86 Digital Cluster [Archive] - Father Larry's Corvette Shop

fatherlarry

06-27-2004, 01:06 PM

Dave,

When the 1984 Corvette was released, its digital dashboard was revolutionary. For the first time, information was delivered electronically and not by analog gauges or tell tale lights. For the most part, the digital dash has proven to be very reliable over the years, however the cluster can fail for various reasons. The main problems are poor grounds, corrosion on terminals and burnt-out bulbs. Since the LCD cluster was first introduced, it has been regarded as an Exchange-Only (No Repair) item by the dealer. This article will cover the three most common failures that you can repair yourself. Why pay $300.00 or more to have someone change a bulb or clean the terminals?

Changeable Parts And Cluster Repairs
Items that can be changed by the owner or dealer

• One or all four halogen 882 light bulbs on the 1984-88 are changeable by the owner. The 1989 cluster has Xenon bulbs,
which are replaceable with 7073 Stanley bulbs (not soldered in). The dealers do not have this bulb. I know of only two sources for them.
• Service exchange clusters at GM dealerships. This requires the odometer be removed from the defective cluster, then reinstalled in the exchanged cluster
• The odometer motor is changeable by the owner.
• Directional and high beam indicator lens and # 74 bulbs.
• Odometer motor lens.
• Photo sensor lens.
• Bulb heat sinks.

Cluster Power And Grounds

The LCD (liquid crystal display) of the cluster is controlled by the cluster's microprocessor via the CPU (central processing unit) and A/D (analog / digital) converters.

The cluster photocell, which senses the light inside of the car and brightens or dims the cluster's four halogen bulbs. These number 882 halogen bulbs are replaceable on the 1984-1988 clusters. The 1989 cluster uses a Xenon bulb, which is also replaceable. The 1984-1988 cluster's bulbs are rated at 3.8 candlelight power and the average life is estimated between 1,500-3,000 hours of continuous use.

When the parking lights are turned on the cluster goes into a photo cell over-ride and a limited dimming control is obtained by turning the head light switch knob. The 1984-1989 clusters have one 32-pin connector and one 24-pin connector
.
The 32-pin connector is used for power, grounds, sensor signals and output signals. The 24-pin connector is used for driver information switch input signals. The large connector contains the ignition-on signal's 12 volts, constant power for microprocessor memory and grounds going to the chassis and engine. Cavity D1 is a black ground wire going to the IP harness wire to the IP ground at the left dash at the door hinge pillar area. Cavity D3 is a black-white stripped ground wire going to an ambient over-ride sensor under the left dash, through the bulkhead connector, then to the ground on the left rear of the engine. This location was moved several times. For 1984-1985, to the top left transmission bell housing bolt. For 1986-1987, to the negative cable bolt to engine. For 1988, to the transmission left lower bell housing bolt stud (nut on stud). And for 1989, the D3 ground wire goes to the ambient over-ride sensor then to the right dash engine harness connector then to the transmission left lower bell housing stud (nut on stud).

Cavity D5 is a constant 12 volts DC coming from the (orange wire) LCD fuse. This powers the cluster microprocessor's memory. Cavities D16 and C16 are 12 volts DC ignition-on power pink-black wire coming from the cluster fuse. If the cluster has a ground on D1 and D3, 12 volts cavity D5, 12 volts D16 and C16, the cluster should light up. There is a normal 3.5 to5.0 milliampere draw on cavity D5 circuit. This is for the cluster microprocessor's memory. The normal car draw is from 18 to 22 milliampere. When checking a ground, always use a digital volt ohmmeter. With the ohmmeter 's black lead to the uniframe or negative battery and the ohm meter's red positive lead to the ground wire or component, the closer the meter reading is to zero or 0.10 ohms indicates a good ground. A poor ground will show high resistance.

Do not use test lights to check for voltages. The Corvette electrical system is sensitive to specific voltages. For example, if your cluster has malfunctions and you use a test light to check the voltages on the cluster or LCD fuse, the light would come on showing OK. Using a volt/ohm meter, the voltage showed 9.8 volts. This could cause a malfunction in the cluster.

