Lucas Opus Ignition 35DE8

Repairing and Modifying the ignition pick-up module

I thought I would share my experience in repairing the Lucas Opus ignition module fitted to my 34 year old car.  Sometimes it would not start, or driving only 200 yards the engine would cut out but could be restarted again.  After researching the intermittent problem I found that the OPUS  ignition system is unreliable and that there are various upgrade kits available. Because I’ve  had no problems for 34 years I decided to repair the module - after all it had been reliable till now and I wanted to keep the ignition system as original as possible. Bench testing the module with the intact rotor showed the PCB was intermittent when flexing. The silicone was removed to access the sensor L1 and other component connections. Resistance readings were OK as per the circuit diagram. However moving the transistor Q3 showed intermittent readings. There is no information available for the  Lucas 83448A transistor Q3 so fitted a BD135. The PCB was charred near the earthing solder tag. The track that feeds the base of Q4  [see photo below] was cracked, this was scraped and repaired. To improve reliability Q4 Motorola TEO1032 was replaced with a BU941ZP-FI together with a silicon pad insulator [pink in photo]. This Darlington transistor contains a protection diode so removed the wire link to D2.

To test the unit a bench power supply and a car stop lamp bulb was used. A note was made of the voltages. The photos below show the lamp illuminated when the ferrite is not in range, and off when in range of the sensor L1. Both the PCB and the sensor were heated with a hair-dryer, as I had heard the Sensor L1 may have a cracked ferrite E core - fortunately everything worked well.

Finally, instead of using a silicone sealant to protect the PCB, a Silicone Conformal Coating (SCC3) which has a good operating temperature was used. When the coating had cured, the solder tag was scraped clean to obtain a good connection to the earthing bolt.

The assembled module was fitted back into the 35DE8 distributor, ensuring an air gap of 0 .014”- 0 .016” between rotor and sensor. With the distributor cap off an old spark plug widened to ¼” was attached to the coil HT lead . Turned the ignition key and had a good fat healthy spark. Refitted the distributor cap and engine started first time! No further ignition problems for over a year! Total component and  coating  cost £17.

Click an image to enlarge group photos

Original ignition module V8

Original ignition module V8

PCB cracked print near solder tag

Original-35DE8-Ignition-module
Underside-Original-Opus-Ignition-module
PCB showing cracked print 35DE8

PCB sprayed with Conformal Coating

PCB sprayed with Conformal Coating

Repaired ignition module V8

PCB-treated-with-conformal-coating
Repaired-track-and-treated-with-conformal-coating
Repaired-Module

Repaired 5em Module

Bench testing - ferrite out of range

Bench testing - ferrite in range

 5em Opus ignition module 35DE8
Opus Ignition ferrite out of range
Opus Ignition ferrite in range

Module and leads

5em Module-and-leads-35DE8

Solder side diagram PCB

With acknowledgement to Gene Thompson - my modified diagram

35DE8-pcb-diagram-reverse

Circuit Diagram Schematic

Opus ignition Circuit Diagram Schematic
Repaired-module-Lucas-35DE8
Repaired Opus Ignition module and rotor 35DE8
Ignition module and rotor arm 35DE8
35DE8 Opus Ignition Ballast connection diagram

Lucas 35DE8 distributor pick-up module and base plate. Fitted to many Bentley, Rolls Royce, Aston Martin, Triumph, Rover SDI and V8s of the early 1980’s.

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