The CQ uses a Fuba Beta-flex D amplified roof antenna similar to the style used on some VWs of the same era (most notably the 16V cars). The 90Q20V uses antennas that are embedded in the front and rear glass. I believe at least one of them is amplified, so much of the troubleshooting info here would be applicable on that system, too. One obvious difference you'll notice is that the 90Q20V has two antenna cables going into the head unit. The following Fuba troubleshooting tips were shamelessly swiped from Jay's Aktiv Audiophile Page.
If you have problems with radio reception don't be quick to blame the head unit; the problem my lie with the radio antenna. The OEM factory antenna employs separate amplifier circuits for the AM and FM bands. These circuits are designed to boost the most radio signals possible while filtering out unwanted stations and noise. These microelectronic circuits are housed in the antenna's base while the receiving element consists of a spring loaded, wire-wound, fiberglass mast designed to withstand most automatic carwash machinery.
Symptoms of problems with radio reception include poor FM reception (only strong stations tune in), and virtually no AM reception. Other indications of faulty antenna operation include audible "pops" heard on the AM band originating from turn signal or windshield wiper relays. The culprit to these problems may be that the antenna is not getting 12 volt power, the antenna is poorly grounded, or the antenna amplifier may be bad. The worst case scenario is that none of these problems is the cause and the radio itself is bad. If you have an aftermarket radio, the antenna may not be receiving power or you may have an ill-fitting antenna RF cable adaptor. Regardless, to troubleshoot for the source of the cause will require gaining access to the antenna and power connections at the back of the head unit and at the base of the antenna.
To gain access to the connections at the back of the stock head unit, follow the instructions for removal in the Head Unit Replacement section above. If you have an aftermarket unit, refer to the owner's manual for proper removal procedures. The antenna RF cable is a thick black cable. The antenna remote power-on lead that supplies 12 volt power is a white wire that comes out of the black connector. There will be two white wires going into the same slot on the black connector--one is power for the antenna, and the other is power for the rear speaker amps. To access the base of the antenna, you only need to remove the interior dome light above the rear seats. The power and RF leads extend from the antenna amplifier unit through the mounting nut and connect with the power and RF cable that extends from the head unit in front of the car.
Check for obvious corrosion or loose connections at the head unit and at the antenna amplifier. If you have an aftermarket head unit, check to make sure the antenna power lead is connected to remote power-on. Additionally, Audi uses a DIN-3 RF cable connector which may require an adaptor to connect with an aftermarket unit. If an adaptor is used, make sure it fits properly and that the connection is secure.
With the power off, use an ohmmeter to make sure the contact nut is grounded to the chassis. Continuity check (i.e., test for a short circuit) the contact nut against a known chassis ground. You should read minimal resistance (ohms) or if your meter has a continuity setting, you should hear an audible tone. Otherwise, loosen the nut, clean any corrosion, retighten and recheck continuity.
Use a voltmeter or test light to make sure the antenna is receiving 12 volts. Disconnect the power lead at the antenna. With the head unit on, test for 12 volts between the power lead and the contact nut under the antenna. You should read 12 volts on the meter or the test light should light up. If not, check the power connections at the head unit. In addition, use the voltmeter to verify that the remote power-on is putting out 12 volts at the head unit.
If 12 volt power is verified, check RF cable continuity. Continuity check both the center lead and the ground (the outer metal portion, i.e., the shield) of the RF cable separately. That is, check the center lead of one end of the cable to the center lead of the other end of the cable. Test the ground in a similar manner by checking the shields at both ends of the cable. To test for a short circuit between the RF cable center lead and ground, check the center lead against the shield at either end of the cable. If the center lead or ground lack continuity, or if there is a short between the center lead and the shield, then the RF cable is damaged and may be crushed or crimped cable along the route to the radio. Verify continuity with the shield and chassis ground. If there is no continuity, then the RF cable is not connected to ground.
Lastly, test the head unit itself for proper operation with a standard rod antenna on a short cable. Ground the antenna if possible. Another quick and dirty test is to pull the radio and plug it into another Audi with either an amplified antenna or standard antenna. The power and speaker wiring harnesses are similar across Audis and VWs.
If the radio lacks a power antenna lead, connect the power lead from the antenna to the accessory side of the fuse block, or tap into the power line going to the radio if it is switched by the ignition/accessory position. The amplifiers in the antenna draw approximately 30 mA which can drain a battery if left on for extended periods while the car is parked. To minimize RF noise, avoid running the RF cable along or next to high-current-draw cable such as power leads for speaker amps, etc.
If the radio checks out and all ground and power connections are good, then the antenna amplifier unit needs to be replaced. The FUBA unit retails for around $120-$130 at the dealer (P/N 445 051 503). The OEM FUBA is available through several aftermarket sources such as Antenna World, Rapid Parts, Euro Sport, etc. for around $55-$90, and some places will also sell replacement parts such as the mast or the rubber gasket between the antenna base and the car's roof. Note that the OEM FUBA has a different mounting post than the factory unit. The OEM unit has a round flange where as the factory unit has a square flange that prevents rotation. Also note that both amplified and non-amplified OEM units are available so make sure you order the amplified one that is usually denoted as model #17237. Mounting instructions are included with the unit and are fairly straightforward and easy to follow.
Precautionary Tips:
To minimize potential damage to the antenna amplifier, turn off the radio and thus the power to the antenna when working with electrical connections to the car. This includes the instances when the car is taken in for service. When removing the antenna mast, again turn off the power first. I am unable to comment if the antenna amplifiers are designed to operate without the resistive load that the mast provides, so as a preventive measure, do not operate the stereo without the mast in place.
