UBC780XLT

[smithy959]

My faithful 780 has gone deaf on the Military Airband Channels only faint signals that once of a day were strong,
the Civil Airband is OK, are there any pots that need cleaning or tweaking to get back those channels by the way
the signal meter shows a good strength but the audio is very weak and scratchy and wont stop the scan I have
to sit on the frequency to hear it, any help most appreciated.

Thanks:-Ian

 

[Ubbe]

My faithful 780 has gone deaf on the Military Airband Channels

The UBC780 have one filter for the 175-310MHz range and another one for the 310-510MHz range. If it only sounds bad in either band it could be a switch diode that has gone bad.

There are two different crystal filters being used depending on the frequency being monitored, one 244Mhz that are only used for the 310-510MHz range and a 380MHz filter for all other frequency bands. So if it is only 310-510Mhz that are bad then it could be that 244MHz crystal filter that needs to be replaced. It should be marked with FT1 on the circuit board.

Crystal filters usually doesn't shortcircuit to ground when they go bad so you could solder a jumper between its input and output pin to check if it restores reception. It will no longer work as a filter so you will receive a lot of other signal in the band so it is probably not a permanent solution, depending of how much other signals you receive. If you only scan fixed channels and do not do search it might not be so bad.

/Ubbe