Repairing Intermittently Displaying Car Clock
W. Curtiss Priest
Center for Information, Technology & Society
466 Pleasant St., Melrose, MA 02176
Voice: 781-662-4044 BMS...@MIT.EDU
Fax: 781-662-6882 WWW: http://www.CyberTrails.org
Technical Note
July 24, 2000
1980-1992 Subaru Automobile
Repairing Intermittently Displaying Car Clock
(Flourescent green digital display style)
1988 Model DL
2 Wheel Drive
1800 cc
Single Point Fuel Injection (SPFI)
Preface: these repair notes are written for those who would
rather fix it themselves than purchase car repairs.
And, if you've collected enough electrical parts, you can
often do these repairs without leaving home!
Also, when you take into account the time spent bringing a car
in for repair and either waiting, or having to arrange other
transportation, you are often ahead in time, doing it yourself.
I do get occasional notes from mechanics at Surbaru garages
about why I would want to do this when the part is "only" $$.
They forget that they need only walk over to the parts counter
and spend your money on parts that cost many times the original
manufacturing cost.
***
This particular repair is very quick when you know what to
look for. You need not even disconnect the clock, so
access is about 10 seconds.
Total repair time is less than ten minutes.
***
Symptoms:
1. clock display goes dim or out
2. pressing one of the setting buttons may cause display to return
Repair:
------
Clock pops out of dash, lightly prying side
Remove 4 wires from back clip
Remove cover, prying slightly on clips
Unsnap PC board prying slightly on one of two side clips
Inspecting board:
----------------
Solder around power resistors looked "cooked" -- I shook off
loose solder by heating and tapping the PC board on the dash.
I checked for tinning on resistor leads. These looked good,
I resoldered, and there was no change in the problem.
(probably a good idea to resolder these anyway)
Flexing board caused display to change brightness.
Problem and Repair:
------------------
The 150 ohm 1/2 watt resistor to the left of the buttons
had a poor solder connection to the circuit trace running
to the buttons.
I resoldered that end of resistor. Clock got bright, no
amount of board flexing changed it. Clock was fixed.
Amusing:
-------
So, the reason the clock got brighter when an hour, minute,
or second button was pressed was because this flexed the
board, causing the 150 ohm resistor to "reconnect" due to
the mechanical flexing.
In Case You Wanted to Know:
--------------------------
The reason there are four wires running to the clock is:
1. Ground
2. Battery voltage for when ignition is off
3. Battery voltage for when ignition is on
4. Battery voltage for when you switch on parking or
head lights
(this causes the clock to be dimmer at night !)