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Mid-East Nebraska | electrical/electronic system emits an electrical noise that conducts into radio antenna lead.
reception and minimize static or noise problems, it is important to know what could be causing the problem. These following items may be responsible for many of the noise sources. This list is meant to help identify those sources and offer possible solutions.
Antenna ground cable: A new antenna cable with a ground strap, which must be grounded to operator enclosure (ROPS) frame, has been adopted. A new cable went into production at the following serial numbers: 7600 (002949- ), 7700 (002590- ), 7800 (004828- ). Tractors built prior to listed serial numbers should have antenna cable replaced. A cable kit (RE55196) is available through service parts with instruction for installation. If a customer complains that his radio sounds like it is shorting out or it has intermittent static, tractors should be checked to ensure that antenna cable is not touching antenna stud under the roof enclosure. Ground cable should be banded to antenna cable to prevent cable from contacting antenna post.
Prior to fastening down cab roof with antenna in place, check distant AM and FM stations, or ones with weaker signals in your area.
Antenna lead to radio: Poor radio reception may be the result of an "open" in antenna cable. Replace cable if a continuity check shows cable to be bad.
Blowers, Tach, or onboard controllers: Poor AM reception or noise may be caused by blowers, tachometer, CCU, HCU, PCU or PST transmission solenoids. FM stations may have static or fade in and out. To improve or eliminate this problem, remove capacitor from antenna ground cable. The capacitor is encased in black shrink tube near grounded end of cable. Doing this lowers impedance in ground strap, which reduces noise conducted into radio.
NOTE: Removing capacitor requires that radio be grounded at same place that antenna is grounded to prevent unwanted ground loops. Cut radio ground wire (black, circuit 050) in tractor harness and splice in a 16 GA wire to end lead from radio. Route new wire through same hole as antenna cable and ground at same point as antenna ground (left cap screw holding window bracket to ROPS). Crimp an 8mm-ring tongue terminal onto wire and fasten under cap screw.
After completing first 3 steps, and noise is still interfering with radio, check the following items to diagnose other problems:
a. A/C blower induced static or whine on AM radio: If static or whine is present when blowers are on, determine if interference is from fresh air blower or circulation blowers. Fresh air blower is located under right front corner of cab and two circulation blowers are under seat. Isolate fresh air blower by disconnecting its wiring harness located behind battery box and just below horizontal portion of exhaust pipe.
If interference disappears, then install RE62490 capacitor (check with DTAC for parts availability) to blower harness. If fan interference is still present after disconnecting fresh air blower, the problem is with one or both circulation blowers. These blowers have noise suppressors but may require an additional interference suppressor. Install GM part no. 3906145 (obtain from GM dealer) on power lead to problem blower(s). Ground suppressor using a blower mounting screws assuring a good clean connection to sheet metal. Blower suppressors were installed in wiring harness prior to the following serial numbers and in motor housing across power leads after serial numbers: 7200 (002329- ) 7400 (002649- ) 7600 (005796- ) 7700 (006872- ) 7800 (009826- )
b. Alternator noise or whine on AM radio: This noise usually increases in pitch with engine speed. A filter (GM part number 1224205) available from a GM dealer may suppress alternator noise. Install filter in +12 volt battery lead (light green color) between connector and radio and ground to stud on rear of radio chassis.
c. Tachometer noise on AM radio: Static on radio from lamp test in instrument panel may be present a few seconds after key is turned on or tractor startup. The radio static should stop after lamp test (within 3 seconds). If it does not, verify Tach is noise source by pulling fuse. If that eliminated static, noise is being conducted from Tach to radio through circuit 134. This wire can be removed from tachometer harness but will prevent radio light from dimming when tractor lights are switched on.
d. Electric fuel pump noise on AM radio: On 7700's ( -003109), radio static may be caused by electric fuel transfer pump. The noise is a pulsing static and increases in frequency with engine speed. Install a RE54918 suppressor harness in series with harness to pump to eliminate static.
e. Hitch noise (when lowering or raising) on AM radio: Radio static may be present on some tractors when lowering and raising hitch. The noise will remain when hitch is left in down position. Refer to solution 55274 for adding a noise suppressor to eliminate noise.
f. Onboard controller static on AM and FM radio: If radio noise is not caused by any of the other things listed, and an AM/FM station can be picked up with key in accessory position, then radio noise may be caused by one of the three onboard controllers (CCU, HCU or PCU). Isolate noise by pulling fuse for each controller one at a time or combination thereof (CCU - fuse 4, HCU - fuse 5, PCU - fuse 6). If noise is caused by CCU (fuse 4), then replace with new RE61858 (CCU II) to reduce electromagnetic noise. For tractors prior to serial numbers 7600-005366, 7700-006400, 7800-008363, which have electronic clutch cooling, replace with RE64602. Static from either HCU or PCU will have to be addressed on an individual basis through DTAC.
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FM Radio Recption in Tractor
