Cherokee Strobe Noise

[Jonathan Goodish]

I know that this has been beaten to death, and I have searched the
archives, but I'm trying to narrow my specific case down a little bit.

I have a Cherokee with factory-installed wing tip strobes. I have an
original (1977) King Silver Crown avionics package, including audio
panel, KX170Bs, etc. I also have a Sigtronics panel-mount 4 place
intercom that was installed at some point before I purchased the
plane... I believe it is a SPA-400.

Everything is fine, except that the wing tip strobes can be heard like a
siren in the headsets. The siren sound is also occasionally transmitted
over the radio when we make transmissions, because I have been told to
"check my ELT" after making transmissions. Here are my observations:

1 -- Noise is present with intercom on or off.

2 -- Noise is WORSE when any radio, but especially marker beacon, is
selected on the audio panel.

3 -- When all radios are unselected on the audio panel (i.e. nothing
selected to either speaker or headsets) noise goes from very noticeable
to barely noticeable.

4 -- Noise is much WORSE when things are "cold." After about 20 minutes
of flying time, the noise is still noticeable, but not nearly as bad as
it was when the flight began.

5 -- Unless I'm hearing things, which is possible, I can SOMETIMES hear
the noise through the headset with the strobes on but avionics bus OFF.

I am not sure whether the strobe power pack is crying out for help,
whether I have a ground problem elsewhere in the system, or whether I
have an improper installation of something (like the intercom), or
whether the audio panel is shot.

The strobes were factory-installed, so I assume that the installation of
the strobes is correct. The SPA-400 intercom was obviously not factory
installed, and I am not convinced that insulating washers were used on
the headset plugs, so I do need to check that out. I do know that
shielded cable was NOT used on the intercom installation.

Does anyone have any ideas? I've basically narrowed it down to three
things, in no particular order:

1 -- intercom
2 -- audio panel
3 -- strobe power pack


Thanks,
JKG

[John_F]

On Wed, 27 Oct 2004 00:43:50 GMT, Jonathan Goodish
> wrote:

>I know that this has been beaten to death, and I have searched the
>archives, but I'm trying to narrow my specific case down a little bit.
>
>I have a Cherokee with factory-installed wing tip strobes. I have an
>original (1977) King Silver Crown avionics package, including audio
>panel, KX170Bs, etc. I also have a Sigtronics panel-mount 4 place
>intercom that was installed at some point before I purchased the
>plane... I believe it is a SPA-400.
>
>Everything is fine, except that the wing tip strobes can be heard like a
>siren in the headsets. The siren sound is also occasionally transmitted
>over the radio when we make transmissions, because I have been told to
>"check my ELT" after making transmissions. Here are my observations:
>
>1 -- Noise is present with intercom on or off.

Conclusion, it is not coming in within the intercom.
>
>2 -- Noise is WORSE when any radio, but especially marker beacon, is
>selected on the audio panel.

The noise is coupling into the marker beacon audio. Is the marker
beacon ground connection the same point as the strobe ground? Is the
marker beacon audio lead shielded wire?
>
>3 -- When all radios are unselected on the audio panel (i.e. nothing
>selected to either speaker or headsets) noise goes from very noticeable
>to barely noticeable.

Sounds like a nosy ground problem.
>
>4 -- Noise is much WORSE when things are "cold." After about 20 minutes
>of flying time, the noise is still noticeable, but not nearly as bad as
>it was when the flight began.

Sounds even more like a loose ground problem. Aluminum srinks more
with cold temperatures than the steel screw that holds the wire to the
airframe.
>
>5 -- Unless I'm hearing things, which is possible, I can SOMETIMES hear
>the noise through the headset with the strobes on but avionics bus OFF.

If the ground resistance were bad enough it would do this.
>
>I am not sure whether the strobe power pack is crying out for help,
>whether I have a ground problem elsewhere in the system, or whether I
>have an improper installation of something (like the intercom), or
>whether the audio panel is shot.

Find out where the ground of the strobe pack is connected to the
airframe and clean it.
>
>The strobes were factory-installed, so I assume that the installation of
>the strobes is correct.

Don't bet on this.

>The SPA-400 intercom was obviously not factory
>installed, and I am not convinced that insulating washers were used on
>the headset plugs, so I do need to check that out.

Unless you have a large current through the airframe or have some poor
ground points insulating the jacks may be a wasted effort. If it does
work you need to look at the ground connections for the radios ,
intercom and audio panel because they will almost certainly be not
tight and will be high resistance.

