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Repair Of Rear Led Lights

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At last, a chance to feed some knowledge back into the forum!

My IS200 came with after market LED Stop/tail light units, no doubt sourced from "the other side of the World" by the original owner. Over time several LEDs had failed and I finally decided to cut the units open and replace the failures. The process turned out to be easier than expected and has been completely successful.

The light units each contain 23 LEDs - these are connected in 5 strings of 4 LEDs in series, plus one string of 3 LEDs. There are series resistors of 150 Ohms to limit the current in each string. I kept a sketch of the complete circuit for reference.

The circular plastic backs of the units can be easily cut away. I used a Dremel with a fine milling cutter (a used ex-dental type). There is no need to cut any of the outside visible parts, only the back which is completely hidden. There was a double plastic skin to cut through, the inner being what looked like a reflector for an optional standard bulb. After the back is cut away the LED circuit boards can be removed - held in by 2 screws. The only difficulty encountered was trying to remove the plastic swarf from the insides of the units.

The failed LEDs can then be replaced. An excellent match in terms of brightness and colour are the Farnell part 149-7975. These are 5,000mCd 5mm Red LEDs and come at a cost of 15p each +VAT at 25 off. If one LED fails then the whole string of 4 will go out, so it is necessary to find and replace the failed LEDs only.

The source of the problem is clearly overheating of the LEDs. The LED array draws much less current than a conventional bulb. To avoid the dashboard warning light coming on, resistors are arranged in the units to draw extra current, which is dissipated as heat. There was clear evidence of overheating on the circuit boards in the vicinity of the failed LEDs. The backs of the units can be re-attached with silicon and any LEDs which fail in the future can be easily and quickly replaced. I trust this may encourage anyone with the same problem to have a go.

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Good repair, bit of a silly way to increase current consumption.

I think the normal way is to fit ballast resistors but these have their own problems with suitable locations and wiring.

Technically each LED should have its own limiting resistor but like everything these days they are built to a price not a quality.

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