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308 Speedo Repair/Rebuild

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

  1. alhbln

    alhbln Formula 3
    Owner Consultant

    Mar 4, 2008
    1,660
    Berlin, Germany
    Full Name:
    Adrian
    The type number 61.XXX is sufficient to identify the board, it is a Type 2 speedo.

    I have finished the Type 2 circuit board but did not find a good solution for the calibration process yet. The factory process for the type 2/3 Speedo was to send a specific speed signal to the Speedo and then install the Speedo needle in the correct position with a machine. Calibration on my PCB does the same, it creates a predefined speed signal but you would need a special tool or trained hands to properly install the needle then.
     
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  2. 4valves

    4valves Rookie

    Aug 29, 2012
    9
    Do you think that will be always in this way or will be possible to find different solution? Other solution could be to send you a speedo ( I think you are in Germany correct ) and you change card and set it ? Do you have additional solutions?
    Is it possible to repair my card, I mean the chip installed is available or like SAY 115 parts?
    Thanks again
     
  3. alhbln

    alhbln Formula 3
    Owner Consultant

    Mar 4, 2008
    1,660
    Berlin, Germany
    Full Name:
    Adrian
    I'm thinking about either changing the electronics to further calibrate a previously installed needle or if its possible to 3d print/mill a small guide for installing the needle. Type 2 Speedo PCBs have a different chip, these use a RCA 929xx type which is not available anymore unfortunately.
     
  4. 4valves

    4valves Rookie

    Aug 29, 2012
    9
    So at moment, we can't use for type 2 your great work!
    Do we have to wait till you will find different electronics ?
    Send speedo to you, for card exchange and setting, is not feasible?
    Thanks
     
  5. chrisgoates

    chrisgoates Rookie

    Nov 21, 2019
    1
    Full Name:
    Christopher Oates
    I have joined this forum in order to thank Adrian and other contributors to this thread which has enabled me to repair the Veglia Speedometer from an Alfa Romeo GTV6.

    The short version is that it was the BD370 transistor in the amplifier section that was faulty, I replaced it with a BD244C.

    The long version. It is a long time since I have owned a 1980’s Alfa Romeo but in the process of trying to clear out my garage I came across lots of spares. A few weeks ago I came across a GTV6 speedometer together with a lot of ex Fiat Veglia speedometers of the same era. I vaguely recall pulling these from Fiats in a scrap yard, I assume when I was trying to repair either my Alfa or Guzzi speedometers. I also had one complete sender. I was curious and hooking the sender up to an electric drill showed that some of the Fiat speedos worked but the GTV6 one didn’t. Here was the challenge, could I fix it? Two of the Fiats were of your type I with a SAY115Y chip, the remaining Fiat and GTV6 ones were of the Type 2/3 in that they all had an 8 pin DIP chip labelled RCA, but had several differences, the most notable being that the GTV6 one had 3 transistors.

    I experimented with a very old oscilloscope, basic signal generator and an audio amplifier and discovered that the working speedos would run with a square wave signal of about 8 volts and about 100 Hz, and a 12 volt power supply. My probing with the oscilloscope on the working units confirmed Adrian’s work that the square wave signal from the sender was processed to about 6 volts and input onto pin 1 of the chip which behaved as a frequency to voltage converter outputting a voltage onto pin 5 which varied directly with the frequency of the input. This voltage was processed through the two transistors and drove the dc motor which ran the speedo needle and odometers just like an old mechanical drive would, about 1-7 volts gave about 0-100mph. Feedback came from the motor sensor into pin 2 of the chip at approximately half the frequency of the pin 1 input and about 6 volts and I assume, but didn’t investigate further, modified the voltage put out on pin 5.

    There was no consistency of the markings on the 8 pin DILs apart from RCA, some were illegible. I tried to find a current IC that might perform the comparator function on two frequencies as well as converting to voltage, the LM2917 looked hopeful but my electronics knowledge was not sufficient to tell if it could be made to work. The pinout was different to the existing IC.

    I jumpered the motor drive from a working speedo to the non-working GTV6 one and the motor and motor sensor worked. I couldn’t see the tracks on the double sided circuit board well enough to draw a decent schematic, they were obscured by the components. I reverted to my usual fault finding technique of unsoldering and testing any burnt or damaged looking components (none in this case), then capacitors (all OK), then semiconductors. The BD370 transistor was faulty. An internet search revealed it was PNP medium power silicon but obsolete with a strange pinout. I substituted a BD244C which had similar characteristics but is physically bigger as higher power and twisted the legs to match the old pinout. It worked both with the signal generator and the Fiat sender driven by the drill.

    Chris
     
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  6. alhbln

    alhbln Formula 3
    Owner Consultant

    Mar 4, 2008
    1,660
    Berlin, Germany
    Full Name:
    Adrian
    It's not really a problem of the electronics but rather how the Speedo was designed for production. Marelli simply removed the possibility to calibrate the instrument after it had been assembled. I was thinking of adding a calibration option, so you could install the needle as usual and then fine tune.
     
  7. BigTex

    BigTex Seven Time F1 World Champ
    Rossa Subscribed Owner

    Dec 6, 2002
    71,035
    Houston, Texas
    Full Name:
    Bubba
    Welcome Chris!!

    Wonderful thread.....]
     

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