbln

    alhbln Formula 3
    Owner Consultant

    Mar 4, 2008
    1,656
    Berlin, Germany
    Full Name:
    Adrian
    PM sent
     
  25. Nielsk

    Nielsk Karting

    Dec 8, 2012
    179
    Central Florida
    Please make this available!
     

Share This Page