Every so often, one of us encounters a problem whereby the empeg thinks it is on AC Power (rather than DC Power) when in the car sled. This causes all sorts of misbehaviours, such as not dimming when the headlights are on etc..

The usual culprit is the AC Power jack (yeah, it's really a DC Power jack, but humour us) at the back of the empeg, which incorporates a switch contact that is normally grounded when in-car, and normally floating (not connected to anything) when an AC Adapter is plugged in. The switch contact is the one soldered to the side pad of the AC Jack, just above the black jack in the photo below.

I ran into this problem during my recent Impreza installation. At the time, I just switched empegs and carried on with the install. But today I had a closer look at the b0rked unit.

The AC jack was just fine, so after a bit of signal tracing and probing with a multimeter, the culprit turned out to be a failed diode. The diode is in series with the switch contact of the power jack, to protect upstream components in the event that a reverse polarity PSU gets accidentally connected.

The empeg (RioCar) uses a BAS16 3-pin SMD diode for this, one pin of which is surplus. Once I located the diode on the circuit board, I tested it using sled power both with and without a dummy plug inserted into the AC jack. With a plug, the output of the diode correctly showed +5V (due to a 12K pull-up on it). But with no plug inserted, it showed 2V rather than the expected 0.5-0.8V. Which meant the diode was exhibiting much higher resistance than expected. Re-soldering the contacts didn't help, so.. dead diode.

I pulled a similar 3-pin diode from a dead video card, and after comparing datasheets/pinouts, decided it would work as a replacement, and now "pinky" (the player) is working correctly again.

So.. for the next time this happens, we now have a record of things here. smile


Description: New diode installed in place of the failed original.