SDA CRS Crossover Problem After Replacing Capacitors

tiburonhombre

This is the second set of Polk SDA CRS speakers on which I have replaced the capacitors/resistors. The first build went mostly OK, after remembering to re-connect the tweeters all was well.

With this new re-capping, I have a problem on the right channel, the stereo module is not working, no sound out of the stereo speaker and tweeter. The dimensional speaker and tweeter work fine.

I kept detailed notes on the wiring connections and labeled each wire so I am fairly certain it is wired correctly. However, with Polk SDA circuits there are many opportunities to go wrong.


The interconnect cable works fine with proper working of the left channel stereo speakers and dimensional speakers.

I need some advice on troubleshooting the stereo module.

I removed the stereo module to confirm that there are no loose or broken wires. All capacitors are tight on the board. There are no breaks in the inductor copper wire. I reheated all the capacitor leads on the circuit board to make sure there were no cold joints. I also re-checked the connections to the new Cardas binding posts, all secure.

I tested the stereo module on its own by connecting a speaker and plugging in the speaker cable, turning on my amplifier and carefully turning up the volume. Questions is, will the stereo module work on its own without being connected to the dimensional module.

Is there anything else I can do to troubleshoot?

F1nut

Did you test the fuse?

Questions is, will the stereo module work on its own without being connected to the dimensional module.

Yes

tiburonhombre

Yes, checked the fuses, switched them from the left channel to the non-working right channel. I believe the fuses only protect the dimensional and stereo tweeters so the mid stereo speaker should still work with a blown fuse.

VR3

Don't put a resistor over a cap, the resistor will damage it if it gets hot

tiburonhombre

Good point, VR3, another problem to deal with. How about insulating the capacitor/resistor with a thin piece of silicone. Space is at a premium with those big 12V Mills resistors.

VR3

I've seen a resistor burn straight through a capacitor, I wouldn't keep them anywhere near each other

delkal

I put the resistors under the board when rebuilding. It gives you more room for just caps and any remaining inductors on top. You might have to drill a few extra holes

As for you problem no clue. But it is a good chance you soldered something wrong. Mark the bad crossover and pull both. Then compare them. The stereo portion should be wired identically. I never rebuilt an SDA but IIRC the dimensional speakers are not identical and the wiring is reversed at one point.

tiburonhombre

Good advice. I think the problem lies with the stereo module not getting all the signal from the binding post or inductor and will focus on that. I have one working stereo module in the left channel and will compare. Since Polk originally placed the caps on top of the ceramic resistors, I thought it would be OK to do the reverse. There is some risk of overheating in hindsight. Dave Shirley of DHS Speaker recommends placing them under the board also.

delkal

Use a DMM and check the resistance from the posts to various points of the 2 crossovers. The resistance should match in the stereo potion. An even quicker test is to check the resistance between the posts. It should be the same for both speakers.

RTally

One thing to remember is heat is the enemy of caps. I notice that the resistor is soldered to the cap leads at the point the leads exit the cap. If your soldering technique is not perfect (heat applied longer than necessary, too high of an iron temperature, repeatedly applying heat, etc), the cap can be damaged.

It is best to make solder connections away from the capacitor body. For those cases where the connection must be made closer, a heat sink should be used between the solder point and the cap body.

tiburonhombre

The issue is resolved:

• I had both the positive and negative input going into the positive binding post. It is confusing, since all the wires inside the binding post cup are white.

• The negative binding post white wire goes direct to the negative input on the circuit board.

• Two white wires coming from the fuses attach to the positive binding post and the positive signal for the circuit board looks like it comes direct from the inductor to the circuit board, anyway from the other side of the cup.

• The resistors were removed and relocated to the underside of the board, standing them off the board about 3/8". (a hemostat clamp was used as a heat sink when desoldering the resistors from the capacitors.

• Screws were removed, cabinet then drilled out to accept 8-32 hurricane nuts. (recommend using J-B Weld to attach nuts to back of particle board motorboard)

• The stock speaker gaskets were discarded and replaced with Mortite. At first, Mortite seems a bit messy but caulking stays pliable, seals absolutely and mostly completely removes without sticking excessively.

• Dacron speaker cabinet acoustic insulation was discarded and replaced with 2" egg crate foam.

• The stereo and dimensional speakers all work as intended. Modifications improved speaker clarity, brightening both the mid range speaker and tweeter, improved spatial sound and overall pleasing. For now, I kept the dimensional tweeter and will consider the RD 0194-1 tweeter upgrade. Speakers are used in a 3.1 sound system for left and right channels.

I thank all of you for your comments and suggestions leading to a positive result.

pitdogg2

I'm sorry but that mortite well be a major pita if you ever need to remove a driver. Armacell would have been a much better choice. Take it from us who have been there. We no longer use it for good reason.

Good job on finding the issue 👍

F1nut

NEVER use Mortite.

Use 5 minute epoxy to help secure the Hurricane nuts, not JB Weld.

Dacron speaker cabinet acoustic insulation was discarded and replaced with 2" egg crate foam.

HUGE MISTAKE!!! You just ruined the speakers.