A couple days ago I was near one of my Dahlquist DQ-10s when I heard
something funny. It sounded like a low-level intermittent connection. It had
that unmistakable local character--definitely not program material--and
seemed to be coming from the midrange driver (I later learned that this unit
is called the midbass in this five-driver system). I rotated the treble
control on the rear of the speaker cabinet, thinking a dirty pot might be
responsible (even though this alters the level of another driver). By
that point the intermittent sound had stopped. It seemed that nothing at all
was coming from the driver. I removed the rear screen, and with an ohmmeter
determined that the voice coil was open.

I unmounted the driver and examined it. It looked perfect. I bounced it
around a bit and once briefly managed to read about 60 ohms across the voice
coil, but basically it was dead. I remembered that years earlier I had once
popped the 3-amp fuse in that speaker. I couldn't recall the circumstances,
but I figured the voice coil probably had blown at that time.

The strange thing is that I hadn't noticed anything amiss with the sound,
and I remembered that the mono sound image was always properly centered. I
checked the other speaker, and sure enough, its midbass was open too. I
played some familiar music and everything sounded normal. So much for my
ears!

Although I hadn't sat down and listened seriously to my system in a long
time, since buying my DQ-10s new in the early 1980s I had always loved them.
I was pretty sad about having blown them up. After checking on the Internet,
I learned that this particular driver had not been manufactured in a long
time and was now unavailable. Bummer. One place said they could rebuild
them. I sent an e-mail asking how much it would cost, but after seeing what
they charged for other drivers, I knew I wouldn't be willing to spend the
hundreds they were likely to ask to repair a pair. Other sites offered
replacement drivers, but I was very skeptical that the properties would be
similar enough to the original drivers. If only I had just one working
driver to measure a few parameters. Then I might be able to select a
reasonable replacement. I didn't even know the impedance.

The next morning I considered opening up the drivers and attempting to fix
the voice coil myself. I had never done anything like that, but I figured
the drivers were useless the way they were, so why not give it a try. Then I
started thinking about the probable failure mechanism. I assumed that I had
overheated the voice coil wire and melted it in one spot. Since the current
stops as soon as a break occurs, I figured the gap between the broken
segments was likely to be quite small.

I wondered whether I might apply a high voltage, bridge the gap with an arc,
and remelt the wire ends together. It was worth a shot. I charged a 47 uF
capacitor to 100 volts and touched it to the driver terminals. There was a
loud whomp that scared the **** out of me. Then I realized that it was just
the cone responding to the current impulse, which meant I had continuity.
The voice coil measured 6.8 ohms! I connected the driver to a little
push-pull 6V6 amp I had nearby. What a relief--it sounded perfectly normal!
I turned the volume up to clipping (12 watts) for a short while and the
driver continued to work. At least it was able to handle more than flea
power, though for how long I didn't know.

I zapped the other blown driver. Whomp! and 7.1 ohms. It too sounded fine.

I made a few simple measurements on the drivers and then reinstalled them in
the DQ-10s. They worked fine. I kept the volume down at first, but the
drivers continued to work. After several hours I gathered my courage and
turned things up to a perfectly satisfying listening level (loud, but not
super loud). The drivers kept working, and are still working two days later.
I've replaced the 3-amp speaker fuses with 2-amp units, and I don't intend
ever crank the system up really loud. But I'm very happy to have my
DQ-10s back.

Incidentally, I don't notice any difference in sound now that the midbass
units are functioning. This may be partly due to the narrow 400-1000 Hz
range the drivers operate in and the first-order crossover that allows the
adjacent-frequency drivers to emit a fair amount of power in this passband.
But I think it's mostly due to my lack of listening acuity.

I don't know whether this driver revival will last. It's hard to believe
that a spark can make a reliable weld. But perhaps the break was not in the
voice coil itself. Maybe the solder joining the stranded leads to the voice
coil wire had melted, and the spark simply did a remelt. This might have a
better long-term chance of survival. These junctions are not visible on the
midbass unit as they are on the surface of the woofer cone.

