W123: Instrument cluster Printed Circuit Board repair

[whunter]

W123.

* Any issues with the instrument cluster?

Just went through this on a friends W123, left side circuit board damage.
Repaired with a pen application printed circuit repair paste from RadioShack, fiberglass brush/cleaner + paste under $30.00.
How to repair a PCB Trace?

Note: READ the directions on the repair past regarding drying time before using it.

#1. Remove the cluster from the car.
#2. Remove the eight Philips screws from back of the cluster.
#3. carefully remove the speedometer, tachometer/clock, and fuel/oil/temp gauge from the lens housing.
#4. You will be working on the fuel/oil/temp section.
#5. Remove the 7 MM nuts (back of board), don't loose the washers = two per nut.
#6. Remove the two slotted screws (oil pressure).
#7. Gently/firmly separate the fuel/oil/temp gauge from the circuit board = there are four electrical pins dis-connecting.
#8. Warning: there is a brown nylon insulation Disc between the circuit board and oil gauge, it MUST be re-installed before assembly.
#9. the burnt traces are typically: right upper (inoperative right side cluster running lights) and hidden under the lower portion of the gauge (battery charging).
#10. Use the fiberglass pen tip (dipped in acetone) to gently clean the insulating coating from (roughly) 3 - 4 MM on each side of the burnt circuit trace area.
#11. Lay strips of tape on each side of the burnt printed circuit before applying the repair paste.
#12. Apply the repair paste.
#13. Allow the paste to dry for approximately three minutes.
#14. Cautiously remove the strips of tape. Note: if the repair paste comes off with the tape repeat steps #11 - #13 as needed.
#15. Re-assemble the instrument cluster.
#16. Install the cluster enough to test the electrical circuits, DO NOT START the engine without connecting the oil pressure line!!!


Note: this paste is also used to repair rear windshield heater grids.

Field expedient upgrade:
On the rear of the fuel gauge circuit board there is a square tab (screw mounts through it) grounding the speedometer assembly.
Make/install a ground wire with two spade connectors in the center, mount it from the square ground point to a solid body ground.
This reduces/eliminates most instrument cluster electrical issues.
The spade connectors in the center of the home made ground wire are for easy instrument cluster removal in the future.