Cherokee Strobe Noise

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

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)

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

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

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

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

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

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

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

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