240D Instrument P C board fried - PeachParts Mercedes-Benz Forum

ROLLGUY · #1 11-06-2012, 08:30 PM

My lights didn't work on my 240, so I pulled the instrument cluster. I found that one of the copper strips on the circuit board had a gap in it. I found my box of spare instrument parts, and the other one I had was bad as well. I went out back and pulled the cluster on my 240 project car, and it was fried as well! What's up with the circuit boards on the 240's? I have some 300D boards, but the wiring connector is in a different spot, and is different. I saw no bad parts on those boards. The circuit was easy to repair by soldering a wire between the gap. I guess I will have to look for these next time I go wreckin' yardin'.

PackerEdgerton · #2 11-06-2012, 10:04 PM

Simply put, the printed circuit boards on W123 instrument clusters were poorly engineered. Specifically, the trace that feeds all the current for the instrument lights is woefully undersized, and it heats up and breaks when the current through it exceeds it's capacity to deliver that current.

I have found that the 300D instrument panels are actually the same, electrically speaking, and if you move the plug UP and rotate it slightly to get it to fit, it WILL work properly. My 240D didn't have a lot of slack in the wire harness, and it made it hard to move the cluster in/out of the dash. However, it DID work just fine.

I ended up cleaning up the 240D's original cluster, and then doing just what you did - I soldered a heavy insulated wire over the broken trace. Just be careful, clean the trace where you intend to solder in the wire, and solder carefully, ensuring you have a nice clean solder joint.

Everything has been working splendidly for many months and many hours of nighttime driving now. While you're in there, make sure you have new bulbs in. I made the point of going to the MB dealership and getting the exact OEM bulbs. They fit perfectly, are the correct brightness, and everything is working just fine.

Sincerely,

Packman

ROLLGUY · #3 11-07-2012, 01:18 AM

Maybe the year that the clusters were made makes a difference. The clusters with the wiring connector lower and towards the drivers door seem to be fine. The three 240 boards that I have, all have breaks in the paths. The wiring connector is higher and more toward the center on these. I wanted to use a good one that I had, but the wiring connector is not in the correct spot, and the pins are in a complete circle with no gap. The 240 boards have a gap (1 or 2 pins missing). I am glad I was able to repair one of them....Rich