Common Problems

One of the most common problems is the dash lights will go dim and the high beam and turn signal lights come on. When the dash lights are inoperative and the high beam and directional indicators come on dim, look for a bad ground. The most common problem is a poor dash ground on the 153 circuit. This is a black/white striped wire in cavity D3 of the large connector to the cluster. This wire goes to an ambient over-ride sensor , then to the bulkhead connector to cavity B1 to the engine harness wire to the left rear of the engine.
The ambient over-ride sensor is located under the dash on the backside of the bulkhead connector on a plastic cover over the wires entering the connector. It is about the size of a dime and 1/2-inch thick with two terminals. One is the 153 circuit. The other returns to the cluster to cavity D7. This is a 911 circuit and is a dark blue wire. The purpose of the ambient over-ride sensor is when the temperature drops low in the northern areas the LCD will still illuminate.
Ground the 153 circuit, black/white stripped wire, by attaching a ground wire at the over-ride sensor. Then route it to the left door hinge pillar and attach it with a screw to the hinge pillar. If it works or doesn’t work just leave it grounded. If the ground is good and the dash is still inoperative, the cluster may have to be removed and the board terminals cleaned as described in Interface Connector Cleaning Procedure.

CORRISON ON TERMINALS
Interface Connector Cleaning Procedure and Combination Bulb/Socket Replacement
No internal parts are sold for the cluster. A common cause of an intermittent component operation in the cluster is where the rear circuit board plugs into the forward circuit board.

1.Remove the cluster from the car. Refer to the Cluster Removal Procedure.

2. Lay the cluster face down on a smooth flat surface covered with a soft towel. Always be careful not to scratch or damage the LCD screens because they are very costly to get repaired. If these are damaged, there usually is an extra service charge to get them replaced.

3. Remove the 7/32 mm screws holding the metal back plate to the cluster housing. Lay the metal plate to the side.

4. Unplug the odometer-motor wire connector from the circuit board. The 1984-88's have two wires in the connector; the 1989 has four wires in the connector.

5. Remove the three 7/32 mm screws holding the odometer to the cluster.

6. To access the interface connector, remove all of the shiny 7/32 mm screws holding the upper circuit board to the cluster housing.

7. Once the screws are removed, take hold of each end of the circuit board and carefully lift straight upward in order not to bend the terminal pins. This unplugs the board from the cluster and the lower circuit board. Do not try to remove the lower board and LCD screen modules. You cannot buy these anyway.

8. You can now see the terminal pins interfacing to the removed circuit board. To clean these terminals, use some electrical contact cleaner on a cotton swab. Do not spray directly into the cluster. Be careful not to let any cleaner touch the LCD screen modules.

9. Also carefully clean the contacts in the connector in the upper right corner of the removed circuit board.

10. As you can see, you can easily access the sockets holding the halogen or Xenon and directional and high- beam indicator bulbs at this point. While you have the upper circuit board removed, replace the halogen or Xenon,directional and high-beam indicator bulbs, socket and all. Just turn the socket and lift to remove both the bulb and the old socket. As you can see, these sockets get very hot.

11. Reverse the removal procedure to reassemble the cluster.

Replacement Of Bulbs (Without Sockets) Without Removing Cluster From Dash
Changing the 882 halogen bulbs in the 1984-88 cluster:
The 882 halogen bulb for the 1984-88 cluster can be purchased with or without the socket at most auto parts stores. For this replacement without removing the cluster from the dash, you don’t want the socket, just the bulb. The Xenon bulbs in the 1989 cluster are replaceable with 7073 Stanley bulbs (not soldered in). It looks like a T60, 194 wedge-based bulb. The 194 has a 2 candlelight power while the Stanley has a 3.5 candlelight power.

1.Remove the Cluster Bezel. Refer to Cluster Removal Procedure steps 1-6.
2. Once the cluster bezel is removed, lift out the shiny heat sink covering the halogen bulb to be changed.
3. Using a pair of needle-nose pliers, remove the defective bulb. After the new bulb is inserted into the socket, gently push the bulb into the socket, fully seating it to the socket.
4. Using a soft cloth or a cotton swab dipped in alcohol, wipe any fingerprints off the bulb. The oil on your fingers can cause early bulb failure. Bulb life expectancy is 1,500 to 3,000 hours of continuous use.
5. Reverse the removal procedure to reassemble.