Even if this fix doesn't last, at least it revived the drivers long enough
that I could make some measurements. If I ever do need to get some
replacements, I'll have a better idea what to look for.

Brian

(Brian) wrote in
om:

A couple days ago I was near one of my Dahlquist DQ-10s when I heard
something funny. It sounded like a low-level intermittent connection. It
had
that unmistakable local character--definitely not program material--and
seemed to be coming from the midrange driver (I later learned that this
unit
is called the midbass in this five-driver system). I rotated the treble
control on the rear of the speaker cabinet, thinking a dirty pot might
be
responsible (even though this alters the level of another driver). By
that point the intermittent sound had stopped. It seemed that nothing at
all
was coming from the driver. I removed the rear screen, and with an
ohmmeter
determined that the voice coil was open.

I unmounted the driver and examined it. It looked perfect. I bounced it
around a bit and once briefly managed to read about 60 ohms across the
voice
coil, but basically it was dead. I remembered that years earlier I had
once
popped the 3-amp fuse in that speaker. I couldn't recall the
circumstances,
but I figured the voice coil probably had blown at that time.

The strange thing is that I hadn't noticed anything amiss with the
sound,
and I remembered that the mono sound image was always properly centered.
I
checked the other speaker, and sure enough, its midbass was open too. I
played some familiar music and everything sounded normal. So much for my
ears!

Although I hadn't sat down and listened seriously to my system in a long
time, since buying my DQ-10s new in the early 1980s I had always loved
them.
I was pretty sad about having blown them up. After checking on the
Internet,
I learned that this particular driver had not been manufactured in a
long
time and was now unavailable. Bummer. One place said they could rebuild
them. I sent an e-mail asking how much it would cost, but after seeing
what
they charged for other drivers, I knew I wouldn't be willing to spend
the
hundreds they were likely to ask to repair a pair. Other sites offered
replacement drivers, but I was very skeptical that the properties would
be
similar enough to the original drivers. If only I had just one working
driver to measure a few parameters. Then I might be able to select a
reasonable replacement. I didn't even know the impedance.

The next morning I considered opening up the drivers and attempting to
fix
the voice coil myself. I had never done anything like that, but I
figured
the drivers were useless the way they were, so why not give it a try.
Then I
started thinking about the probable failure mechanism. I assumed that I
had
overheated the voice coil wire and melted it in one spot. Since the
current
stops as soon as a break occurs, I figured the gap between the broken
segments was likely to be quite small.

I wondered whether I might apply a high voltage, bridge the gap with an
arc,
and remelt the wire ends together. It was worth a shot. I charged a 47
uF
capacitor to 100 volts and touched it to the driver terminals. There was
a
loud whomp that scared the **** out of me. Then I realized that it was
just
the cone responding to the current impulse, which meant I had
continuity.
The voice coil measured 6.8 ohms! I connected the driver to a little
push-pull 6V6 amp I had nearby. What a relief--it sounded perfectly
normal!
I turned the volume up to clipping (12 watts) for a short while and the
driver continued to work. At least it was able to handle more than flea
power, though for how long I didn't know.

I zapped the other blown driver. Whomp! and 7.1 ohms. It too sounded
fine.

I made a few simple measurements on the drivers and then reinstalled
them in
the DQ-10s. They worked fine. I kept the volume down at first, but the
drivers continued to work. After several hours I gathered my courage and
turned things up to a perfectly satisfying listening level (loud, but
not
super loud). The drivers kept working, and are still working two days
later.
I've replaced the 3-amp speaker fuses with 2-amp units, and I don't
intend
ever crank the system up really loud. But I'm very happy to have my
DQ-10s back.

Incidentally, I don't notice any difference in sound now that the
midbass
units are functioning. This may be partly due to the narrow 400-1000 Hz
range the drivers operate in and the first-order crossover that allows
the
adjacent-frequency drivers to emit a fair amount of power in this
passband.
But I think it's mostly due to my lack of listening acuity.

