| Author |
Message |
    
P.Anderson
| | Posted on Wednesday, October 08, 2003 - 9:18 pm: | 
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Hello!
I have an President Lincoln cb radio and i refuse to transmit.
The sign Tx lights up but no reaction on the Rf power meter.
could it be MRF-477 that is gone or could it be some Tx sw transistor or the IC 104 on the board.
I have tried to force Tx sw on the board with a jumper when i do this i get some readings on the Rf meter
and the cooler fins gets hot.
Please if you could give me some hints of what could be wrong i ´would be very happy.
I really want my old rig to work again.
Best regards
P.Anderson
SWEDEN
p,s sorry for my bad English :-) |
Bruce
| | Posted on Wednesday, October 08, 2003 - 10:17 pm: |
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do you have a schmaitc? if not i can send you one |
ss8541
| | Posted on Wednesday, October 08, 2003 - 11:15 pm: |
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the ptt goes to the cpu and then the cpu toggles the tx/rx switching circuits. if it is showing tx on the display, then we know that the ptt is getting to the input of the cpu. but we do not know if the output of the cpu is toggling or if there is a broke trace or colder solder joint somewhere between the cpu and the tx/rx switching circuit.
since it seems that you can make the radio tx by manually jumpering the circuit, then i would 1st look for broken traces, bad wiring, or cold solder joints. this is about all i can give you for now. i am at home, and my schems are elsewhere.
-if- you have a schem, find where the output of the cpu ic chip feeds the tx/rx(ptt) line. with a volt meter, see if this leg toggles voltage when the ptt is pressed. if so the cpu is fine. i have seen cpu's blown in the past when voltage was added to the mic ends ptt line. when that happened, i am pretty sure that the tx symbol would not come on at all but i can't say for sure. so it may be the cpu or it may not. if the output of the cpu toggles, then it is not the cpu. |
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