The AC Controls don't dim with the Dash Lights
From Reader Bob Golden: This is a common complaint I have encountered. The dimming control for this display is controlled from and output of the Radio. It is a pulse with modulation feed and if the factory radio has been changed out you will not be able to control the AC display.
Broken Crystal? Y1 is part number 16017182
Bad microprocessor? U11 is part number 16033922
Flashes but data on screen OK? U9 may be bad. Can usually heat and cool to check this. Replacement is part number 16033919.
If C6 in power supply shorts, will cause Vsb (+5v) to go to 0V and will cause Voltage display and Oil Temp to climb. +5V regulator DM162 will get very hot.
Random flashes on display - could be a bad driver display.
Display flashes very rapidly? IC9 bad.
- Current drain on cluster? Check D5 for Draw: Off should be 1.0ma, On should be 150-180mA. If 150-180mA when off, the power supply could be bad, Q22 on a 1989 might be open (BAT), IC12 (no voltage on pin 6), IC15 shorted to ground or logic problem with IC11. Should be 5V on pin 6 of IC12 with ignition off.
- Speedometer readout quits above 85MPH (goes to zero)? C19 leaking/bad. Replace with .1uF.
- Temperature Gauge reading high? Could be a problem with Diode D10 leaking.
- Cruise Vac and Vent always on? C101 or C102 bad or installed backward.
Cluster tests (you need a cluster tester for this)
Cluster comes on OK but fails if turned on and off several times? Check CR4 (D4). It must not go below 4.7v or IC12 can reset on circuit.
Cluster OK until speed signal turned on? Could be a bad VFIA (IC3/VIA).