I don't know whether this driver revival will last. It's hard to believe
that a spark can make a reliable weld. But perhaps the break was not in
the
voice coil itself. Maybe the solder joining the stranded leads to the
voice
coil wire had melted, and the spark simply did a remelt. This might have
a
better long-term chance of survival. These junctions are not visible on
the
midbass unit as they are on the surface of the woofer cone.

Even if this fix doesn't last, at least it revived the drivers long
enough
that I could make some measurements. If I ever do need to get some
replacements, I'll have a better idea what to look for.

Brian


Your assesment seems about right. The weld is certainly not a permanent
fix but stranger things that that have been known to happen so you might
luck out.

I would probably start shopping for some new speakers though. The DQ's
days are numbered.

r


--
Nothing beats the bandwidth of a station wagon filled with DLT tapes.

Interesting. Zapping something like that should widen the gap kinda the way
a fuse works.
John

"Brian" wrote in message
om...
A couple days ago I was near one of my Dahlquist DQ-10s when I heard
something funny. It sounded like a low-level intermittent connection. It
had
that unmistakable local character--definitely not program material--and
seemed to be coming from the midrange driver (I later learned that this
unit
is called the midbass in this five-driver system). I rotated the treble
control on the rear of the speaker cabinet, thinking a dirty pot might be
responsible (even though this alters the level of another driver). By
that point the intermittent sound had stopped. It seemed that nothing at
all
was coming from the driver. I removed the rear screen, and with an
ohmmeter
determined that the voice coil was open.

I unmounted the driver and examined it. It looked perfect. I bounced it
around a bit and once briefly managed to read about 60 ohms across the
voice
coil, but basically it was dead. I remembered that years earlier I had
once
popped the 3-amp fuse in that speaker. I couldn't recall the
circumstances,
but I figured the voice coil probably had blown at that time.

The strange thing is that I hadn't noticed anything amiss with the sound,
and I remembered that the mono sound image was always properly centered. I
checked the other speaker, and sure enough, its midbass was open too. I
played some familiar music and everything sounded normal. So much for my
ears!

Although I hadn't sat down and listened seriously to my system in a long
time, since buying my DQ-10s new in the early 1980s I had always loved
them.
I was pretty sad about having blown them up. After checking on the
Internet,
I learned that this particular driver had not been manufactured in a long
time and was now unavailable. Bummer. One place said they could rebuild
them. I sent an e-mail asking how much it would cost, but after seeing
what
they charged for other drivers, I knew I wouldn't be willing to spend the
hundreds they were likely to ask to repair a pair. Other sites offered
replacement drivers, but I was very skeptical that the properties would be
similar enough to the original drivers. If only I had just one working
driver to measure a few parameters. Then I might be able to select a
reasonable replacement. I didn't even know the impedance.

The next morning I considered opening up the drivers and attempting to fix
the voice coil myself. I had never done anything like that, but I figured
the drivers were useless the way they were, so why not give it a try. Then
I
started thinking about the probable failure mechanism. I assumed that I
had
overheated the voice coil wire and melted it in one spot. Since the
current
stops as soon as a break occurs, I figured the gap between the broken
segments was likely to be quite small.

I wondered whether I might apply a high voltage, bridge the gap with an
arc,
and remelt the wire ends together. It was worth a shot. I charged a 47 uF
capacitor to 100 volts and touched it to the driver terminals. There was a
loud whomp that scared the **** out of me. Then I realized that it was
just
the cone responding to the current impulse, which meant I had continuity.
The voice coil measured 6.8 ohms! I connected the driver to a little
push-pull 6V6 amp I had nearby. What a relief--it sounded perfectly
normal!
I turned the volume up to clipping (12 watts) for a short while and the
driver continued to work. At least it was able to handle more than flea
power, though for how long I didn't know.

I zapped the other blown driver. Whomp! and 7.1 ohms. It too sounded fine.

I made a few simple measurements on the drivers and then reinstalled them
in
the DQ-10s. They worked fine. I kept the volume down at first, but the
drivers continued to work. After several hours I gathered my courage and
turned things up to a perfectly satisfying listening level (loud, but not
super loud). The drivers kept working, and are still working two days
later.
I've replaced the 3-amp speaker fuses with 2-amp units, and I don't intend
ever crank the system up really loud. But I'm very happy to have my
DQ-10s back.

