4dtv receiver
Repairing a Mis-tuned UHF Can


Disclaimer
Warning this info is only for authorized service people.... If you attempt this procedure, it will be done at you own risk. Doing this procedure will void all warranty unless being done by an authorized professional / repair center. Myself or anyone affiliated with this website, and GI/Motorola accepts no responsability for this repair, and anyone doing this repair shall be at fault of any and all damage occured while trying to make adjustments, and there after.


The following is a quick remedy of a failure in the 4Dtv UHF remote control section, for the 920 and 921 models. If your 4Dtv is working properly via infrared remote control, and you have determined that the UHF address matches on both the remote control and the IRD, then the following procedure may eliminate the problem. PLEASE NOTE- if you are not comfortable working with board level components you should return the receiver to General Instrument for warranty repair.
The likely cause of the failure is the tuned UHF reception "can" that is attached (internally) to the UHF whip antenna. The UHF can is, essentially, a radio receiver. What has happened is that the frequency of the receptor has drifted or was improperly set at the factory. Over time, some of these reception cans may have become mistuned. The following procedure will help a qualified technician to reset the UHF can to the right frequency. Make sure you disconnect the AC power before attempting to service the unit.

Procedure


  • Unplug the 4DTV.
  • Remove the top cover of the receiver by removing the four torx screws on the sides.
  • Locate the UHF "Can" in the right rear of the unit as viewed from the front. See Illustration 1 for help in identifying the UHF "Can."
    Illustration 1

 
Illustration 1
  • Using a pair of pliers, carefully straighten the tabs holding the top of the UHF can in place. Remove the cover to the can. See Illustration 2.

    Illustration 2

 
Illustration 2
  • Inside the UHF "can" you will see a small printed circuit board. On that board are two coils which set the reception frequency. The white arrow points to the two coils. See Illustration 3

    Illustration 3

 
Illustration 3
  • An adjustment must be made to the last loop of the lower of the two coils to bring the UHF receptor back to the right frequency so it can respond to the hand held remote control signals. You should use a non-conductive i.e. plastic tuning tool (diddle stick) to spread the last turn of this coil about 1/8th of one inch. See Illustrations 4 and 5.

    Illustration 4

 
Illustration 4

Illustration 5

 
Illustration 5

  • You are now ready to test the frequency. Being careful to shield the unit from the infrared commands, see if the receiver now responds to the UHF remote control. You may have to make small adjustments in the spacing of the coils for best reception. Once reception is established, replace the cover of the UHF remote control can. Reattach the top cover of the IRD and reinstall into the system. Be very careful while testing the 4Dtv during this stage. There is live AC voltage in the receiver, do not touch any thing with your bare hands. After you've tuned the can, remove the AC power cord before you re-assemble the 4Dtv.