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Bad capacitor? AV-1 trouble shooting


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21 replies to this topic

#1 of 22 OFFLINE   Jonathan Lofgren

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Posted June 24 2004 - 09:54 AM

Hello,
I built a pair of GR-research AV-1s and it turned out that one of the tweeters wasn't working. I actually didn't notice it for awhile because I had kind of funny speaker placement and the working tweeter was closer to me. This was the first time I'd tried building speakers, and the first time I'd even soldered. Anyway, I've figured it out now and I've gotten inside the speaker.

I measured with a multimeter and started at the wire where the tweeter connects. It didn't register so my tweeter is alright (although I might have messed it up trying to get de-solder, more on that later). Then I worked backward until I got a reading. It turns out that on one lead of a capacitor a get a range of 50-200 mA, and on the other I get nothing. I assume this means that my capacitor is bad. Also, now I guess I have de-solder a little bit and get the capacitor out. How do you de-solder? I just tried heating the solder with a soldering iron, like when I put it together. That clearly didn't work because I didn't have a good way to remove the solder.

Is my capacitor bad, and any tips on de-soldering? Thank you in advance for any and all replies.
"One trouble with books is that they're not so thoroughly safeguarded by intelligent censors as the movies are, and when you drop into the library and take out a book you never know what you're wasting your time on."
Sinclair Lewis Mainstreet

#2 of 22 OFFLINE   Mitch N

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Posted June 24 2004 - 10:17 AM

You can desolder with a vacuum type device or with desoldering braid. Both can be found at your local radio shack. To use the braid, you need to have a decent and hot iron. 20w pencils need not apply.

#3 of 22 OFFLINE   Jonathan Lofgren

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Posted June 24 2004 - 12:40 PM

Thanks! What are the advantages/disadvantages of suction versus the braid?
"One trouble with books is that they're not so thoroughly safeguarded by intelligent censors as the movies are, and when you drop into the library and take out a book you never know what you're wasting your time on."
Sinclair Lewis Mainstreet

#4 of 22 OFFLINE   ThomasW

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Posted June 24 2004 - 01:32 PM

Quote:
What are the advantages/disadvantages of suction versus the braid?

Spend a few bucks and you'll know.

RadioShack Desoldering tools

#5 of 22 OFFLINE   Michael R Price

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Posted June 24 2004 - 01:50 PM

Johnathan,

You said you measured at the place the tweeter connects and did not get a resistance reading. Do you mean before or after the crossover? If that was after the crossover, I would expect a DC resistance of around 6 ohms. If the tweeter itself has a different resistance, there might be something wrong with it.

I would buy the "desoldering iron" which is the little soldering iron like thing with a red squishy bulb attached to it. It works, but over time it gets clogged up and I'm not sure how to fix that.

#6 of 22 OFFLINE   Jonathan Lofgren

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Posted June 24 2004 - 09:54 AM

Hello,
I built a pair of GR-research AV-1s and it turned out that one of the tweeters wasn't working. I actually didn't notice it for awhile because I had kind of funny speaker placement and the working tweeter was closer to me. This was the first time I'd tried building speakers, and the first time I'd even soldered. Anyway, I've figured it out now and I've gotten inside the speaker.

I measured with a multimeter and started at the wire where the tweeter connects. It didn't register so my tweeter is alright (although I might have messed it up trying to get de-solder, more on that later). Then I worked backward until I got a reading. It turns out that on one lead of a capacitor a get a range of 50-200 mA, and on the other I get nothing. I assume this means that my capacitor is bad. Also, now I guess I have de-solder a little bit and get the capacitor out. How do you de-solder? I just tried heating the solder with a soldering iron, like when I put it together. That clearly didn't work because I didn't have a good way to remove the solder.

Is my capacitor bad, and any tips on de-soldering? Thank you in advance for any and all replies.
"One trouble with books is that they're not so thoroughly safeguarded by intelligent censors as the movies are, and when you drop into the library and take out a book you never know what you're wasting your time on."
Sinclair Lewis Mainstreet

#7 of 22 OFFLINE   Mitch N

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Posted June 24 2004 - 10:17 AM

You can desolder with a vacuum type device or with desoldering braid. Both can be found at your local radio shack. To use the braid, you need to have a decent and hot iron. 20w pencils need not apply.

