SDA CRS impedance 6.7 ohms, not 3.7

network23

Hello,

I have two pair of polk SDA CRS speakers. 3 of them are showing 3.7ohms, but one is showing 6.7 ohms. (DC at the posts with a digital multimeter.)

On the one with 6.7 ohms I pulled one lead off of each driver and measured both mid/woof and the tweeter. The mid/woofs were 3.7 and the tweeter was 3.9.

I pulled the bottom crossover and nothing looks popped or burned, no bad smell inside.

The manual says these are supposed to be 6 ohms.

Can anyone explain what is going on?

Thanks

F1nut

You are measuring resistance, not the nominal impedance, which you can't do with a DVOM. As to why one speaker's resistance measures higher......you have some testing to do as something isn't right.

network23

You are right. Thanks for the correction. I have always refered to resistance as DC impedence.

Anyway, yes, I know something is not right. So how do I found out what is wrong?

Thanks.

bmbguy

First, see if you can locate the correct schematic for your speakers here:
http://www.polkaudio.com/forums/showthread.php?55888-POLK-AUDIO-Speaker-Wiring-Schematics-amp-More-Stereo-Dimensional-Array(SDA)

Then put your ohmmeter back to work, and see if the measurements of the 'bad' speaker's network make sense -- or compare a 'good' speaker's network to the 'bad' one to see if you can isolate where the difference is. For DC measurements, capacitors should appear as open circuits, inductors should appear as (very near) short circuits.

[Deleted User]

Hello,
Here is an SDA troubleshooting guide as post #9 in this sticky:
http://www.polkaudio.com/forums/showthread.php?55888-POLK-AUDIO-Speaker-Wiring-Schematics-amp-More-Stereo-Dimensional-Array(SDA)
Regards, Ken

network23

EDIT: I didn't get to the #9 post with the guide before posting. Sorry, I'm reading now.

While the schematics are helpful, I don't have the equipment to test the individual components. And the capacitors should not effect the DC impedence (sorry, resistance) unless they are just shorted out. And the inductors should never effect DC really. Not that much anyway.

Is there something that is common that goes bad?

and what is the "safetyguard" thing?

bmbguy

That is the (in)famous polyswitch for tweeter protection, a 'fuse' that resets itself after 'blowing'. You can find plenty of discussion on that device in this forum. Its resistance should measure somewhere around a half-ohm.

Even without the equipment to test the individual components, having the schematic and a 'working' model should allow you to isolate where the extra 3 ohms are showing up.

DarqueKnight

network23 wrote: »

Hello,

I have two pair of polk SDA CRS speakers. 3 of them are showing 3.7ohms, but one is showing 6.7 ohms. (DC at the posts with a digital multimeter.)

On the one with 6.7 ohms I pulled one lead off of each driver and measured both mid/woof and the tweeter. The mid/woofs were 3.7 and the tweeter was 3.9.

I pulled the bottom crossover and nothing looks popped or burned, no bad smell inside.

The manual says these are supposed to be 6 ohms.

Can anyone explain what is going on?

Thanks

Do you have the original CRS with two tweeters per cabinet or the CRS+ with one tweeter per cabinet? I am thinking you have the original CRS with the two SL1000 tweeters since the SL2000 has a much higher DCR than 3.9 ohms.

If you have a cracked (open) solder joint somewhere in the crossover, it could cause higher DCR readings at the binding post terminals. One way to be sure is to swap crossover boards.

You could also have a damaged component on the board. Electrical damage is not always apparent by sight or smell.

network23

DarqueKnight wrote: »

Do you have the original CRS with two tweeters per cabinet or the CRS+ with one tweeter per cabinet? I am thinking you have the original CRS with the two SL1000 tweeters since the SL2000 has a much higher DCR than 3.9 ohms.

If you have a cracked (open) solder joint somewhere in the crossover, it could cause higher DCR readings at the binding post terminals. One way to be sure is to swap crossover boards.

You could also have a damaged component on the board. Electrical damage is not always apparent by sight or smell.

