BCM lives, radio dies...
10-06-2010, 08:16 AM
#1
BCM lives, radio dies... A little while ago I took out my BCM and did the solder fix that takes care of the random power window/radio failures. I buttoned everything back up and although the windows and radio don't cut out anymore, I now notice that my AM/FM reception is very poor. Is there anything about the BCM that can affect radio reception, or is this just a coincidence? Also, would radio reception quality be based just on the the antenna connections or is there something else down there I might've screwed up while dragging that BCM in and out? Thanks in advance...
10-06-2010, 08:50 AM
#2
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Double check just to make sure your antenna adapter going into the headunit isn't loose. I've done it before when removing the headunit I didn't get the antenna into it enough and it wasn't secure. And I'm pretty sure the antenna doesn't go through the BCM.
10-12-2010, 03:33 AM
#5
Alright so I pulled out as many trim panels as I could and looked for any damaged wiring-didn't find anything. I did notice however, that when I move the actual antenna wire itself the reception started to cut in and out. Once again, there's no visible damage to any wiring, so my question to you electronics/audio guys is this: is it possible for the wiring inside the antenna wire itself to be damaged? Lord knows I've encountered that enough on normal electrical work: the wire looks ok on the outside but is all broken up on the inside...
10-12-2010, 08:32 AM
#6
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This an antenna adapter for an aftermarket headunit? May just need to replace the adapter, or if it's the stock antenna wire it could just need replaced if it's not staying connected properly to the headunit, if that makes sense. I had an issue where the radio signal was poor and the antenna didn't have a good connection to the back of the headunit so I replaced it and had no more issues.
10-12-2010, 08:42 AM
#7
Alright so I pulled out as many trim panels as I could and looked for any damaged wiring-didn't find anything. I did notice however, that when I move the actual antenna wire itself the reception started to cut in and out. Once again, there's no visible damage to any wiring, so my question to you electronics/audio guys is this: is it possible for the wiring inside the antenna wire itself to be damaged? Lord knows I've encountered that enough on normal electrical work: the wire looks ok on the outside but is all broken up on the inside...
You might want to get an antenna extension cable to try it out. Connect it to the antenna and just lay it through the interior to the HU for testing purposes. If you have a factory HU, you will need an antenna adapter to fit the small socket on the back of the HU but the connector at the antenna is standard size.
You can also use a multimeter to test continuity of the cable and for a possible short between the center conductor and the outer shielding. You can even measure approximate impedance of the cable - it should be about 75 ohms along the center conductor (a DC ohmmeter will generally read lower than the rated impedance).
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10-13-2010, 03:32 AM
#8
You can also use a multimeter to test continuity of the cable and for a possible short between the center conductor and the outer shielding. You can even measure approximate impedance of the cable - it should be about 75 ohms along the center conductor (a DC ohmmeter will generally read lower than the rated impedance).
If I have broken the cable I don't understand how it could've happened. I was pretty rough in trying to get the BCM out but I don't see how I could've ruined the antenna cable...Oh well....
10-20-2010, 04:40 PM
#9
Alright, well I put a multi-meter to both ends of the antenna cable and I've got continuity. I was convinced that my bad radio reception was from a broken up cable. Could I have checked the continuity improperly? Is there something else I need to check? If it isn't the cable, then what else could it be?
10-22-2010, 03:42 AM
#11
So, I'm supposed to put the meter onto both ends of the antenna cable on the OUTER shielding only as one test, and then also put the meter between the center and the outer shield as the second test?
What does the numerical value of 1.5 to 2.0 mean? Is that volts? Resistance?
10-22-2010, 07:50 AM
#12
There are several things about an antenna cable that must work properly for the signal to reach the radio.
The center conductor (D) carries the signal and must be continuous from end to end. When you check continuity on the center pin, you're trying to find if the cable is broken... no continuity = broken cable.
The shielding (B) must also be continuous because it carries the ground and provides shielding from electromagnetic interference.
The insulator (C) keeps the signal conductor from connecting electrically to the shielding. Testing continuity between the center pin and the outer shield determines if the insulator has been damaged and is shorting out the cable.
The narrow center pin of the Motorola-style connector on most car antennas is soldered to the center conductor in the cable. The larger outside part of the plug with the spring sides is connected to the cable shielding. When you set your multimeter to ohms (resistance) and touch one probe to each of the center pin and outer case, you should get some very large number or an indicator for infinity (usually -1). If you don't then the cable is shorted and needs to be replaced.
When testing end to end continuity of the cable, the opposite should happen. With the meter set to ohms, touching the probes to opposite ends of the same conductor (i.e. center pin at both ends or the outer shield at both ends) should display a small number or even 0 (depending on scale). An infinity reading (-1) shows that the cable is broken someplace.
Using the continuity tester setting on the meter is even easier. The meter should not beep when testing continuity between the outer and inner conductors but should beep when testing end to end.