>I do know that shielded cable was NOT used on the intercom installation.

VERY VERY BAD!!! This is how the noise is coupling from the strobe
power leads on to the audio leads if they are in the same wire bundle.
ALL of the audio leads MUST be shielded wire.
>
>Does anyone have any ideas? I've basically narrowed it down to three
>things, in no particular order:
>
>1 -- intercom
>2 -- audio panel
>3 -- strobe power pack
>
A big 1000uf cowpasture on the strobe power pack input power may help.
>
>Thanks,
>JKG

Find a avionics shop that knows what they are doing and have them fix
it. They are very hard to find and generally will NOT have the lowest
rates but they will generally save you money.

John

[Jonathan Goodish]

In article >,
(John_F) wrote:
> >2 -- Noise is WORSE when any radio, but especially marker beacon, is
> >selected on the audio panel.
>
> The noise is coupling into the marker beacon audio. Is the marker
> beacon ground connection the same point as the strobe ground? Is the
> marker beacon audio lead shielded wire?

I don't know the answer to either question off-hand, but I do know that
the marker beacon receiver is on the shelf in the tail that is not too
far from the strobe power pack.



> VERY VERY BAD!!! This is how the noise is coupling from the strobe
> power leads on to the audio leads if they are in the same wire bundle.
> ALL of the audio leads MUST be shielded wire.

Yes, I know that this is bad, but it probably could be worse (and
remember, I'm not responsible for the intercom installation). The leads
to and from the intercom don't appear to be bundled with the strobe
power leads, or even close to them. I am hoping that this isn't the big
problem, and I can let this ride until I have the interior replaced and
then replace the wiring at that point.



> Find a avionics shop that knows what they are doing and have them fix
> it. They are very hard to find and generally will NOT have the lowest
> rates but they will generally save you money.

I don't want to give someone a blank check to troubleshoot a problem
without some idea of what it may be. In other words, I need to try to
troubleshoot as much as possible before engaging the avionics shop for
more in-depth troubleshooting. I do believe that I have a good avionics
shop in the local area, and they've done work for me before, but I
haven't classified this problem as more than a nuisance at this point.
However, it may be getting worse, and I certainly don't want it to reach
a point where it becomes a show-stopper.


JKG

[Ron Rosenfeld]

On Wed, 27 Oct 2004 00:43:50 GMT, Jonathan Goodish >
wrote:

>Everything is fine, except that the wing tip strobes can be heard like a
>siren in the headsets.

Sounds like a problem I have had with a Whelen power pack.

Can you hear the sound at the power pack? I could.

When I called Whelen, I was told that the problem was a bad capacitor.
They told me which capacitor to replace. I replaced it and it worked fine
for a few years, although the noise is just now starting to come back.

The power pack, however, is riveted closed. So I had to drill out the
rivets, replace the electrolytic capacitor, and put the box back together.
Took about 10 minutes on the phone with Whelen tech support; 30 minutes of
labor and a $2.30 capacitor. Needed some pop rivets, too, to put the box
back together.



Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

[Michelle P]

Jonathan,
Do you have a capacitor across your alternator output? If so that may be
bad as well. The last one about the capacitor in the unit sound likely
as well. The repair though sounds a little well not completely legal
unless they are an A&P and have the manual that says they can replace
the part.
Michelle

Jonathan Goodish wrote:

>I know that this has been beaten to death, and I have searched the
>archives, but I'm trying to narrow my specific case down a little bit.
>
>I have a Cherokee with factory-installed wing tip strobes. I have an
>original (1977) King Silver Crown avionics package, including audio
>panel, KX170Bs, etc. I also have a Sigtronics panel-mount 4 place
>intercom that was installed at some point before I purchased the
>plane... I believe it is a SPA-400.
>
>Everything is fine, except that the wing tip strobes can be heard like a
>siren in the headsets. The siren sound is also occasionally transmitted
>over the radio when we make transmissions, because I have been told to
>"check my ELT" after making transmissions. Here are my observations:
>
>1 -- Noise is present with intercom on or off.
>
>2 -- Noise is WORSE when any radio, but especially marker beacon, is
>selected on the audio panel.
>
>3 -- When all radios are unselected on the audio panel (i.e. nothing
>selected to either speaker or headsets) noise goes from very noticeable
>to barely noticeable.
>
>4 -- Noise is much WORSE when things are "cold." After about 20 minutes
>of flying time, the noise is still noticeable, but not nearly as bad as
>it was when the flight began.
>
>5 -- Unless I'm hearing things, which is possible, I can SOMETIMES hear
>the noise through the headset with the strobes on but avionics bus OFF.
>
>I am not sure whether the strobe power pack is crying out for help,
>whether I have a ground problem elsewhere in the system, or whether I
>have an improper installation of something (like the intercom), or
>whether the audio panel is shot.
>
>The strobes were factory-installed, so I assume that the installation of
>the strobes is correct. The SPA-400 intercom was obviously not factory
>installed, and I am not convinced that insulating washers were used on
>the headset plugs, so I do need to check that out. I do know that
>shielded cable was NOT used on the intercom installation.
>
>Does anyone have any ideas? I've basically narrowed it down to three
>things, in no particular order:
>
>1 -- intercom
>2 -- audio panel
>3 -- strobe power pack
>
>
>Thanks,
>JKG
>
>