Incidentally, I don't notice any difference in sound now that the midbass
units are functioning. This may be partly due to the narrow 400-1000 Hz
range the drivers operate in and the first-order crossover that allows the
adjacent-frequency drivers to emit a fair amount of power in this
passband.
But I think it's mostly due to my lack of listening acuity.

I don't know whether this driver revival will last. It's hard to believe
that a spark can make a reliable weld. But perhaps the break was not in
the
voice coil itself. Maybe the solder joining the stranded leads to the
voice
coil wire had melted, and the spark simply did a remelt. This might have a
better long-term chance of survival. These junctions are not visible on
the
midbass unit as they are on the surface of the woofer cone.

Even if this fix doesn't last, at least it revived the drivers long enough
that I could make some measurements. If I ever do need to get some
replacements, I'll have a better idea what to look for.

Brian

"jriegle" wrote in news:ZCZhb.176674$3o3.13119996
@bgtnsc05-news.ops.worldnet.att.net:

Interesting. Zapping something like that should widen the gap kinda the
way
a fuse works.
John

John,

One would think, but there are many ways that a connection can go bad. He
might have had a bad solder joint internally that when the cap discharged,
caused the joint to weld itself into working again. If that is the case,
the 'quick' fix will likely last a long time.

r



"Brian" wrote in message
om...
A couple days ago I was near one of my Dahlquist DQ-10s when I heard
something funny. It sounded like a low-level intermittent connection.
It
had
that unmistakable local character--definitely not program material--and
seemed to be coming from the midrange driver (I later learned that this
unit
is called the midbass in this five-driver system). I rotated the treble
control on the rear of the speaker cabinet, thinking a dirty pot might
be
responsible (even though this alters the level of another driver). By
that point the intermittent sound had stopped. It seemed that nothing
at
all
was coming from the driver. I removed the rear screen, and with an
ohmmeter
determined that the voice coil was open.

I unmounted the driver and examined it. It looked perfect. I bounced it
around a bit and once briefly managed to read about 60 ohms across the
voice
coil, but basically it was dead. I remembered that years earlier I had
once
popped the 3-amp fuse in that speaker. I couldn't recall the
circumstances,
but I figured the voice coil probably had blown at that time.

The strange thing is that I hadn't noticed anything amiss with the
sound,
and I remembered that the mono sound image was always properly
centered. I
checked the other speaker, and sure enough, its midbass was open too. I
played some familiar music and everything sounded normal. So much for
my
ears!

Although I hadn't sat down and listened seriously to my system in a
long
time, since buying my DQ-10s new in the early 1980s I had always loved
them.
I was pretty sad about having blown them up. After checking on the
Internet,
I learned that this particular driver had not been manufactured in a
long
time and was now unavailable. Bummer. One place said they could rebuild
them. I sent an e-mail asking how much it would cost, but after seeing
what
they charged for other drivers, I knew I wouldn't be willing to spend
the
hundreds they were likely to ask to repair a pair. Other sites offered
replacement drivers, but I was very skeptical that the properties would
be
similar enough to the original drivers. If only I had just one working
driver to measure a few parameters. Then I might be able to select a
reasonable replacement. I didn't even know the impedance.

The next morning I considered opening up the drivers and attempting to
fix
the voice coil myself. I had never done anything like that, but I
figured
the drivers were useless the way they were, so why not give it a try.
Then
I
started thinking about the probable failure mechanism. I assumed that I
had
overheated the voice coil wire and melted it in one spot. Since the
current
stops as soon as a break occurs, I figured the gap between the broken
segments was likely to be quite small.