The center conductor (D) carries the signal and must be continuous from end to end. When you check continuity on the center pin, you're trying to find if the cable is broken... no continuity = broken cable.
The shielding (B) must also be continuous because it carries the ground and provides shielding from electromagnetic interference.
The insulator (C) keeps the signal conductor from connecting electrically to the shielding. Testing continuity between the center pin and the outer shield determines if the insulator has been damaged and is shorting out the cable.
The narrow center pin of the Motorola-style connector on most car antennas is soldered to the center conductor in the cable. The larger outside part of the plug with the spring sides is connected to the cable shielding. When you set your multimeter to ohms (resistance) and touch one probe to each of the center pin and outer case, you should get some very large number or an indicator for infinity (usually -1). If you don't then the cable is shorted and needs to be replaced.
When testing end to end continuity of the cable, the opposite should happen. With the meter set to ohms, touching the probes to opposite ends of the same conductor (i.e. center pin at both ends or the outer shield at both ends) should display a small number or even 0 (depending on scale). An infinity reading (-1) shows that the cable is broken someplace.
Using the continuity tester setting on the meter is even easier. The meter should not beep when testing continuity between the outer and inner conductors but should beep when testing end to end.
10-25-2010, 11:08 PM
#14
Alright, so testing center to center there's continuity/tone. When I put the meter on to the center and outer shielding I got intermittent tone/numerical values, which leads me to believe that's where the cable is failing. Does it matter if I test the antenna end as opposed to the radio end of the cable? I don't think it would but I thought I'd mention that I tested the antenna side...
10-26-2010, 07:38 AM
#15
No, it doesn't matter which end you test when testing between the inner and outer conductors. They should be continuous but separate conductors throughout the cable so you would get the same result at either end. Since you are showing some continuity between them, there must be a breakdown in the insulation between them somewhere in the cable. That will cause loss of signal. You should replace the cable.
10-27-2010, 03:38 AM
#16
Thanks to your help I finally feel like I'm beginning to see the end of this. Quick question: my local dealership says that this particular cable is no longer available. Is it possible for any car-audio store to fabricate one for me? If not, I think there are some online parts retailers that might be able to get the cable but...at a relatively high cost. Thanks again!
10-28-2010, 07:41 AM
#17
Actually, it's just an extension cable except that it has male connectors on both ends. You can buy antenna extension cables at most audio shops. You'll have to change the female connector to a male one. The connectors are available at Radio Shack so you could do it yourself. You'll also need an adapter for the HU end if you're using a factory HU because GM uses a smaller than standard version of the Motorola plug in their HUs. The adapter is available at any auto parts store or even WalMart.
11-17-2010, 06:49 PM
#18
I haven't been able to deal with this cable issue until now. I can't believe that no one in San Diego has a male to male cable extension, or at least the adapter that would allow me to plug into the smaller jack into the factory HU. I did find a traditional male to female cable, and I guess I could buy the male connector and change the female connector to a male one, but how do I do that? Is it similar to splicing wires, needing only a crimp and solder or something? This is giving me a headache. Another idea I had was finding the short/break in the original extension cable, cutting it out and rejoining the cable-is that a viable solution?
11-18-2010, 07:57 AM
#19
Radio Shack carries the male Motorola plugs in both crimp-on and solder versions (the solder version is more work but gives a better connection). Instructions are included with the plug but basically you strip the insulation about 3/4" then cut the outer shielding about halfway so you can expose the center conductor. Then shove it in the plug and crimp or solder.
That will give you an antenna cable with male plugs at both ends. If you're using a factory head unit, you'll still need an adapter to convert to the smaller plug used by GM. The adapters are available at audio shops, auto parts stores, and even WalMart. Make sure you get the one with a standard size female socket connecting to a small size male plug - they also make them the other way around for connecting a GM antenna to an aftermarket head unit.
That will give you an antenna cable with male plugs at both ends. If you're using a factory head unit, you'll still need an adapter to convert to the smaller plug used by GM. The adapters are available at audio shops, auto parts stores, and even WalMart. Make sure you get the one with a standard size female socket connecting to a small size male plug - they also make them the other way around for connecting a GM antenna to an aftermarket head unit.
11-18-2010, 01:32 PM
#20
Alright, then that's what I'll have to do. I even e-mailed Crutchfield, asking about adapters and whatnot, and they told me to do a google search, on "google.com," f**king idiots. I can't believe how much of a hassle this is; you can do a H/C/I swap in less time than it takes to for this cable thing...
They have this adapter set that features either a male or female main plug, that splits into 8 or so different wires that fit different car brands. Pretty bulky but convenient. All I have to do is give my new extension cable a connector change on one end...
They have this adapter set that features either a male or female main plug, that splits into 8 or so different wires that fit different car brands. Pretty bulky but convenient. All I have to do is give my new extension cable a connector change on one end...
Last edited by myk; 11-18-2010 at 01:38 PM.