RTi4 crossovers

toolbelt

One of my units suddenly stopped working completely, almost like it blew a fuse. I confirmed its a speaker issue by swapping speakers. I checked all connections, cleaned all terminals etc but no go. I use these mainly for watching tv at relatively low volume. The crossover has capacitors and resistors, etc, however some of these are dedicated for feeding either the tweeter or midrange only (but not both), so I'm wondering if anybody knows which electrical components feed a signal to BOTH speakers, as I have no sound at all. I checked continuity for the signal in and everything is good. There are white resistors marked 5W 2R5(ohm)J and 5W 3R3(ohm)J and I'm getting zero reading at the latter one's leads. Do components need to be removed from the board to take readings or can I measure them in place? Any help appreciated.

F1nut

You would need to lift one resistor lead at a minimum to get an accurate reading. That said, do either of the resistors look burnt and/or cracked?

Pics always help.

toolbelt

Looking carefully at the one resistor (which are like white ceramic blocks), it looks very slightly discolored compared to the other one, and that is the one I'm getting no reading on (while measuring it in place).

toolbelt

This is the backside of those two resistors for comparison.

Gardenstater

You're not getting any sound out of the midwoofer or the tweeter? That 2.5Ohm resistor does definitely looked burnt. I don't see the schematic in the archives. Doesn't look like there are any fuses or polyswitches.

What do you get when you take an ohm reading from the pos to neg binding post, on both the good speaker and the bad one?

toolbelt

As I've pulled the crossover out of the one unit, would I need to reassemble the speaker to run that comparison? And yes, no sound out of either the tweeter or woofer/midrange. That's why I'm thinking it has to be a component that is common to both. Would any resistor or capacitor feed both speakers?

Gardenstater

If it is a typical 2nd order crossover, there wouldn't be any components in common. But who knows, there might be a resistor in common; that bad one.

Check the resistance of the midwoofer and the tweeter. Hopefully neither are blown.

toolbelt

I'm getting no resistance reading on the individual speakers, however don't those terminals have no continuity and therefore no resistance to measure?

Gardenstater

I would expect you would get something around 6 ohms. Are you getting infinite = open or are you getting 0 = shorted?

Capacitors have no DC continuity but coils do; both inductors and voice coils in loudspeakers. Try the drivers in the good speaker and see what resistance you get.

toolbelt

I'm getting no reading at all, like I'm testing air, on both. The speaker was fine (tweeter and woofer) until both stopped working 2 days ago, hence why I suspected a connection or bad capacitor/resistor. I have to assume one of those components feeds both speakers (directly/indirectly) and failed suddenly. Other than that one slightly discolored resistor which is producing no reading (while mounted to the board), nothing is jumping out at me. These crossovers are a pain to deal with as the binding post backplate is not easy to remove to get a good look at the back of the circuit board itself. The binding posts are bolted through the whole works and held by nuts wedged between them. I was able to grab the nut and spin out the binding posts, as there's no wrench that could access and turn the nuts. Even pulling out the speakers is a pain as there is about an inch of play in the wires.

Gardenstater

If you are getting infinite resistance on both drivers then they are both blown. Whatever event caused the resistor to overheat and burn out also fried both of the drivers. I'd suspect your amplifier.

toolbelt

I tried hooking up the speaker wire directly to the individual speakers (bypassing the crossover) and got no sound from either. To be sure, I'll try swapping the speakers with my working unit to see if the speakers themselves are the problem. As mentioned, I use them mainly as tv monitors at relatively low volume, and the AV receiver is putting out a clean signal to all channels. I suppose anything is possible at this point. I'm curious if the crossover capacitors boost the signal to fire the magnets, in which case my bypass test was an effort in futility. I know an AC compressor wont fire without a capacitor to get it started. I've never had a speaker wear out so this is all new to me. I may have to take my Cerwin Vega U12's out of mothballs as I know they still work since 1979. lol

Gardenstater

Again, all I can say is I'd be worried about that channel in that amplifier. I'm sure it puts out clean power but that is when it hasn't malfunctioned. Did you have any electrical storms? Was the speaker playing when it failed or did it just not produce sound when you turned the amp on? Crossover components don't fry drivers, amplifiers do.

toolbelt

I pretty well use them daily, and then 2 days ago, the sound seemed off when I first turned the system on, at which time I realized the right speaker wasn't putting out sound. I switched right and left speakers to test the amp/wiring out and the left speaker has been connected to the righthand channel ever since, with no issues. The right speaker has no output regardless of which channel I use. As mentioned, if I swap the individual speakers tomorrow and the RH units put out sound, we can isolate it to a bad crossover. I can either try replacing that bad? resistor, or perhaps I should just get new crossovers for both units. Obviously Polk won't have them, so I may try other brands from Amazon, etc or maybe it's time to just get new bookshelf speakers as they're relatively cheap for the quality I would need.

