W123: Instrument cluster Printed Circuit Board repair
 

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.

Pictures of supplies

Examples
 

Damaged circuit boards.

More Examples
 

Damaged circuit boards 2.

Cool, i love working on old circuits, so big and easy to get to. Unlike fixing a VW Bosch 5 abs cu, my eyes were bleeding after that one.

Thanks for posting this - that fiber glass pen looks really good - it might even help with the removal of the caked on sealant I've got on the edge of my windshields (still in the process of replacing the seals and refitting them)...

Being definately "challenged" does anyone know of someplace that repairs these circuit boards? The alignment area of my main plug was gone and someone plugged the board in wrong. Now, i have very little that wroks correctly: Turn signals, interior lights, climate control, etc.


Thanks,
Dave H...

These people have repaired several for local owners, average cost $300.00 - $500.00 USD.
Specmo Auto Speed & Sound
3189 South Dort Highway
Burton, MI 48529
(810) 744-2940


Suggestion:
Contact vstech through Private Message about a good used instrument cluster, he is in North Carolina.



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Thanks!
 

Roy,

(They ALL look "Burnt" to me every time.)

instrument and climate control lights not working
 

so i was given a 1982 mercedes 300d turbodiesel that had been sitting for 11 years. after just replacing the vacuum hoses and bleeding the brakes, it was road worthy once again. i quickly realized, as i started driving home in the dark, that the instrument lights and climate control lights did not illuminate when the lights were turned on. so i went home and looked up a few things about it, went outside, removed the rheostat, bypassed it, and all was well. all the lights lit up and it lasted about 2 months. during that time it worked well and i had no problems. i then noticed some change in my gearshift that looked like it had come out of a sewer. i took the wood grain paneling off and unscrewed the gearshift and removed the change and carefully reassembled it. soon after (not sure how soon but i wasnt sure if the gear shift was imperative to this issue) all the inside illuminated lights (instrument and climate) ceased to work. i tried cleaning the connectors, tried bypassing it with a different wire, (i got shocked by this, and the lights flashed on a few times, but it felt like there was a short in the 2 metal pins if thats even possible, and i couldnt get them to stay on) and even put the rheostat back on once with and once without the wire attached. nothing. i've gotten a little clip on led light that's magnetic and holds to the ignition tumbler and shines right on the speedo and other instruments, but im tired of it. is there any other thing that i could fix to get this to work right? money is kind of an object, seeing as i dont have much. is there a fuse or something? please help. thanks.

82 300dt 355,000 miles (Gold)

Question
 

Did you remove the fuel/oil/temp gauge section of the cluster and look for burnt traces?

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BUMPING because of addition at bottom
 

I am just about to do a similar repair. I have three burned traces. Th same one as in pirst pic above which goes to pin 15 - ground I think. Then the ones to 11 & 12 which are the rheostat.

I think I will hard wire them. I doubt that paste would carry much current. And I don't want to do this again soon :)

Here is a pic of my cct board:

http://dl.dropbox.com/u/54783344/123...r%20traces.jpg

ADDED: I soldered across the two pin sockets that the burned traces lead to/from (11 & 12). This essentially eliminates the dimmer and any need for the traces to and from it. I then ran a wire from those pins to another point that feeds the two dash bulbs. I didn't install LEDs, but if anyone is, this might be a way of eliminating those traces. I also ran a new ground wire from pin 15 to the main ground connector. It would also be easy enough to run another ground to the cluster bulbs that connect at top of board. That way, higher wattage bulbs may not blow any traces, but heat might melt the plastic (Maybe not with LEDs?)

It seems to me that there should be an additional fuse protecting the cluster circuit board lighting circuit. It feeds about 12 or 14 bulbs that vary from 1.2 to 3W - say 24watts. Would that mean 2amps when all are on? If something shorts on that circuit, the traces blow instead of the 8amp fuse that currently "protects" the circuit! Where to put fuse? It would need to be on the line that feeds pin 11. Size - maybe 2.5amps? But maybe someone would like to do a test and see what current it takes to blow one of those traces!

Any comments welcomed.

Good article Bill, well documented as usual . . . :)

Another way to use the "conductive paste" repair material is to use a toothpick. Apply from the tube to the toothpick and then transfer that to the ckt trace. You can make a much smaller line that way. Make sure to CLEAN the area with alcohol first especially if there's damage as shown in the video.

Graham, I would repair the traces using fine (30 gauge) wire-wrap wire. Clean the trace; use some liquid solder flux and lay the wire across the gap.

Using a soldering "station" iron (not a Radio Shack blunder-bus iron) set to about 600 degs, simply touch the wire with a tinned iron, and it will instantly flow and make a very, secure repair.

Put it this way, passing heavy current through that path will not open at the point again . . . ever!

Jim,
As I opined in my earlier message, it seems to me that those traces for the lighting circuit are a weak point in the circuit. Any overload and they will blow before the 8amp #1 fuse. I thought about fixing the traces and adding a fuse, but in the end decided to eliminate the dimmer circuit altogether and bypass the burned traces by running a wire to feed the two dash bulbs. I shorted pins 11 and 12 which really takes the cct board out of things so far as the center console lights are concerned. (small red circle in pic)

http://dl.dropbox.com/u/54783344/dimmer%20bypass.jpg

I should probably have run the red wire directly to the dash light connection on the board, but instead went to one of the dimmer connections, so I still have one lighting trace in use, but only for the dash bulbs. If I ever install LEDs, I will change that.

I decided to replace the burned ground trace by running a ground wire from pin 15 to the connector that the main ground screw connects to. (white wire in pic)

All the dash and console lights now work as they should.

It's actually quite amazing how much current that a typical PCB trace can handle.

For 2oz copper (typical), the following table shows the current carrying capability for various trace thicknesses:

Trace Width ---------- Current
0.025" --------------- 3.3 amps
0.050" --------------- 6.0 amps
0.10" ---------------- 9.9 amps
0.20" ---------------- 11.0 amps

It must have had much more current for it to blow as show in the pics.

Just for info . . . oops . . the first two line widths were mis-typed . . .