#8 of 22 OFFLINE   Jonathan Lofgren

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Posted June 24 2004 - 12:40 PM

Thanks! What are the advantages/disadvantages of suction versus the braid?
"One trouble with books is that they're not so thoroughly safeguarded by intelligent censors as the movies are, and when you drop into the library and take out a book you never know what you're wasting your time on."
Sinclair Lewis Mainstreet

#9 of 22 OFFLINE   ThomasW

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Posted June 24 2004 - 01:32 PM

Quote:
What are the advantages/disadvantages of suction versus the braid?

Spend a few bucks and you'll know.

RadioShack Desoldering tools

#10 of 22 OFFLINE   Michael R Price

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Posted June 24 2004 - 01:50 PM

Johnathan,

You said you measured at the place the tweeter connects and did not get a resistance reading. Do you mean before or after the crossover? If that was after the crossover, I would expect a DC resistance of around 6 ohms. If the tweeter itself has a different resistance, there might be something wrong with it.

I would buy the "desoldering iron" which is the little soldering iron like thing with a red squishy bulb attached to it. It works, but over time it gets clogged up and I'm not sure how to fix that.

#11 of 22 OFFLINE   Robert Garrison

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Posted June 25 2004 - 02:17 AM

What you should do is learn how to use the braid. It's not hard and is quick enough. The part about needing a 20w iron, well maybe, that depends on the job. You can get braid at parts express. Search for "solder braid" The .10" wide should work nicely. This page discusses briefly how to use it: Google "how to use braid desolder"

About the tweeter. You might get weird readings if leave the crossover connected. To test if the tweeter coil isn't destroyed you can simply measure it's DC resistance. It should be within close to its stated AC impedence. Since your desoldering anyway, might be a good idea to install 1/4" disconnects to your leads. Parts Express, search for part number "095-272" 1/4" should be the right size.

Sorry but I wasn't allowed to post with URLs.

--Have fun

#12 of 22 OFFLINE   Brian Fellmeth

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Posted June 25 2004 - 02:58 AM

Hold on there babalui. You have not proven that the cap is bad. It seems like you are useing your meter to measure voltage or current at various points with a signal present- not sure if your measuring AC or DC. If your meter is set to DC, then its normal for there to be a loss of voltage across a capacitor. Blocking DC is one of the things a capacitor does.

Your problem is probably a bad solder joint. Investigate this with the meter set to measure resistance. Resistance across capacitors is infinity, and inductors is <1 ohm. Redraw the schematic replacing caps with open and inductors with shorts. This will leave a very simple "DC" version of your crossover. Then, measure the resistance between various points in the crossover till you find the bad joint. Do this without an amp hooked up.

Also, you can test the tweeter by bypassing the crossover and sending it a full range signal ON VERY LOW VOLUME- just to confirm that it is functioning. The problem with robert's suggestion is that the tweeter could be nonfunctioning yet still have normal voice coil resistance.

#13 of 22 OFFLINE   Hank Frankenberg

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Posted June 25 2004 - 01:57 PM

My guess would be that your inexperience in soldering has resulted in heat applied too long to a tweeter terminal, resulting in melting the voice coil lead to the terminal. The wire in a tweeter voice coil is VERY fine guage wire, and if you can open the tweeter without ruining it, I bet you'll find one of the V.C. leads is "open", and looks like the fine guage wire inside a small amp fuse that has melted and "opened".

#14 of 22 OFFLINE   Jonathan Lofgren

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Posted June 25 2004 - 03:51 PM

Thank you all for your replies. I'm sure that my poor soldering has caused trouble, but I did put the speaker wire to just the tweeter terminals and the tweeter played so I assume that it's alright.

As for the measuring, I hooked the speaker wire to the binding posts and played music at a low volume. Then I measured DC in Amperes. The reason that I assumed it was the capacitor is because I got a reading while touching one part of the capacitor's cable, but not on the other side. I'm not sure what the right words are, but the capacitor has a little bit of wire sticking out of both sides. When I touched my multimeter to one side of the capacitors wire, I got a measurement. When I touched the other side of the capacitor's wire, I got nothing.
"One trouble with books is that they're not so thoroughly safeguarded by intelligent censors as the movies are, and when you drop into the library and take out a book you never know what you're wasting your time on."
Sinclair Lewis Mainstreet

#15 of 22 OFFLINE   Jonathan Lofgren

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Posted June 25 2004 - 04:27 PM

Brian,
First, thanks for your reply. I definitely appreciate it. I've read your reply a couple of times and I'm not quite sure that I understand what you're saying.