I wondered whether I might apply a high voltage, bridge the gap with an
arc,
and remelt the wire ends together. It was worth a shot. I charged a 47
uF
capacitor to 100 volts and touched it to the driver terminals. There
was a
loud whomp that scared the **** out of me. Then I realized that it was
just
the cone responding to the current impulse, which meant I had
continuity.
The voice coil measured 6.8 ohms! I connected the driver to a little
push-pull 6V6 amp I had nearby. What a relief--it sounded perfectly
normal!
I turned the volume up to clipping (12 watts) for a short while and the
driver continued to work. At least it was able to handle more than flea
power, though for how long I didn't know.

I zapped the other blown driver. Whomp! and 7.1 ohms. It too sounded
fine.

I made a few simple measurements on the drivers and then reinstalled
them
in
the DQ-10s. They worked fine. I kept the volume down at first, but the
drivers continued to work. After several hours I gathered my courage
and
turned things up to a perfectly satisfying listening level (loud, but
not
super loud). The drivers kept working, and are still working two days
later.
I've replaced the 3-amp speaker fuses with 2-amp units, and I don't
intend
ever crank the system up really loud. But I'm very happy to have my
DQ-10s back.

Incidentally, I don't notice any difference in sound now that the
midbass
units are functioning. This may be partly due to the narrow 400-1000 Hz
range the drivers operate in and the first-order crossover that allows
the
adjacent-frequency drivers to emit a fair amount of power in this
passband.
But I think it's mostly due to my lack of listening acuity.

I don't know whether this driver revival will last. It's hard to
believe
that a spark can make a reliable weld. But perhaps the break was not in
the
voice coil itself. Maybe the solder joining the stranded leads to the
voice
coil wire had melted, and the spark simply did a remelt. This might
have a
better long-term chance of survival. These junctions are not visible on
the
midbass unit as they are on the surface of the woofer cone.

Even if this fix doesn't last, at least it revived the drivers long
enough
that I could make some measurements. If I ever do need to get some
replacements, I'll have a better idea what to look for.

Brian






--
Nothing beats the bandwidth of a station wagon filled with DLT tapes.

In article
,
"jriegle" wrote:

Interesting. Zapping something like that should widen the gap kinda the way
a fuse works.
John


I've seen the zap trick work too. It's oxide on a loose rivet on the
cone where the coil wire and tinsel wire meet. A power surge blows away
the crud and welds the wire for a little while. It eventually cracks
and corrodes again. There's no practical way to fix the rivet unless
you can get the cap off the cone with a heat gun. If you can get the
cap off, the spark should be easy to see in the dark.

In , on 10/10/03
at 04:40 AM, (Brian) said:
[ ... ]

I charged a 47 uF
capacitor to 100 volts and touched it to the driver terminals. There
was a loud whomp that scared the **** out of me. Then I realized that
it was just the cone responding to the current impulse, which meant I
had continuity. The voice coil measured 6.8 ohms! I connected the
driver to a little push-pull 6V6 amp I had nearby. What a relief--it
sounded perfectly normal! I turned the volume up to clipping (12
watts) for a short while and the driver continued to work. At least it
was able to handle more than flea power, though for how long I didn't
know.

[ ... ]

One never knows how long such a "repair" will last, but it's often
productive to try it at home. You'll get differing opinions from
professional servicers because customers expect some sort of warranty
on the repair. Since one never knows exactly where the break was or how
strong the repair might be, the pro's can't offer this as an option.

Sometimes I'll suggest this approach, but I always stress that any
success is more luck than skill.

-----------------------------------------------------------
SPAM:
wordgame:123(abc):14 9 20 5 2 9 18 4 at 22 15 9 3 5 14 5 20 dot 3 15
13 (Barry Mann)
[sorry about the puzzle, SPAMers are ruining my mailbox]
-----------------------------------------------------------

In , on 10/10/03
at 04:40 AM, (Brian) said:
[ ... ]

I charged a 47 uF
capacitor to 100 volts and touched it to the driver terminals. There
was a loud whomp that scared the **** out of me. Then I realized that
it was just the cone responding to the current impulse, which meant I
had continuity. The voice coil measured 6.8 ohms! I connected the
driver to a little push-pull 6V6 amp I had nearby. What a relief--it
sounded perfectly normal! I turned the volume up to clipping (12
watts) for a short while and the driver continued to work. At least it
was able to handle more than flea power, though for how long I didn't
know.

