how to replace the electronics in a 12v classic car clock.

Discussion in 'Technical Repair' started by Jamesmansfield, Sep 26, 2016.

  1. Jamesmansfield

    Thread Starter New Member

    Aug 26, 2016
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    My First Thread, I apologise for any mistakes.
    I have a classic car clock that is running at double speed i.e. 30 sec to do 1 min, it has a very simple circuit and seems to be a larger version of the normal quartz wall clock, it has a coil that needs a momentary 12v pulse every 1 second which reverses 180 degrees every alternate pulse, my issue is that I cannot identify the crystal frequency and the chip is no longer available (please see attached pictures) my original idea was to replace the components, which I did the resistors and capacitors although they were testing fine. I could replace the clock but I want to keep the dials original, I also like a project. Would anyone on the forum have any ideas for a circuit I could use to replace the chip or an equivalent chip as I cannot find it in my old reference books. I have looked at 555 timers but they do not seem accurate enough, I have also found a thread on using a 1.5v wall clock inards but due to the reversal pulse I am having difficulty increasing the output to 12v.
    many thanks
    Jim IMG_4237.jpg IMG_4238.jpg
     
  2. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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  3. Kermit2

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    Feb 5, 2010
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    Go to a junk yard. Get a brand new used one.
     
  4. Jamesmansfield

    Thread Starter New Member

    Aug 26, 2016
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  5. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The Xtal used now in clocks is 32.768Khz, which is a power of 2 (8000hex) represented by 15 bits and rolls over every 1 sec.
    It is very simple to make a clock from a small pic that has xtal input for Timer1.
    Max.
     
  6. crutschow

    Expert

    Mar 14, 2008
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    I had a battery powered wall clock that also suddenly started doing the same thing.
    I suspect that it started operating at the crystal second harmonic overtone due to either a change in the crystal or one of the small associated crystal load capacitor(s).
    You might try adding a small capacitor (10pf-20pf) from either or both of the crystal terminals to ground to see if that has any effect.
     
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  7. Jamesmansfield

    Thread Starter New Member

    Aug 26, 2016
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    I have ordered a new crystal, thanks I am going to try the capacitors as well.
     
  8. RichardO

    Well-Known Member

    May 4, 2013
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    Is this a mechanical clock? The shape of the PCB and the small IC pin count makes me think so. It might be a mechanical or electrical problem in the motor if it is.

    Also, the crystal seems awful large for a typical 32,768 Hz crystal. Maybe they were larger when the clock was manufactured or the auto environment dictated that larger size?
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Mercedes were using this IC in their clocks in the early 60's so I am guessing that there was not the demand for miniature watch crystals at that time.;)
    If it is not digital, it is (semi-clockwork) mechanical.
    Max.
     
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  10. RichardO

    Well-Known Member

    May 4, 2013
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    Duh. Read all of the original post.

    Obviously a clock motor driven like digital watch motors. I think that it is probably a 8.192 MHz crystal divided down and split into the two phase pulses for the motor.
     
  11. MaxHeadRoom

    Expert

    Jul 18, 2013
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    ?????????o_O
     
  12. RichardO

    Well-Known Member

    May 4, 2013
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    I meant that I had re-read the post and realized that the poster had already said that the clock had a moter. :oops:
     
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  13. Jamesmansfield

    Thread Starter New Member

    Aug 26, 2016
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    Hi All,
    crystal replaced, still double the speed (counted the pulses 60 in 30 seconds, so not a mechanical problem), waiting for the 10pf capacitors to arrive to see if that helps, Max you mentioned a PIC to could do the job, I tried PIC programming a few years ago an to be honest it was beyond me kept getting very strange result with the programming, do you have a circuit and the code for a project like this,
    thanks all for your help
     
  14. MaxHeadRoom

    Expert

    Jul 18, 2013
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    This is the original code I found and used in a project, but I converted it for the 18F series.
    It just flashes a LED every 1 second, so it should be relatively easy to adapt it.
    It uses a 32Khz crystal on T1OSCI and T1OSCO
    Max.

