Failed solder joint makes car clock go dark

-March 02, 2015

A few years ago, the clock display on my 2001 Subaru Forester went dark. The display lit up again a few weeks later and showed the the clock was keeping time but not always displaying it. A few days later, the clock went dark again. It remained that way for another few weeks before illuminating again. A new clock would cost more than $200—not worth it, even if I were to install it myself.

Assuming this problem occurred on other Foresters, I searched online. Sure enough, someone provided detailed instructions on how to fix the problem. A 30 Ω resistor had a poor solder joint. When the clock's board was manufactured, no solder paste was added on one end of the resistor. The solder joint relied on the solder from the SMT resistor and the board, which was not enough. Over time, the connection between the resistor and board failed because of vibration and temperature fluctuations.

A dab of solder fixed the problem—for a few years. When the display again went dark, I assumed another solder joint had failed.

The clock is running, but the display is dark.

With my nephew taking the pictures, I removed the clock module. A quick pry with a screwdriver revealed a four-terminal connector. Clearly, two wires power the clock, and two power the display. The connector unplugged easily.

Taking the clock inside, I removed it from its case and looked for a cracked solder joint, but none was visible. Thinking that the crack was too small to see, I checked the connections with a multimeter. All seemed good, but maybe that was because the warmer indoor temperature had caused enough thermal expansion to remake the broken connection.

The clock board has two 30 Ω resistors and one 51 Ω resistor. Not knowing which might have the intermittent solder joint, I heated all the connections around the resistors with a soldering iron. We took the clock module to the car and attached to the connector before putting the clock back into its housing.

The photos below show the steps needed to remove, repair, and replace the clock.

A screwdriver is all that's needed to pop open the clock's housing.

Once the clock is free, its four-pin power connector is visible.

Pressing a tab allows the connector to slide out from its housing.

Once we went inside, we removed the clock module from its plastic housing.

Though the connections around the power resistors tested OK with a multimeter, we took no chances. Touching up the solder connections on a few resistors should repair the failed connection.

Before assembling the clock board back into its housing, we went back to the car
and connected it. The display worked again.

The clock is back in its housing. Now we can see the time without looking at our phones.

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