Originally Posted by TimRogers
Since we are bringing this thread back up, I'd like to bring up an FM noise problem I have in a '93 Nissan with a '90's or early 00's Kenwood head unit (KDC-S2009).
- The CD works fine with no noise; if I pause it with the key at "accessory" or "on", there is no noise.
- With middle strength to weak FM stations, they come in clearly with the key at "accessory" but when the key is turned to "on", noise drowns out the FM program, even without the engine running. The noise continues with the key in "on" after the fuel pump has shut off and if I disconnect the ignition coil.
I've had this issue ever since I got rid of the stock radio in the late 90's with another Kenwood that had this same issue.
The ground wire is connected to a bracket that holds the airbag computer.
The rear ground port and the mounting bracket are each grounded to separate bolts that hold the shifter assembly to the chassis of the car.
All three locations show good grounds (multi-meter run between the hot lead to the power port and ground shows 12.xx volts).
I recently had the antenna off when I was doing bodywork and made sure the mounting points for it were corrosion free.
So, who has ideas?
You need to ground the antenna to the chassis, not a shared bolt. Also, using DC to measure ground for an RF tuner is pointless. The fact that separate bolts are being used makes a big difference- each has a different path to ground.
One thing I don't seen any mention of is the battery ground- the body is grounded to the battery near the negative post and this is the point where ALL of the electrical circuits connect to the battery. Sure, the engine is grounded through the battery cable but the engine compartment is also bonded
to the engine and battery- if the engine has had major work done to it, it's possible that whoever worked on it removed the braided wire from the engine to the firewall. Also, the hood is supposed to be bonded to the firewall- all of this is to prevent RF/EMI from escaping the engine compartment and affecting other cars. If you listen to AM radio and a hot rod passes or pulls up next to you and you suddenly notice a lot of noise in the radio, this is usually because they like to remove those bonding conductors- they don't look pretty, so they need to go.
Speaking of which how is the signal when you listen to AM? If it's non-existent, replace the plug on the antenna cable or replace the antenna- this is the easiest way to find out if you have a bad antenna- AM needs the center conductor more than FM does.