    Code (Text):
    1. ;=======SECONDS.ASM=================================9/30/02==
    2.         list    p=16f870
    3.     __config  h'3f71'
    4.         radix   hex
    5. ;------------------------------------------------------------
    6. ;seconds demo
    7. ;    external oscillator, 32768 Hz, timer 1, prescaler 1:1
    8. ;------------------------------------------------------------
    9. ;       cpu equates (memory map)
    10.  
    11. ;------------------------------------------------------------
    12. ;------------------------------------------------------------
    13.         org     0x000
    14.     goto    start    ;skip over location pointed to by
    15.             ;   interrupt vector
    16.     org    0x004
    17.     goto    iserv
    18. ;
    19. start:
    20.         bsf        STATUS,    RP0  ;switch to bank 1
    21.         movlw   b'00000000' ;port B outputs
    22.         movwf    TRISB
    23.         movlw    b'00000110' ;turn off A/D, port A
    24.         movwf    ADCON1
    25.         bcf        STATUS,    RP0  ;switch back to bank 0
    26.         movlw    b'00000000' ;port B lines low
    27.         movwf    PORTB
    28.         bcf        INTCON,    7    ;disable global interrupts
    29.         bcf        INTCON,    6    ;disable peripheral interrupts
    30.         bsf        STATUS,    RP0  ;bank 1
    31.         bcf        PIE1,    0    ;disable tmr1 interrupts
    32.         bcf        STATUS,    RP0  ;bank 0
    33.         bcf        PIR1,    0        ;clear timer 1 interrupt flag
    34.         movlw    b'00001010' ;prescaler and tmr1 setup,
    35.         movwf    T1CON        ;   tmr1 off
    36.         clrf    TMR1H    ;clear timer 1 high
    37.         clrf    tmr1l    ;clear timer 1 low, clear prescaler
    38.         bsf        INTCON,    7    ;enable global interrupts
    39.         bsf        INTCON,    6    ;enable peripheral interrupts
    40.         bsf        STATUS,    RP0  ;bank 1
    41.         bsf        PIE1,    0    ;enable tmr1 interrupts
    42.         bcf        STATUS,    RP0  ;bank 0
    43.         bsf        T1CON,    0    ;timer 1 on
    44. circle:
    45.         goto    circle
    46. ;------------------------------------------------------------
    47. iserv:
    48.         bcf        PIR1,    0    ;clear timer 1 interrupt flag
    49.         bsf        TMR1H,    7    ;set up timer 1 to roll over at
    50.             ;   32,768 counts
    51.         btfss    PORTB,    0    ;port B, bit 0 STATUS?
    52.         goto    setbit    ;bit is clear
    53. clrbit:
    54.         bcf        PORTB,    0    ;clear port B, bit 0
    55.         retfie        ;return from interrupt
    56. setbit:
    57.         bsf        PORTB,    0    ;set port B, bit 0
    58.         retfie        ;return from interrupt
    59. ;------------------------------------------------------------
    60.         end
    61. ;------------------------------------------------------------
    62. ;at device programming time, select:
    63. ;       memory unprotected
    64. ;       watchdog timer disabled (default is enabled)
    65. ;       standard crystal XT (using 4 MHz osc for test)
    66. ;       power-up timer on
    67. ;    brown-out reset enabled
    68. ;    lvp disabled
    69. ;    debug mode disabled
    70. ;============================================================
    71.  
    72.  
     
  15. AlbertHall

    Well-Known Member

    Jun 4, 2014
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    Jamesmansfield likes this.
  16. AlbertHall

    Well-Known Member

    Jun 4, 2014
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    The SAJ300R looks like it might be equivalent. See the attached pdf.
     
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  17. Jamesmansfield

    Thread Starter New Member

    Aug 26, 2016
    6
    2
    Thanks, that chip is the one, I am going to try the capacitors on the crystal then if that does not work then a new chip it is, thanks for everyones help.
     
  18. Jamesmansfield

    Thread Starter New Member

    Aug 26, 2016
    6
    2
    Thank you all for your help, It was the chip, now working perfectly.
     
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