Changing the Directional or High-Beam Indicator Bulbs:
The directional and high beam indicator bulbs are a small number 74 wedge-base bulb.
Remove the black lens cover by lifting out the two black plug retainers to access and change bulbs.
To remove the bulb, pull straight out on the bulb with a pair of needle nose pliers. Always wipe off the end of the new bulb after installing it. It is not a halogen bulb; but the oil off your fingers can cause a later failure. Reassemble all components as necessary.

Cluster Photo Cell Operation and How It Effects the Cluster
The photocell sensor is located at the top left of the cluster. When the light level in the car is low, the photocell dims the dash lights. When the light is bright, the dash lights are also bright.
When the park lights are on, the dash receives a variable voltage of 9.5 to 12 volts DC from the instrument fuse and the cluster goes into a photocell override. There is a limited dimming from the variable rheostat in the headlight switch. This can be changed by turning the head light switch knob. The photocell is a part of the cluster (not customer serviceable). The cluster repair is needed if the photocell is bad.

Simple Tests:
Test 1. Hold your finger over the photo cell lens (park lights off) and then turn on ignition key. The dash should be dim.

Test 2. With ignition key still on, remove your finger and shine a light onto the photo cell (park lights off). The dash lighting should get brighter.
Test 3 (Park Light). Put your finger over the photocell lens and turn on the ignition key. Then turn on the park lights. The dash should get brighter. The dash is generally dimmer when in the photocell override mode. If the dash lights don't seem as dim or bright as you would like, compare the lighting to another 84-89 Corvette by doing the same test.

Component Removal Procedures
1. Lower the steering wheel to the lowest position. Remove the tilt lever by turning counter clockwise.
2. Cover the top of the steering column, next to the IP with of 2-inch strips of masking tape. Also, place the 2-inch masking tape across the dash panel below the cluster bezel to protect the dash plastic.
3. Remove the head light switch knob by pushing a small screw driver rearward in the knob's slot. The shaft will stay in the head light switch.
4. Remove the Phillips screws holding the radio control dash bezel and set the bezel to the side.
5. Remove the three Phillips screws holding the cluster bezel to the left outer IP.
6. Remove the Phillips screws holding the cluster bezel to the IP and set the bezel to the side.
7. Remove the three Phillips screws holding the IP carrier to the IP pad. These screws are pointed upward in front of the top cluster's edge.
8. Remove the two vertical Phillips screws holding the center IP to the IP pad.
9. Place a 1-inch block between the IP carrier and the IP pad in the center IP above the radio. This releases any pressure on the cluster for easier cluster removal.
10. Remove the four 7 mm headed screws holding the cluster to the IP carrier--two above the steering column and one on each top cluster corner . The cluster is now ready to be removed.
11. Gently tilt the cluster's top rearward and to the left, clearing the steering column.
12. Locate the cluster's two connectors. Pull on the connectors, and then take a screwdriver and place under the lock tab to unlock the connector's lock. You should hear a click sound. Unplug the connectors and remove the cluster.
13. To reassemble, reverse the above steps.
If the cluster is to be sent out for an exchange at any Chevrolet dealer, the odometer motor will have to be removed and reinstalled in the new cluster. For repair elsewhere, the odometer stays in the cluster and you get your OEM cluster back.

Odometer Motor Removal Procedure
After removing cluster from dash using the above procedure:

1.Place the cluster face down on a soft towel on a smooth surface
metal rear cover on top).
2. Remove the 7/32 inch headed screws holding the cover to the cluster and lay the cover to the side.
3. Locate the wires coming from the odometer motor to the PC board and unplug the connector.
4. Remove the three 7/32 inch headed screws holding the odometer to the cluster.
5. To reinstall the motor assembly, reverse the above procedure.

Hope this helps....good luck and let us know how you make out.