I have the ones with 1 tweeter / spk. I have always referred to these as the CRS+

I'm going to go thru the toubleshoting page to see if I can find the problem. Thanks

network23

Okay, I went thru the troubleshooting guide and at first I thought it would be a great help. But after I went thru it all and started testing the speaker, I found there were several charts of data for the same speakers over and over with no identification as to what version of the speaker it applied to. NONE of them matched what my speaker tested. One was more or less close with "INF" or open circuits matching what the spec called for, but those that showed values did not match my speaker by a very large margin.

The speaker plays, plays correctly, it's just the dc impedance does not match any of the other speakers. All SDA CRS speakers are the single tweeter type, but the serial numbers are all over the place. Since the specs chart shows so many variants of the speakers if it possible Polk made a 6 ohm version? The manual show it's supposed to be 6 ohms DC resistance. So where do people get the idea it's a 4 ohm speaker?

Thanks

[Deleted User]

Hello,
The only components that could be adding the "extra" 3 Ohms would be either the voice coils of the 6.5" drivers, the series inductors or the connecting wires themselves (probably least likely). You mentioned that you had removed the two 6.5" drivers and measured the DC resistance and they were around 3.7 Ohms the only part left (assuming the wiring isn't wrong) are the series inductors. While they may look fine, there could be some problem not seen. Are all internal connections look correct? Are you able to take a photo of the inside of the cabinet, showing as much of the crossover as possible?
Regards, Ken

jimbo1421

network23 wrote: »

Since the specs chart shows so many variants of the speakers...

Since you have the CRS+, which chart you use depends on which interconnect you have, pin/blade (page 4) or blade/blade (page 5).

Jim

bmbguy

Kenneth Swauger wrote: »

Hello,
The only components that could be adding the "extra" 3 Ohms would be either the voice coils of the 6.5" drivers, the series inductors or the connecting wires themselves (probably least likely).

Assuming all solder joints and wiring connections are intact...

[Deleted User]

Hence the question: "Are all the internal connections look(ing) correct?"

gimpod

network23 wrote: »

Hello,

I have two pair of polk SDA CRS speakers. 3 of them are showing 3.7ohms, but one is showing 6.7 ohms. (DC at the posts with a digital multimeter.)

On the one with 6.7 ohms I pulled one lead off of each driver and measured both mid/woof and the tweeter. The mid/woofs were 3.7 and the tweeter was 3.9.

I pulled the bottom crossover and nothing looks popped or burned, no bad smell inside.

The manual says these are supposed to be 6 ohms.

Can anyone explain what is going on?

Thanks

To the OP, Your really not giving us enough info on which CRS+ you have to help out. Polk made 3 versions of the CRS+. From your description it sounds like you've got the 1986 Blade/blade Dual Board crossover version.

Year, Tweeter, Stereo Driver, Dim Driver, I.C., Crossover
1986, SL 2000, MW 6510, MW 6510, Blade/blade, Dual Board
1987, SL 2000, MW 6503, MW 6511, Bin/blade, Single Board
1989, SL 2000, MW 6510, MW 6511, Bin/blade, Single Board

Here's what the drivers should read in DCR
MW 6503 6.54 Ohms
MW 6510 6.57 Ohms
MW 6511 3.13 Ohms

For the SL 2000 it should be around 7 Ohms if I recall correctly. I would check that tweeter against another one all so make sure you have the correct drivers for your CRS+. All so when you check the DCR of a driver or tweeter make sure it's completely disconnected.

network23

They are definitely blade/blade and the date on almost all the drivers is aug 26th 1986.

with all drivers unhooked, basically there is nothing but open circuits between the red and black and blade 1 and blade 2 connections.

Here are pix of the drivers and crossovers.

Hope someone sees something.

bmbguy

That kinda makes sense -- with the drivers removed, I think all of the DC paths would be blocked by caps if you're only checking at the binding posts. For instance, if the tweeter part of the circuit were isolated, it would always measure 'open' -- driver in or driver out -- because of the series capacitance. With the MWs removed, the shunt caps would block the DC.

But now you can check the polyswitch, resistors and inductors for continuity without the drivers interfering with the readings.

If I'm looking at the right schematic, that CRS+ looks like it's the same as the SDA 2A.