>>Resistance across capacitors is infinity, and inductors is <1 ohm. Redraw the schematic replacing caps with open and inductors with shorts. This will leave a very simple "DC" version of your crossover. Then, measure the resistance between various points in the crossover till you find the bad joint. Do this without an amp hooked up.<<

I'm not sure what you mean when you say to re-draw the schematic. You mean that caps become 1 and inductors become 0, then I poke around until I get a reading of 1 that should be a 0?

Again, I appreciate the help.
"One trouble with books is that they're not so thoroughly safeguarded by intelligent censors as the movies are, and when you drop into the library and take out a book you never know what you're wasting your time on."
Sinclair Lewis Mainstreet

#16 of 22 OFFLINE   Robert Garrison

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Posted June 25 2004 - 05:02 PM

I'm glad your tweeter at least has some sound. Let's hope it is the intended sound. Capacitors only work when they are given an AC signal. They will work briefly with a DC resistance meter until one plate charges up then it blocks DC current flow. So when you initially hook up a capacitor to the meter you should see some digits flick for a second or two while the DC resistance climbs to infinity (It's been a while since I've done a measurement like that).

Since I cannot see who posted it at this point, I give credit to said it first. The poster was trying to say that with a DC resistance meter you will see very low resistance on an inductor and high (infinite) in the capacitor. If you do however get a non-infinite number, i.e a very low number then you may have a shorted capacitor. If you happen to have a capacitance meter you could check to make sure your caps are'nt open either.

#17 of 22 OFFLINE   Cary_H

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Posted June 25 2004 - 11:37 PM

Hold on a sec.
Jonathan.....I'm not sure why at this point current is even a concern. Does your meter even have a clamp? If you're using the meter's probes to register current you'll need them in series with the circuit closed and powered up.

If you're trying to find what's keeping your circuit open check for continuity...being referred to here as resistance. If you have continuity between two terminals you'll get a reading. If the circuit between your two points is open, you'll see a reading of 0, or OL.(open line)
To check for continuity you can't do it between two points on a closed circuit. The line between your two points might be open, but if the backside of the circuit is still tied in and closed, you could be fooled into thinking what you're testing is OK when it's really seeing the backside's continuity.
Using de-soldering braid is a no brainer.

#18 of 22 OFFLINE   Brian Fellmeth

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Posted June 26 2004 - 03:04 AM

First, do not trouble shoot using a meter on a live circuit, especially with the meter set to measure current. It would be very easy to create a short across your speaker terminals and damage the amp. Instead, investigate with the speaker unhooked and the meter set to measure ohms (resistance). In this mode, your meter uses its battery to try to send DC current between the leads abd tells you how hard the components you are measureing is fighting the flow of current. A capacitor will allow a very brief burst of current then act like a broken wire- infinite DC resistance. A coil puts up trivial resistance, less than 1 ohm. A resister puts up the amount of resistance it is rated to do.

Now, measure the resistance across the tweeter lugs- should be somewhere between 2 and 8 ohms. Then pick a lug and attach lead there. Then with the other lead, work back in the circuit towards the speaker terminal. The modified schematic will tell you what the reisistance should be at each point. Coils are same as wires, caps are the same as broken wires, resisters are whatever they are. Hopefully, you will find 2 points with infinite resistance that should have sinite resistance, and your bad solder joint will be betweem these 2 points.

Plan b. Do you have any wires with alligator clips at each end ? If not, get some next time at radioshack. Pick a cap in the tweeter circuit and put a clip on both cap leads- turning the cap into a short- eliminating it from the circuit. Then play the speaker (AT VERY LOW VOLUME) and see if the tweeter now plays. (may want do disconnect woofer to make it easier to tell if tweeter is playing) If so, then bad cap.

Plan c- can you fax or email your schematic ? Fax # (916) 863 1427

#19 of 22 OFFLINE   Danny Richie

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Posted June 26 2004 - 03:54 AM

Not to take away from the fun of doing it yourself, but if all else fails just send it to GR Research.

I have a feeling they will diagnose the problem and correct whatever is wrong with it for you free of charge.

#20 of 22 OFFLINE   Michael R Price

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Posted June 26 2004 - 09:46 AM

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