--

Michelle P ATP-ASEL, CP-AMEL, and AMT-A&P

"Elisabeth" a Maule M-7-235B (no two are alike)

Volunteer Pilot, Angel Flight Mid-Atlantic

Volunteer Builder, Habitat for Humanity

[Ron Rosenfeld]

On Wed, 27 Oct 2004 11:45:50 GMT, Michelle P
> wrote:

>Jonathan,
>Do you have a capacitor across your alternator output? If so that may be
>bad as well. The last one about the capacitor in the unit sound likely
>as well. The repair though sounds a little well not completely legal
>unless they are an A&P and have the manual that says they can replace
>the part.
>Michelle

The repair was performed under the supervision of an IA.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

[Al Marzo]

And did John mention that he feels it's a GROUND problem? Also, how
could you have the strobes installed at the factory without shielded
wire? Were they added at some point? If you're able, check all
grounds before spending money with a shop.

On Wed, 27 Oct 2004 02:20:37 GMT, (John_F) wrote:

>On Wed, 27 Oct 2004 00:43:50 GMT, Jonathan Goodish
> wrote:
>
>>I know that this has been beaten to death, and I have searched the
>>archives, but I'm trying to narrow my specific case down a little bit.
>>
>>I have a Cherokee with factory-installed wing tip strobes. I have an
>>original (1977) King Silver Crown avionics package, including audio
>>panel, KX170Bs, etc. I also have a Sigtronics panel-mount 4 place
>>intercom that was installed at some point before I purchased the
>>plane... I believe it is a SPA-400.
>>
>>Everything is fine, except that the wing tip strobes can be heard like a
>>siren in the headsets. The siren sound is also occasionally transmitted
>>over the radio when we make transmissions, because I have been told to
>>"check my ELT" after making transmissions. Here are my observations:
>>
>>1 -- Noise is present with intercom on or off.
>
>Conclusion, it is not coming in within the intercom.
>>
>>2 -- Noise is WORSE when any radio, but especially marker beacon, is
>>selected on the audio panel.
>
>The noise is coupling into the marker beacon audio. Is the marker
>beacon ground connection the same point as the strobe ground? Is the
>marker beacon audio lead shielded wire?
>>
>>3 -- When all radios are unselected on the audio panel (i.e. nothing
>>selected to either speaker or headsets) noise goes from very noticeable
>>to barely noticeable.
>
> Sounds like a nosy ground problem.
>>
>>4 -- Noise is much WORSE when things are "cold." After about 20 minutes
>>of flying time, the noise is still noticeable, but not nearly as bad as
>>it was when the flight began.
>
>Sounds even more like a loose ground problem. Aluminum srinks more
>with cold temperatures than the steel screw that holds the wire to the
>airframe.
>>
>>5 -- Unless I'm hearing things, which is possible, I can SOMETIMES hear
>>the noise through the headset with the strobes on but avionics bus OFF.
>
>If the ground resistance were bad enough it would do this.
>>
>>I am not sure whether the strobe power pack is crying out for help,
>>whether I have a ground problem elsewhere in the system, or whether I
>>have an improper installation of something (like the intercom), or
>>whether the audio panel is shot.
>
>Find out where the ground of the strobe pack is connected to the
>airframe and clean it.
>>
>>The strobes were factory-installed, so I assume that the installation of
>>the strobes is correct.
>
>Don't bet on this.
>
>>The SPA-400 intercom was obviously not factory
>>installed, and I am not convinced that insulating washers were used on
>>the headset plugs, so I do need to check that out.
>
>Unless you have a large current through the airframe or have some poor
>ground points insulating the jacks may be a wasted effort. If it does
>work you need to look at the ground connections for the radios ,
>intercom and audio panel because they will almost certainly be not
>tight and will be high resistance.
>
>>I do know that shielded cable was NOT used on the intercom installation.
>
>VERY VERY BAD!!! This is how the noise is coupling from the strobe
>power leads on to the audio leads if they are in the same wire bundle.
>ALL of the audio leads MUST be shielded wire.
>>
>>Does anyone have any ideas? I've basically narrowed it down to three
>>things, in no particular order:
>>
>>1 -- intercom
>>2 -- audio panel
>>3 -- strobe power pack
>>
>A big 1000uf cowpasture on the strobe power pack input power may help.
>>
>>Thanks,
>>JKG
>
>Find a avionics shop that knows what they are doing and have them fix
>it. They are very hard to find and generally will NOT have the lowest
>rates but they will generally save you money.
>
>John

