This week at Rewired, we investigated a fault causing intermittent highlight lifting on a Porche 968.
What was the Problem?
The customer experienced an issue with their headlights not always raising when turned on. Knowing the lighting control module was a common culprit, the customer found that if they wedged some cardboard between the module and the fusebox, the chances of it working greatly increased, hinting at a bad connection within that region.
The Investigation
With electronic modules of this age, it is common for the connections between a socket and the PCB to go bad over time, where the solder joint becomes physically compromised in its ability to sufficiently join the plug's pin to the PCB's trace pad. Common culprits include "dry" or "cold" solder joints.
A "dry" joint refers to a lack of solder being added to a joint during the manufacturing process, leading to a poor mechanical connection. Similarly, a "cold" joint is caused by a lack of heat provided when soldering, which prevents the solder from sticking to or properly flowing around the connecting metal surfaces. These issues lead to a weaker join that can fail over time, especially when exposed to stress from environmental influences, causing cracks, pits, and other deformities that hinder the electrical connection.
Poor solder joints can result in a disrupted or intermittent electrical connection, which can be further influenced by changes in heat/humidity or movement, improving or worsening the electrical conductivity of the joint. For example, take this broken connection to a relay inside the control module.
Upon close inspection of the circuit board, a small fracture was found in the solder joint for one of the relay's electrical connections. Similar fractures were examined using a microscope, such as these finer cracks discovered under the module’s main socket.
The Repair
To resolve this issue, the solder joints were reflowed with new flux and solder. Due to the thickness of the traces going to many joints, the board was lightly warmed with a heat gun to aid the thicker pads to take the heat from the soldering iron. Without the use of flux or sufficient heat, the new and old solder would not flow properly, leading to a bad mix, which will likely result in future cold joint issues.
All visible solder joints were reflowed, as there was no guarantee how reliable the currently unaffected joints would last. This will reduce the risk of additional joints failing in the future and help mitigate against the need for future repair.
The Result
After repairing the board and cleaning off any remaining flux residue, the module was ready for testing. Once the module was plugged in, the ignition was then switched on, and by manipulating the light switch, the lamps were controlled up and down effortlessly.
The lights were tested repeatedly to check that no hiccups occurred, and with that, the job was complete, all with another module saved from the bin!