[ ... ]

One never knows how long such a "repair" will last, but it's often
productive to try it at home. You'll get differing opinions from
professional servicers because customers expect some sort of warranty
on the repair. Since one never knows exactly where the break was or how
strong the repair might be, the pro's can't offer this as an option.

Sometimes I'll suggest this approach, but I always stress that any
success is more luck than skill.

-----------------------------------------------------------
SPAM:
wordgame:123(abc):14 9 20 5 2 9 18 4 at 22 15 9 3 5 14 5 20 dot 3 15
13 (Barry Mann)
[sorry about the puzzle, SPAMers are ruining my mailbox]
-----------------------------------------------------------

Sometimes I'll suggest this approach, but I always stress that any
success is more luck than skill.


Barry, I'd be interested to know your experience with this trick. It
sounds like you may have had a mixture of long-term success and
failure. My Dahlquist midbass drivers are still working, but I don't
dare push them, and I'm skeptical the fix will last.

I'm now two out of three. Last weekend I bought a cheap
concentric-horn PA speaker at a garage sale. When I got home I found
that the voice coil was open. I tried the capacitor trick. The speaker
ponged when I applied the charge, but the voice coil remained open. I
took the speaker apart to see what was up. The voice coil wire had
broken just beyond the coil itself, where it curved to run across to
the terminal. An odd place to break if the original problem was heat
dissipation, as I'd expect the center of the coil to be the hottest
spot. Anyway, I soldered the wire back together and the speaker
worked. (But once I heard the audio quality, I tossed it into the
scrap pile.)

Brian

Sometimes I'll suggest this approach, but I always stress that any
success is more luck than skill.


Barry, I'd be interested to know your experience with this trick. It
sounds like you may have had a mixture of long-term success and
failure. My Dahlquist midbass drivers are still working, but I don't
dare push them, and I'm skeptical the fix will last.

I'm now two out of three. Last weekend I bought a cheap
concentric-horn PA speaker at a garage sale. When I got home I found
that the voice coil was open. I tried the capacitor trick. The speaker
ponged when I applied the charge, but the voice coil remained open. I
took the speaker apart to see what was up. The voice coil wire had
broken just beyond the coil itself, where it curved to run across to
the terminal. An odd place to break if the original problem was heat
dissipation, as I'd expect the center of the coil to be the hottest
spot. Anyway, I soldered the wire back together and the speaker
worked. (But once I heard the audio quality, I tossed it into the
scrap pile.)

Brian

In , on 10/19/03
at 07:59 AM, (Brian) said:

Sometimes I'll suggest this approach, but I always stress that any
success is more luck than skill.


Barry, I'd be interested to know your experience with this trick. It
sounds like you may have had a mixture of long-term success and
failure. My Dahlquist midbass drivers are still working, but I don't
dare push them, and I'm skeptical the fix will last.

Most of the time this is a fragile repair. The next flex or temperature
cycle will break the weld. If you could know the wire size, gap, and
thermal characteristics of the substrate you could calculate the exact
charge to make a good weld. More likely than not, any type of voice
coil repair will fail.

I'm now two out of three. Last weekend I bought a cheap
concentric-horn PA speaker at a garage sale. When I got home I found
that the voice coil was open. I tried the capacitor trick. The speaker
ponged when I applied the charge, but the voice coil remained open. I
took the speaker apart to see what was up. The voice coil wire had
broken just beyond the coil itself, where it curved to run across to
the terminal. An odd place to break if the original problem was heat
dissipation, as I'd expect the center of the coil to be the hottest
spot. Anyway, I soldered the wire back together and the speaker
worked. (But once I heard the audio quality, I tossed it into the
scrap pile.)

In this case I suspect that there was a weak spot in the wire, probably
caused at the time of manufacture. The wire could have been kinked or
nicked and after a few billion flexes, failed.