[[email protected]]

Jonathan Goodish > wrote:
: > VERY VERY BAD!!! This is how the noise is coupling from the strobe
: > power leads on to the audio leads if they are in the same wire bundle.
: > ALL of the audio leads MUST be shielded wire.

: Yes, I know that this is bad, but it probably could be worse (and
: remember, I'm not responsible for the intercom installation). The leads
: to and from the intercom don't appear to be bundled with the strobe
: power leads, or even close to them. I am hoping that this isn't the big
: problem, and I can let this ride until I have the interior replaced and
: then replace the wiring at that point.
Not that big of a deal, actually. Shielding gets an over-used emphasis in
most installations. There is not that much coupling between adjacent wires at audio
frequencies (<4kHz). Not that there isn't any, but for any signal it's small. For
any signal above mic level, it's fairly insignificant. Also, only the inductive
coupling has any important coupling for a wiring bundle with the types of impedances
used in a typicaly aircraft system, so only wires carrying current can couple noise.

: > Find a avionics shop that knows what they are doing and have them fix
: > it. They are very hard to find and generally will NOT have the lowest
: > rates but they will generally save you money.

: I don't want to give someone a blank check to troubleshoot a problem
: without some idea of what it may be. In other words, I need to try to
: troubleshoot as much as possible before engaging the avionics shop for
: more in-depth troubleshooting. I do believe that I have a good avionics
: shop in the local area, and they've done work for me before, but I
: haven't classified this problem as more than a nuisance at this point.
: However, it may be getting worse, and I certainly don't want it to reach
: a point where it becomes a show-stopper.

Good idea. It will depend on how friendly your A&P is with you crawling under
the panel, removing things to get at wiring, and tracing the wiring itself. It's
probably about 95% certain that it's a ground loop issue... in particular with the MB
it sounds like. Since many installers will ground different avionics willy-nilly
throughout the airframe wherever it's convenient, you get ground currents causing
voltage drops everywhere and coupling into the audio system.

Since you said things change as they heat up, it might help a bit to try to
locate the grounds on all the audio equipment and clean them. Most likely, however,
it's due to things being grounded at different places.

You might be able to band-aid the specific problem of strobe noise by running
a dedicated ground wire to it from "some good ground." That "some good ground" sorta
depends, but good places to try for troubleshooting would be the battery negative, and
alternator casing. That doesn't fix the multipoint ground problem in the audio
system, but it might reduce the structural ground currents enough to reduce the noise.

Cheers,
-cory


--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

[[email protected]]

I'd vote for adding filter capacitor(s) at the strobe power supply 12V
(or whatever) input, immediately adjacent to the power supply.
Something sound fishy inside that strobe power supply.

Where's Jim Weir when you need him?

[Jonathan Goodish]

In article >,
Ron Rosenfeld > wrote:
> >Everything is fine, except that the wing tip strobes can be heard like a
> >siren in the headsets.
>
> Sounds like a problem I have had with a Whelen power pack.
>
> Can you hear the sound at the power pack? I could.

Yes, I can. I can hear it when I'm standing outside the airplane with
the strobes on -- it's that loud. Seems to quiet down a little when it
warms up.

I figured that, one way or the other, the big fix was going to be
pulling the power pack, but I wanted to make sure there wasn't something
else that I was overlooking.


