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bbradburry(at)verizon.net
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 Posted: Fri Sep 25, 2015 4:54 am Post subject: Request for some direction and advice |
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Well, here is an update to the sad state of affairs with the radio/autopilot.
I found last Saturday that the problem was worse than it had ever been. Every time I keyed the mike, either the autopilot or the radio or both would power off, along with a lot of clicking in the headset. So I rigged up a separate coax and a separate antenna and tried transmitting through that setup. It didn’t seem to make any difference. The problem was still the same.
So I decided to try and find a local radio shop to take the plane to for them to check out. I contacted a couple of them and both told me that it sounded like a high resistance connection in either the power or ground circuit. By the way, I don’t think I have mentioned that both these units are on the E-buss.
So yesterday I went out and used a couple of VOM meters to see what the voltage did when I keyed the mike. I had one meter on the E-buss fuse block radio power wire just after the fuse and the ground connected to the radio back plate. The other meter was connected similarly to the autopilot.
I couldn’t get the problem to appear! Everything worked fine! No fricking clicking! The voltage would drop to the range of low 11 volts during transmission on both units. Turning on the E-buss diode bypass improved this by about a half volt. I put the batteries on charger and the voltage would hold around 12 volts.
The meter that was connected to the autopilot had shorter leads and as a result it was physically closer to the radio. When I keyed the mike, this meter would usually go up to 15. 17. and even once to 20 volts. One of the radio shop guys told me that was caused by the radio and was not true voltage. This sounds like it may be proof that Bob is correct about RF leakage?
Bottom line is that the radio and autopilot have (probably temporarily) fixed themselves. I doubt that this is permanent so further advise would be appreciated.
Thanks,
Bill
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Bill Bradburry
Sent: Thursday, September 03, 2015 11:52 AM
To: aeroelectric-list(at)matronics.com
Subject: RE: AeroElectric-List: RE: Request for some direction and advice
Ok, I will report after I know more of what I have fixed..I am wildly optimistic at this point!
I did check the coax connector at the antenna and it seemed solid. I really have no way to check the potted box at the antenna, but I do have a spare antenna just like it that I could try if necessary. I also have a piece of RG-400 about 10 ft long with connectors on both ends that I can try with both antennas.
Bill
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Robert L. Nuckolls, III
Sent: Thursday, September 03, 2015 10:06 AM
To: aeroelectric-list(at)matronics.com
Subject: RE: AeroElectric-List: RE: Request for some direction and advise
At 11:27 PM 9/2/2015, you wrote:
Sounds like the project is moving forward again.
Great! Let us know what you discover. As I recall,
we still have a receiving noise issue that MIGHT
be related to the antenna connector . . . but
probably not. We can tackle that one after
you've had more time to assess the state of
your universe.
Bob . . . | Quote: | | http://www.matronics.com/Navigator?AeroElectric-List |
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[quote][b]
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user9253
Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan
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| Posted: Fri Sep 25, 2015 7:09 am Post subject: Re: Request for some direction and advice |
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The vast majority of electrical problems are caused by bad connections. Those bad connections will be easier to find when the circuit is heavily loaded. I suggest that you connect a high wattage lamp in parallel with the problem avionics (using the same +12 volt and ground connections as the avionics). Then measure the voltage across the lamp. It should be pretty close to battery voltage. If not, then use the positive battery post as a reference and measure voltage drop along the positive half of the circuit. Then use the negative battery post as a reference and measure the voltage drop along the grounded side of the circuit.
If all is well with the DC power, then check the radio antenna. Is the radio fully seated in its tray?
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Joe Gores |
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skywagon
Joined: 11 Feb 2006
Posts: 184
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| Posted: Fri Sep 25, 2015 8:36 am Post subject: Request for some direction and advice |
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Joe is so right on this problem and his suggestion is the way to go. You
need to push current thru the wiring path to find the flaw.
While doing his method of checking for voltage drops, reach in and
bump/jiggle all connections associated with the path being measured. And,
lastly, read his last line again.
This radio and tray thing/problem has been covered in the past. Again, one
example is the Garmin 430 Navigators, etc. If the tray is bolted in
"slightly" behind the planes "panel", then when the radio is inserted it
will NOT fully seat with all the connectors in the rear of the tray.
Because. . . the radio and its bezel during insertion is stopped at the
front panel. And, thus it will never be fully seated. Randomly, the radio
will loose a connection and go haywire. Fix is. . to remove the radio,
unbolt the chassis tray and pull it forward to be even or maybe a tad (
1/16" )forward of the front panel and rebolt it in place.
D. Lloyd
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bbradburry(at)verizon.net
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| Posted: Fri Sep 25, 2015 12:36 pm Post subject: Request for some direction and advice |
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Regarding the radio being seated in the tray.
The tray was mounted just slightly proud of the panel. I then made a bezel
to go around the radio stack. When I made the bezel, I tried to fit it
around the top item in the stack which is a KMD150 moving map. I didn't do
such a good job of fitting this bezel opening so I decided to place the
bezel under the faceplate of the rest of the stack. This included the radio
and the transponder. I realized this was a possible problem during this
recent search and I opened the bezel up so that all the items in the stack
could fit inside it. This seated the radio an sdditional 1/8 inch and as a
result, the problems with the engine going haywire during transmit went
away. This caused me to think that I had solved the problem. Apparently,
not so fast!
What ever this problem is, it is very intermittent. After reseating the
radio, and the problem going away, the problem came back worse than it has
ever been. Now, the last time I tried it, the problem has gone away again.
Regarding the suggestions below.
The avionics and ground connections end with a pin in a connector. I am not
certain how I would connect a high wattage lamp in this circuit. Are we
talking about like a landing light? Would this blow the fuse? How close is
pretty close to battery voltage? If I checked the voltage at incremental
steps in the circuit, what should I expect to see? Will the voltage drop a
tenth or so volts at each connection? Or not much at all?
I know I sound like a total idiot about electrical stuff, but unfortunately,
what you hear is what you get. :>(
When the problem was presenting itself I tried a different coax and a
different antenna. I didn't see any change in the effect. Unless the
problem is in the radio backplate or radio itself, I am not certain that it
is an RF leak. However, I am also pretty certain that there is enough of an
RF leak to cause the meter to go haywire even if the other stuff does not.
Bill
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user9253
Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan
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| Posted: Fri Sep 25, 2015 3:35 pm Post subject: Re: Request for some direction and advice |
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A landing light would probably blow the fuse. How about an automotive brake light? A bigger fuse could be installed temporarily for a few minutes while testing. If a bad power connection is causing the autopilot to shut off, I would suspect that the bad connection is located between the bus and battery. If the radio power connections are not readily available, then test at the closest point that is available. The total voltage drop from the battery to radio should not be more than a few tenths. And that drop should be spread evenly over the entire circuit, not concentrated at any one connection. Do the voltage measurements suggested in my previous post while keying the transmitter.
Are you sure that the battery is good? 11 volts is way too low. It should be closer to 13 volts, especially with the charger connected. It is normal for the E-bus diode to drop a half volt.
The interface between the radio and its tray are highly suspect. Is there any way to measure the distance between the back of the radio and the back of the tray?
| Quote: | | This sounds like it may be proof that Bob is correct about RF leakage? |
Bob is usually right.
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