Soldering a voice coil break usually is a short term fix because solder
is not flexible and I find that you usually create a hard spot in the
wire at the edge of the solder ball. Eventually, the wire will fail at
the junction between the wire and solder. Assuming you can properly
prepare the wire, the solder joint rarely fails. In close tolerance
situations you may not be able to make a repair that slips back into
the magnet gap.

If the coil was overheated, one can usually see some discoloration or
blistering of the insulation.

Sometimes I get lucky and there is a bad connection where the flex
leads connect to the terminals. This is a fairly easy repair, but
proper surface preparation is crucial (that's usually why it failed.)

-----------------------------------------------------------
SPAM:
wordgame:123(abc):14 9 20 5 2 9 18 4 at 22 15 9 3 5 14 5 20 dot 3 15
13 (Barry Mann)
[sorry about the puzzle, SPAMers are ruining my mailbox]
-----------------------------------------------------------

In , on 10/19/03
at 07:59 AM, (Brian) said:

Sometimes I'll suggest this approach, but I always stress that any
success is more luck than skill.


Barry, I'd be interested to know your experience with this trick. It
sounds like you may have had a mixture of long-term success and
failure. My Dahlquist midbass drivers are still working, but I don't
dare push them, and I'm skeptical the fix will last.

Most of the time this is a fragile repair. The next flex or temperature
cycle will break the weld. If you could know the wire size, gap, and
thermal characteristics of the substrate you could calculate the exact
charge to make a good weld. More likely than not, any type of voice
coil repair will fail.

I'm now two out of three. Last weekend I bought a cheap
concentric-horn PA speaker at a garage sale. When I got home I found
that the voice coil was open. I tried the capacitor trick. The speaker
ponged when I applied the charge, but the voice coil remained open. I
took the speaker apart to see what was up. The voice coil wire had
broken just beyond the coil itself, where it curved to run across to
the terminal. An odd place to break if the original problem was heat
dissipation, as I'd expect the center of the coil to be the hottest
spot. Anyway, I soldered the wire back together and the speaker
worked. (But once I heard the audio quality, I tossed it into the
scrap pile.)

In this case I suspect that there was a weak spot in the wire, probably
caused at the time of manufacture. The wire could have been kinked or
nicked and after a few billion flexes, failed.

Soldering a voice coil break usually is a short term fix because solder
is not flexible and I find that you usually create a hard spot in the
wire at the edge of the solder ball. Eventually, the wire will fail at
the junction between the wire and solder. Assuming you can properly
prepare the wire, the solder joint rarely fails. In close tolerance
situations you may not be able to make a repair that slips back into
the magnet gap.

If the coil was overheated, one can usually see some discoloration or
blistering of the insulation.

Sometimes I get lucky and there is a bad connection where the flex
leads connect to the terminals. This is a fairly easy repair, but
proper surface preparation is crucial (that's usually why it failed.)

-----------------------------------------------------------
SPAM:
wordgame:123(abc):14 9 20 5 2 9 18 4 at 22 15 9 3 5 14 5 20 dot 3 15
13 (Barry Mann)
[sorry about the puzzle, SPAMers are ruining my mailbox]
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the junction between the wire and solder. Assuming you can properly
prepare the wire, the solder joint rarely fails. In close tolerance


What sort of preparation is necessary (also for the flex leads mentioned later)?

Brian

the junction between the wire and solder. Assuming you can properly
prepare the wire, the solder joint rarely fails. In close tolerance


What sort of preparation is necessary (also for the flex leads mentioned later)?

Brian

In , on 10/20/03
at 07:16 AM, (Brian) said:

the junction between the wire and solder. Assuming you can properly
prepare the wire, the solder joint rarely fails. In close tolerance


What sort of preparation is necessary (also for the flex leads
mentioned later)?

Same as for any soldering process, the surfaces must be dirt, grease,
insulation, and oxide free. Some manufacturers use aluminum wires.
Aluminum requires special flux. If the joint failed, it wasn't done
right by the manufacturer and probably has hard to remove crud you'll
have to deal with.

