Checking your RS4.5 Crossovers for dry joints

The following fault diagnosis applies to the RS4.5 crossover but is equally applicable to any crossover that uses a PCB and is quite old or has poor solder joints.

Recently I was doing some near field testing of my RS4.5's when I noticed I dip in the output of 3-4 dB of one of the speakers(left) around 100Hz and upwards compared to the other speaker which was virtually flat from 30Hz upwards. Because sound is fairly non directional at these frequencies problems can sometimes go unnoticed when one good speaker is masking the fault of the other so a quick test with an audio generator and sound level meter can sometimes be an invaluable diagnostic tool

I noticed when I switched the bass equalizing switch on the crossover the bass would sometimes come up to normal so I immediately suspected a dirty switch. But on closer inspection I notice the 300 uF bipolar cap that feeds the two series connected four ohm voice coils was loose on one of its solder lugs. Thinking the worst I thought the terminal on the capacitor itself had come adrift meaning that I would have to chase up a replacement



I removed the crossover board and inspected the board more closely then I could see the problem. The previous modifications to the wiring allowed me to easily remove the crossovers. The capacitor had a dry joint on this leg and was making intermittent contact. The following picture illustrates the problem. Note that the black grunge around the joints is not flux but is the remnants of the old foam rubber sealer which is no longer used.



Whilst I had the crossover out I decided to go over the whole board and resolder all of the joints just to make sure. Previously when I rewired these RS4.5's I made provision to be able to easily remove the crossovers so I decided to resolder the joints on the crossover from the other working speaker as well. Needless to say the speaker is now fixed The morally of the story is always carefully inspect old solder joints and if in doubt redo them