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magnum s-680 receive problems need help please

johnecashflo

johnecashflo

Wish I Was Here
Mar 26, 2007
129
4
28
INDIANA
ok here we go magnum 680 tx works fine no problems there..rx works but is very weak.rf gain knob has little to no effect on white noise also can switch between dummy load and antenna and the white noise level will not change..replaced tr 17 around the rf gain pot inside radio no help and the pot on inside has no effect on white noise either..was probing that area for voltage and when certain legs where touched it showed 6 volts and the noise level went up.im thinking diode but I don't know where to start.ive looked at schematic but im not a elec.tech and I get lost in all the lines..
 

johnecashflo said:
ok here we go magnum 680 tx works fine no problems there..rx works but is very weak.rf gain knob has little to no effect on white noise also can switch between dummy load and antenna and the white noise level will not change..replaced tr 17 around the rf gain pot inside radio no help and the pot on inside has no effect on white noise either..was probing that area for voltage and when certain legs where touched it showed 6 volts and the noise level went up.im thinking diode but I don't know where to start.ive looked at schematic but im not a elec.tech and I get lost in all the lines..
Click to expand...
just to let everyone know it was a diode d-16 was shorted
 
just as a place to start, check the RF gain pot itself, to make sure it's working.

find J108 which is a connector on the front of the PC board. it is a big connector and you will probably find two plugs in it.
pull out the three wire plug that goes to the RF gain pot, and stick a small component lead in to each hole in the connector.
this will allow you to touch your ohm meter to each leg of the Rf gain pot and make sure the resistance is changing as you turn the pot.

once you know the pot is working, it's time to trace the RF from the antenna socket through the RF amplifier (TR17) and see where you are losing your signal.

this will be difficult without an oscilloscope, but if you don't have one, you may just have to start checking individual components using the "shotgun" approach.

right now i am wondering if L6 is good. it can be removed from the board and checked for continuity across it's coils.

just some ideas.
LC
 

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