Voice coils use magnet wire. Magnet wire is always insulated, and the
insulation must be tough in order to withstand the coil winding
process. Sometimes the insulation is nearly transparent and
inexperienced solderers might not know it is present. Scraping the wire
to remove the insulation can easily damage the wire, thus setting up
the next failure. Chemical removal of the insulation is safest for the
wire, but the chemicals are very harsh.

-----------------------------------------------------------
SPAM:
wordgame:123(abc):14 9 20 5 2 9 18 4 at 22 15 9 3 5 14 5 20 dot 3 15
13 (Barry Mann)
[sorry about the puzzle, SPAMers are ruining my mailbox]
-----------------------------------------------------------

In , on 10/20/03
at 07:16 AM, (Brian) said:

the junction between the wire and solder. Assuming you can properly
prepare the wire, the solder joint rarely fails. In close tolerance


What sort of preparation is necessary (also for the flex leads
mentioned later)?

Same as for any soldering process, the surfaces must be dirt, grease,
insulation, and oxide free. Some manufacturers use aluminum wires.
Aluminum requires special flux. If the joint failed, it wasn't done
right by the manufacturer and probably has hard to remove crud you'll
have to deal with.

Voice coils use magnet wire. Magnet wire is always insulated, and the
insulation must be tough in order to withstand the coil winding
process. Sometimes the insulation is nearly transparent and
inexperienced solderers might not know it is present. Scraping the wire
to remove the insulation can easily damage the wire, thus setting up
the next failure. Chemical removal of the insulation is safest for the
wire, but the chemicals are very harsh.

-----------------------------------------------------------
SPAM:
wordgame:123(abc):14 9 20 5 2 9 18 4 at 22 15 9 3 5 14 5 20 dot 3 15
13 (Barry Mann)
[sorry about the puzzle, SPAMers are ruining my mailbox]
-----------------------------------------------------------

(Brian) wrote in message . com...
the junction between the wire and solder. Assuming you can properly
prepare the wire, the solder joint rarely fails. In close tolerance


What sort of preparation is necessary (also for the flex leads
mentioned later)?

Really nothing beyond what is required for any good solder joint under
any other circumstances:

1. The adjoining parts be chemically clean

2. The adjoining parts already be mechanically secure
BEFORE the joint is soldered

3. That sufficient adjoing area be made available for the
joint.

4. The appropriate flux is applied to ensure proper chemical
state while soldering.

5. The appropriate solder is used for the application

6. Sufficient heat is applied to ensure the solder reaches
its liquid state quickly, but not to much so that heat
damage results to sensitive parts, that heat is not
dissippated unduly by the parts or other surrounding
structures, and that the joint is left undisturbed while
it cools, hopefully evenly to below the liquification
temperature.

All this is EASY to to in applications OTHER than what you are
trying to do. The most important flaw, in your situation, seems
to be the inability to ensure points 1, 2, 3 and 6. In other
words, not meeting 4 out of 6 requirements almost guarantees
a failed job.

(Brian) wrote in message . com...
the junction between the wire and solder. Assuming you can properly
prepare the wire, the solder joint rarely fails. In close tolerance


What sort of preparation is necessary (also for the flex leads
mentioned later)?

Really nothing beyond what is required for any good solder joint under
any other circumstances:

1. The adjoining parts be chemically clean

2. The adjoining parts already be mechanically secure
BEFORE the joint is soldered

3. That sufficient adjoing area be made available for the
joint.

4. The appropriate flux is applied to ensure proper chemical
state while soldering.

5. The appropriate solder is used for the application

6. Sufficient heat is applied to ensure the solder reaches
its liquid state quickly, but not to much so that heat
damage results to sensitive parts, that heat is not
dissippated unduly by the parts or other surrounding
structures, and that the joint is left undisturbed while
it cools, hopefully evenly to below the liquification
temperature.

All this is EASY to to in applications OTHER than what you are
trying to do. The most important flaw, in your situation, seems
to be the inability to ensure points 1, 2, 3 and 6. In other
words, not meeting 4 out of 6 requirements almost guarantees
a failed job.