ChrisD06

toolbelt wrote: »

I tried hooking up the speaker wire directly to the individual speakers (bypassing the crossover) and got no sound from either. To be sure, I'll try swapping the speakers with my working unit to see if the speakers themselves are the problem. As mentioned, I use them mainly as tv monitors at relatively low volume, and the AV receiver is putting out a clean signal to all channels. I suppose anything is possible at this point. I'm curious if the crossover capacitors boost the signal to fire the magnets, in which case my bypass test was an effort in futility. I know an AC compressor wont fire without a capacitor to get it started. I've never had a speaker wear out so this is all new to me. I may have to take my Cerwin Vega U12's out of mothballs as I know they still work since 1979. lol

The speaker wire directly to the driver should yield sound. Hooking it up into the other crossover is just going to yield no sound but in a more time-consuming way.

Could you send a photo of the bottom of the crossover board? I'm curious what the trace layout is...

Gardenstater

Well again, I think that your amp had a temporary malfunction in that channel that fried both that resistor and the drivers in the speaker. Blaming the crossover would be like shooting the messenger. I don't think that resistor failing caused both the tweeter and the midwoofer to fail. I doubt that resistor is even in the midwoofer circuit but not sure without the schematic or the crossover to look at.

ChrisD06

Gardenstater wrote: »

I doubt that resistor is even in the midwoofer circuit but not sure without the schematic or the crossover to look at.

I don't think I've seen a Polk schematic where there is a shared resistor between both drivers however if BOTH drivers suddenly crapped out, I wouldn't be surprised if the other resistor is dead too and just isn't showing it visibly. His amp is most definitely the culprit.

toolbelt

I will be disassembling the crossover board from the crossover assembly tomorrow and will post some pics. The bottom of the board faces the back of the bind post cover with very little space between them.

ChrisD06

toolbelt wrote: »

I will be disassembling the crossover board from the crossover assembly tomorrow and will post some pics. The bottom of the board faces the back of the bind post cover with very little space between them.

Yeah if you can just send a photo of the trace side tomorrow that'd be awesome. Those wires from the binding posts are quite short IIRC so you might need to desolder them.

toolbelt

[quote= I wouldn't be surprised if the other resistor is dead too and just isn't showing it visibly. His amp is most definitely the culprit.[/quote]

The resistance checks out on the other resistor. I can also try out a 9v battery to see if the coils move. Would that rule out a bad driver semi sorta?

ChrisD06

toolbelt wrote: »

The resistance checks out on the other resistor. I can also try out a 9v battery to see if the coils move. Would that rule out a bad driver semi sorta?

You can do this as well, yes. Surprised the resistance checks out... either way I'd replace both if you decide to repair these (you should!)

Gardenstater

A 9V battery on the midwoofer (AA for tweeter) would be a good test for functionality but in this case it is redundant because didn't you say that there is no continuity in the voice coil when you test with an ohmmeter?

toolbelt

Just saw a listing for a pair of 8 month old Polk XT15's for $125 Cdn. That might solve the problem? lol

Gardenstater

Maybe but only until the next time your amp pukes I would consider fuses until you can get the amp checked out by a service tech, especially at turn on. Maybe unplug the amp when not in use as well in case you are having electrical supply problems or electrical storm damage.

toolbelt

Gardenstater wrote: »

A 9V battery on the midwoofer (AA for tweeter) would be a good test for functionality but in this case it is redundant because didn't you say that there is no continuity in the voice coil when you test with an ohmmeter?

Yes I tested and had no continuity on both individual speaker terminals. If I had a 9v handy it could help. I'll dig one up tomorrow and test just for the sake of it.

ChrisD06

toolbelt wrote: »

Just saw a listing for a pair of 8 month old Polk XT15's for $125 Cdn. That might solve the problem? lol

The ones in Mississauga?

Also- Hello there, fellow Canadian!

toolbelt

ChrisD06 wrote: »

toolbelt wrote: »

Just saw a listing for a pair of 8 month old Polk XT15's for $125 Cdn. That might solve the problem? lol

The ones in Mississauga?

Also- Hello there, fellow Canadian!

Damn are you going to start a bidding war? lol

ChrisD06

toolbelt wrote: »

ChrisD06 wrote: »

toolbelt wrote: »

Just saw a listing for a pair of 8 month old Polk XT15's for $125 Cdn. That might solve the problem? lol

The ones in Mississauga?

Also- Hello there, fellow Canadian!

Damn are you going to start a bidding war? lol

Nah, I'm in Nova Scotia. I just browse Kijiji through all of Canada incase a cool Polk item pops up like those RT35s I shipped from Toronto.

They're all yours!

toolbelt

Was it an empty box containing a brick? lol

ChrisD06

toolbelt wrote: »

Was it an empty box containing a brick? lol

No! It actually wasn't! First time I tried to ship something from Kijiji I got scammed for $65 (he claimed he had a PSW650, I fell for the scam and I was too excited about the potential to quickly notice the red flags). This time he actually shipped 2 mint condition RT35s. I paid $50 for shipping and $60 for the speakers, they arrived in 2 days! I also bought an MW7011 for one of my RT35s which fell off the wall and that arrived packed very nicely from a private audio dealer (I have 4 RT35s).

So that's 2 for 3 in terms of good Kijiji shipping experiences LOL

toolbelt

Ive had unbelievable good luck with kijiji even though I'm the doubting thomas type. Mind you, I've always inspected the goods in person. mostly automotive related stuff or tools. Those XT15's seem like a suitable replacement provided they're not blown. I don't care about the mfg warranty in any case.