1989 Digital Cluster Power Supply

Location of the 89 Power Supply

 

Symptoms of a defective Power Supply

  1. The backlighting doesn't light or lights intermittently, even after you've repaired the more common board connector issue.

  2. Segments of the LCD panels flicker randomly (might be difficult to see without the backlight working)

  3. The 5A LCD fuse blows with the cluster connected, and doesn't blow when the cluster is disconnected.

 

Troubleshooting the Power Supply

  1. The schematic for the 1989 C4 is here: Click Here

  2. Remove the 5 screws holding the metal back onto the digital cluster.

  3. Physically examine the supply - look for charring, leakage, traces of smoke damage, etc. Fried electronics have a distinctive smell, so give it the sniff test. This can help you localize the problem.

  4. See my article on Bench Testing the Cluster for info on powering up the cluster while it's out of the car.

  5. Locate the 470uF capacitor on the top board near the board connector. Measure the DC voltage across its terminals. It should measure +5.0V. If so, the power supply is likely working.

  6. Measure the AC voltage across the terminals of the 470uF capacitor. It should measure less than 50mV. If it's higher, the filter capacitors might have failed. Suitable replacements are available in our power supply rebuild kit

  7. Measure the DC voltage across the 10uF capacitor on the top board, near the board connector. If it's not +5V, there is a problem with the standby voltage regulator. Suitable replacements are available in our power supply rebuild kit.

  8. Measure the DC voltage between the junction of R196/R197 (+) and ground (-). This is the turn-on signal for the power supply. It should be less than 0.6V to turn on the power supply.

  9. If the power supply appears to be working correctly, the problem may be with the cluster and not with the power supply.

  10. There are many electrolytic capacitors on the power supply. Age tends to cause the caps to dry out and short. This can cause the LCD and/or CLSTR fuses to blow. Suitable replacements are available in our power supply rebuild kit.

  11. The power supply has a MOV between gnd and +12V. An overvoltage or reverse voltage can cause this to fail. This is a protective device, so if it's bad, it won't cause problems, but it leaves the cluster unprotected from power surges. If this is bad, it may be physically damaged/charred. A suitable replacement is available in ourpower supply rebuild kit.

  12. If you have an oscilloscope, measure voltage across the base of Q18. It should be a square wave, 50% duty cycle, and 20KHz.

  13. If you have an oscilloscope, measure the voltage at the collector of Q18. It should be a square wave of 50% duty cycle and ~25kHz. Measure the collector voltage. It should be the same 12Vpp, 20KHz square wave measured in the previous step. If the base is a square wave and the collector is not a square wave, the switching transistor is probably bad.

 

Rebuilding the Power Supply

The replacement power supplies which are available for 84-88 Vettes won't work on the 89s, as the 89 power supply is no longer a separate, replaceable board. We now sell a kit of parts to rebuild the 1989 Corvette Digital Cluster power supply. It includes electrolytic capacitors to replace all in the cluster, a new switching transistor, +5V regulator for standby power, switching diode, Metal Oxide Varistor and more.

 

Click Here for Power Supply Rebuild Kit

New Power Supply Parts Kit

Locations where the new components should be installed

Another view of component locations

 

Cautions

  1. The solder we included contains lead. Take reasonable precautions when handling it: Don't hold it with your mouth, don't breathe the solder fumes it creates, and wash your hands after handling the solder and before eating.

  2. If the components have tape attached to the terminals, cut away the taped portion of the lead. Don't try to peel the tape off or the solder to the lead with tape residue - it won't work.

  3. The kit contains the parts we commonly see needed in a power supply rebuild. You probably don't need to replace ALL of the components in the kit. If you end up needing components not provided in the kit, let me know and I'll attempt to find a source and include them with future parts kits.

 

Parts Replacement

Note: - The numbers on the images above correspond to the components in the list below.

  1. Replace the capacitor marked 33uF on the part and C115 on the schematic/board. Be sure to mark the board with a sharpie to indicate the (+) and (-) terminals, and be sure to match the polarity markings on the new component to the markings you made on the board.

  2. Replace the capacitor marked 150uF on the part and C110 on the schematic/board. Be sure to mark the board with a sharpie to indicate the (+) and (-) terminals, and be sure to match the polarity markings on the new component to the markings you made on the board.

  3. Replace the capacitor marked 150uF on the part and C38 on the schematic/board. This is located near the odometer connector on the top board. Be sure to mark the board with a sharpie to indicate the (+) and (-) terminals, and be sure to match the polarity markings on the new component to the markings you made on the board.

  4. Replace the capacitor marked 10uF on the part and C112 on the schematic/board. Be sure to mark the board with a sharpie to indicate the (+) and (-) terminals, and be sure to match the polarity markings on the new component to the markings you made on the board.

  5. Replace the capacitor marked 470uF on the part and C116 on the schematic/board. Be sure to mark the board with a sharpie to indicate the (+) and (-) terminals, and be sure to match the polarity markings on the new component to the markings you made on the board.

  6. If needed, replace the switching transistor, Q18.

  7. If needed, replace the MOV - this is blue in the kit we sell. To remove it, you will need to cut the heat shrink, and reattach the new component with hot glue or another adhesive.

  8. If needed, replace the switching diode, marked CR49 on the schematic/board. It is located next to the switching transistor, Q18. Be sure to install it with the cathode (white band) side facing the same direction as the factory part.

  9. If needed, replace the Standby Voltage Regulator marked 7805 on the part and VR1 on the schematic/board. The flat side should face the 470uF capacitor.

 

Replacing the Power Supply

The replacement power supply we sell is for 84-88 models only. This will not work in an 89 cluster, as the power supply is integrated into the top board, rather than being a separate board like the 84-88s.