JKG

[PaulaJay1]

In article >, Jonathan
Goodish > writes:

>I have a Cherokee with factory-installed wing tip strobes. I have an
>original (1977) King Silver Crown avionics package, including audio
>panel, KX170Bs, etc. I also have a Sigtronics panel-mount 4 place
>intercom that was installed at some point before I purchased the
>plane... I believe it is a SPA-400.
>
>Everything is fine, except that the wing tip strobes can be heard like a
>siren in the headsets. The siren sound is also occasionally transmitted
>over the radio when we make transmissions, because I have been told to
>"check my ELT" after making transmissions. Here are my observations:

I had this problem and I fixed it by adding a capacitor across the 12 volt
input at the high voltage power supply and placed a choke ahead of the input
(nearer the battery). My power supply is in the tail and the cap/choke killed
the high freq at the source.
Chuck

[Mike Spera]

Whelen told you all that. Strange, they mark the case as "Not Field
Repairable" and then they let their techs violate their own rule. The
FAA police would surely frown. Their lawyers would squirm quite a bit
also. If you ever crash, have your family sue Whelen for $50 million
because the plane obviously crashed because of their "negligence" in
giving you "defective" repair information. My cut for this advice is
only 30%...

Mike

Ron Rosenfeld wrote:

> On Wed, 27 Oct 2004 00:43:50 GMT, Jonathan Goodish >
> wrote:
>
>
>>Everything is fine, except that the wing tip strobes can be heard like a
>>siren in the headsets.
>
>
> Sounds like a problem I have had with a Whelen power pack.
>
> Can you hear the sound at the power pack? I could.
>
> When I called Whelen, I was told that the problem was a bad capacitor.
> They told me which capacitor to replace. I replaced it and it worked fine
> for a few years, although the noise is just now starting to come back.
>
> The power pack, however, is riveted closed. So I had to drill out the
> rivets, replace the electrolytic capacitor, and put the box back together.
> Took about 10 minutes on the phone with Whelen tech support; 30 minutes of
> labor and a $2.30 capacitor. Needed some pop rivets, too, to put the box
> back together.
>
>
>
> Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

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[David Lesher]

Jonathan Goodish > writes:


>Everything is fine, except that the wing tip strobes can be heard like a
>siren in the headsets. The siren sound is also occasionally transmitted
>over the radio when we make transmissions, because I have been told to
>"check my ELT" after making transmissions. Here are my observations:


Has it always been that that way; or has it be getting worse?

In either case, I'll add another. Clean and check the battery
connections and any/all engine/alternator ground straps. BOTH ENDS.
You typically have a ground lug that's connecting to a dissimilar
metal; that's corrosion city.

Why does it matter? Well, the battery is [also] a whopping big
capacitor; you want low impedence connections to it.

--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

[Ron Rosenfeld]

On 28 Oct 2004 02:40:04 GMT, Mike Spera > wrote:

>Whelen told you all that. Strange, they mark the case as "Not Field
>Repairable" and then they let their techs violate their own rule. The
>FAA police would surely frown. Their lawyers would squirm quite a bit
>also. If you ever crash, have your family sue Whelen for $50 million
>because the plane obviously crashed because of their "negligence" in
>giving you "defective" repair information. My cut for this advice is
>only 30%...

I will accord your advice a value equal to less than what I paid for it.

Even in jest, it is an attitude that I find distasteful, although I can
understand from where you are coming.

The option for Whelen to repair the unit did not exist (due to its age),
nor do I recall any such marking on the case.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

[Ron Rosenfeld]

On 29 Oct 2004 22:31:42 GMT, Mike Spera > wrote:

>But, if Whelen won't do the repair and will still offer repair
>assistance, they are better than many outfits that just tell you to buy
>a new unit. Good to hear you were able to get it working.

I don't know if the assistance was company policy or one technician trying
to help out. There was no hemming and hawing, so I tend to believe it was
company policy at that time.

The repair was done about 7 or 8 years ago. At *that* time it was over 30
years old. During the past year or so I'm starting to hear a very faint
"siren", but not anywhere as annoying as when I fixed it.

