Hi Scott,

Yeah it has been checked and it was found to be correct. The TS-780
also has a Send/Rec Switch on the front panel and when it is flicked in
Send Mode, it goes in transmit mode ( no reception is possible) however
ON AIR LED does not switch on, T/R relay not activated and no RF power
output. Furthermore, i believe that when TX offset is activated, the
display frequency should change ( depedning on the offset frequency) on
transmit. However this does not change. It seems that in transmit
mode, the transmitter is not being activated at all.....that is why i
presume its a control failure rather than RF or final stage failure. I
am currently following the logic control circuit to switch between
transmit/receive mode.

Thanks for your help though. If anybody has more suggestions, please
let me know. Thanks all

Mario

No problem!! I just wanted to make sure the simple stuff was ruled out
first =8O

Sounds like you're on the right track. Assuming you have a schematic,
just start following the PTT line from the mic jack until you hit a
logic gate or a transistor. One of those is likely to be used as a
switch that routes some DC voltage to the tx circuits and maybe labeled
something like T9V or TX9, indicating some voltage level for TX mode.
Once you find the (probably a transistor) device being used as the power
switch for the transmit sections, check the capacitors and resistors
connected to it for shorts or opens. Is it possible there are 2 power
supply sections and one side (transmit) is dead?

Scott



MerLin wrote:
Hi Scott,

Yeah it has been checked and it was found to be correct. The TS-780
also has a Send/Rec Switch on the front panel and when it is flicked in
Send Mode, it goes in transmit mode ( no reception is possible) however
ON AIR LED does not switch on, T/R relay not activated and no RF power
output. Furthermore, i believe that when TX offset is activated, the
display frequency should change ( depedning on the offset frequency) on
transmit. However this does not change. It seems that in transmit
mode, the transmitter is not being activated at all.....that is why i
presume its a control failure rather than RF or final stage failure. I
am currently following the logic control circuit to switch between
transmit/receive mode.

Thanks for your help though. If anybody has more suggestions, please
let me know. Thanks all

Mario