[Deleted User]

Thanks for taking the photos, nothing looks like a likely candidate. If you would like to remove the crossover and send it to me I'll check it out and correct the problem at no charge. When I worked in Polk's CS I repaired quite a few crossovers over the years. Send me a PM if you want.
Cheers, Ken

[Deleted User]

Another thing you could try would be to compare this speaker with the matching CRS+ that checks out correctly. You would have to remove the two 6.5" drivers from that cabinet and measure the following: DC resistance between the positive speaker terminal (the binding post on the rear of the cabinet)and each of the positive wire ends that connect to the two 6.5" drivers. Then measure from the negative speaker terminal and the two negative wire ends of the two 6.5" drivers. Then repeat this process for the speaker that has the higher resistance. What we are trying to do is measure the DC resistance of the three coils by following the three paths from input terminals to where the wires attach to the drivers themselves and comparing the two speakers.

bmbguy

Wild stab from across the internet guesses that one of the two MW paths could be open, and when the drivers are installed you're reading only one path instead of both in parallel. The tweeter, with its blocking cap, doesn't figure into the DC resistance test.

For a quick test, you could try connecting each MW separately on the 'bad' speaker and see what you read from the binding posts in each case. You might find one of them reads an open circuit.

[Deleted User]

His two photos show one driver with 5.9 Ohms and the other is 6.2 Ohms indicating that neither driver is open.

bmbguy

I know the drivers weren't open -- I said the 'paths' to the drivers. meaning connections, inductors, DC-wise. If one of those two paths is open, you would read just the other one alone -- which would be around 6-7 ohms probably.

[Deleted User]

Which is exactly why I recommended measuring the path from input terminals to ends of the wires that connect the two drivers and comparing this to the correct speaker. This would then provide whether the problem is with the "stereo" section of the LP network or the "SDA" section. If the problem were an open path to either of drivers then that driver wouldn't have functioned, but he has said that the speaker basically operates correctly.

bmbguy

Yeah, I just thought that if the SDA driver path were open, you might not be able to tell by listening as easily. And the numbers kinda make sense that one path is open. That's why I thought as long as he had the drivers out, he could connect them one at a time and check each the resistance of each path by itself before cracking open another speaker.

Whatever way to get there.

[Deleted User]

What I hope happens is that he measures both speakers and finds out that one of the three inductors has a higher DC resistance than what is supposed to be there. Then I can ask Kim in CS to send him the correct inductor or I hunt around in my box of left over Polk parts and send him the coil. But, we need to narrow down which area of the crossover is responsible and this should do it.

Toolfan66

Very nice offering Ken!!

Just another reason this place is the best!!!

Peace be with you and yours..

network23

Thank you all for the posts, suggestions and especially Ken for the offer to fix it. I'm going to reread your suggestions and see what I can come up with. I'll post a little bit later what I find.

One thing is that in the trouble shooting manual, it says to do the testing with the speakers disco'd. Based on your posts above, that would then be measuring the inductors and paths only, right?

bmbguy

network23 wrote: »

One thing is that in the trouble shooting manual, it says to do the testing with the speakers disco'd. Based on your posts above, that would then be measuring the inductors and paths only, right?

I'm pretty sure the troubleshooting guide means you should have the cables disconnected from the amplifier and the SDA cable disconnected - but it's intended that the measurements be done with the drivers connected to the crossovers. So the driver voice coils would also be included in the measurements.

network23

Okay, I found the problem! One of the wires on the bottom crossover while it was on the tab, the connection was very loose. The spade connector was "sprung." Ie, it was pushed on, but there was not enough friction to make a good connection. I was testing all paths and had to turn the speaker up on it's end to make it easier to test from front to back. When I did that, the black wire simply fell off the connection. I went to put it back on and it just slide on and off with no effort at all. So took a pair of needle nose pliers and crimped it down a bit and put it back on the connector. It's now a nice firm connection. I tested the DCR and it's 3.8 now just like the rest of the speakers. Hooked it up and played some Dire Straights and it's great again.

So we now have both pair working again. Now I have to look into the polyswitch mod.

network23

BTW, now that we have this problem solved, you can see what my plans are here:

http://www.polkaudio.com/forums/showthread.php?132891-Quad-SDA-CRS-Project

Thanks for the help.

bmbguy

Glad to hear you found the problem! And better yet - it was an 'easy fix', as they say.