Pretty good return on investment.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

[Jonathan Goodish]

In article >,
Jonathan Goodish > wrote:
> Everything is fine, except that the wing tip strobes can be heard like a
> siren in the headsets. The siren sound is also occasionally transmitted
> over the radio when we make transmissions, because I have been told to
> "check my ELT" after making transmissions. Here are my observations:


Thanks to everyone for your suggestions. I believe that I have located
the main problem right now, which is a local ground at the intercom
jacks in the front panel. The jacks were supposed to be installed using
insulating washers, with a central ground. It looks like the avionics
shop may have done it that way, but then someone replaced the insulating
washers on some of the jacks (but not all of them) with huge lock
washers at some point after the system was installed. After trying
other suggestions, I decided to focus on the intercom system and pulled
the jacks from the panel... the strobe noise (and every other noise)
immediately disappeared when the local ground was broken.

Now, I need to find somewhere to get insulating shoulder and flat
washers, unless someone has another interim solution. Radio Shack
doesn't carry that kind of stuff any more, and don't seem to be able to
find any local retail electronics shops. Don't know whether Lowe's or
Home Depot would carry stuff like that or not, but I doubt it.



JKG

[David Lesher]

Jonathan Goodish > writes:


>Now, I need to find somewhere to get insulating shoulder and flat
>washers, unless someone has another interim solution. Radio Shack
>doesn't carry that kind of stuff any more, and don't seem to be able to
>find any local retail electronics shops. Don't know whether Lowe's or
>Home Depot would carry stuff like that or not, but I doubt it.


DigiKey

3069K-ND may be the right number.

--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

[Jonathan Goodish]

In article >,
David Lesher > wrote:
> >Now, I need to find somewhere to get insulating shoulder and flat
> >washers, unless someone has another interim solution. Radio Shack
> >doesn't carry that kind of stuff any more, and don't seem to be able to
> >find any local retail electronics shops. Don't know whether Lowe's or
> >Home Depot would carry stuff like that or not, but I doubt it.
>
>
> DigiKey
>
> 3069K-ND may be the right number.

Thanks, I believe that I can find the appropriate parts there. Only
problem is, they're showing an end-of-November ship date. I can
probably fabricate something for the interim if I end up ordering from
them.



JKG

[Aaron Coolidge]

Jonathan Goodish > wrote:
: Thanks, I believe that I can find the appropriate parts there. Only
: problem is, they're showing an end-of-November ship date. I can
: probably fabricate something for the interim if I end up ordering from
: them.

If you order new jacks from one of the aircraft supply houses they usually
come with insulating washers. If the jacks are 10 years old you could
proably use new ones anyway, as the springiness of the contacts is probably
mostly gone. I ordered some from Chief aircraft and they were $5 or so for
the jack, washers, nuts, etc.
--
Aaron Coolidge

[Jonathan Goodish]

In article >,
Jonathan Goodish > wrote:
> Thanks to everyone for your suggestions. I believe that I have located
> the main problem right now, which is a local ground at the intercom
> jacks in the front panel. The jacks were supposed to be installed using
> insulating washers, with a central ground. It looks like the avionics


It looks like I spoke too soon, maybe. After looking a the Sigtronics
instructions again (pulled from their web site), it looks like they _do_
recommend a local ground for the headphone jacks, and a central ground
for the mic jacks. Therefore, Sigtronics only supplied insulating
washers for the mic jacks, and the headphone jacks were grounded locally
as directed in the instructions.

My question is, could this still be my problem? Should I go to the
trouble of pulling the airplane apart and running the headphone ground
back to a central point, or is something else most likely the culprit?



Thanks,
JKG

[Ray Andraka]

Try Mouser Electronics http://www.mouser.com. They don't charge a minimum
order fee, which is nice for small quantity buys.

Jonathan Goodish wrote:

> In article >,
> David Lesher > wrote:
> > >Now, I need to find somewhere to get insulating shoulder and flat
> > >washers, unless someone has another interim solution. Radio Shack
> > >doesn't carry that kind of stuff any more, and don't seem to be able to
> > >find any local retail electronics shops. Don't know whether Lowe's or
> > >Home Depot would carry stuff like that or not, but I doubt it.
> >
> >
> > DigiKey
> >
> > 3069K-ND may be the right number.
>
> Thanks, I believe that I can find the appropriate parts there. Only
> problem is, they're showing an end-of-November ship date. I can
> probably fabricate something for the interim if I end up ordering from
> them.
>
> JKG

--
--Ray Andraka, P.E.
President, the Andraka Consulting Group, Inc.
401/884-7930 Fax 401/884-7950
email
http://www.andraka.com

"They that give up essential liberty to obtain a little
temporary safety deserve neither liberty nor safety."
-Benjamin Franklin, 1759