Trio TS-780 Repair
 

Hello all,

I just got a Trio TS-780, however there is no RF power on Transmit. At
first i thought that PA stage was damaged however i also noticed that
the ON AIR Led and Antenna Switch are not energised in Transmit Mode.
Receiver is working perfrectly. Can anyone supply me with detailed
schematics for this Transciever and whether anyone has seen this fault
on similar transceivers?

Thanks

Mario

Trio TS-780 Repair
 

"MerLin" wrote in message
oups.com...
Hello all,

I just got a Trio TS-780, however there is no RF power on Transmit. At
first i thought that PA stage was damaged however i also noticed that
the ON AIR Led and Antenna Switch are not energised in Transmit Mode.
Receiver is working perfrectly. Can anyone supply me with detailed
schematics for this Transciever and whether anyone has seen this fault
on similar transceivers?

Thanks

Mario


Mario -

Always have a 50 ohm dummy load attached for testing.

Check the T/R (Transmit/Receive) relay in the RF section of the radio.
Is it working?

Kenwood/Trio TS-870 Repair Notes (check for shorted capacitor)
http://www.mods.dk/view.php?ArticleId=3094

Kenwood/Trio TS-780 Owner and Service manuals are he
http://www.mods.dk/view.php?ListManuals=kenwood

Greg
w9gb

Trio TS-780 Repair
 

Hello Greg,

Thanks for your reply. I have just downloaded the user and service
manual for the TS-780..i will give it a look later on. However as for
T/R switch...i don't think it is being activated on trasmit as i don't
hear any replay operation. So it seems that part of the control
circuit is not functioning. I still have to look at the schematics
though.

Thanks for you help

Mario

gb wrote:
"MerLin" wrote in message
oups.com...
Hello all,

I just got a Trio TS-780, however there is no RF power on Transmit. At
first i thought that PA stage was damaged however i also noticed that
the ON AIR Led and Antenna Switch are not energised in Transmit Mode.
Receiver is working perfrectly. Can anyone supply me with detailed
schematics for this Transciever and whether anyone has seen this fault
on similar transceivers?

Thanks

Mario


Mario -

Always have a 50 ohm dummy load attached for testing.

Check the T/R (Transmit/Receive) relay in the RF section of the radio.
Is it working?

Kenwood/Trio TS-870 Repair Notes (check for shorted capacitor)
http://www.mods.dk/view.php?ArticleId=3094

Kenwood/Trio TS-780 Owner and Service manuals are he
http://www.mods.dk/view.php?ListManuals=kenwood

Greg
w9gb

Trio TS-780 Repair
 

Has the wiring in the microphone been checked? Maybe it's simply a
broken PTT line inside the mic or at the connector end...

Scott



MerLin wrote:

Hello Greg,

Thanks for your reply. I have just downloaded the user and service
manual for the TS-780..i will give it a look later on. However as for
T/R switch...i don't think it is being activated on trasmit as i don't
hear any replay operation. So it seems that part of the control
circuit is not functioning. I still have to look at the schematics
though.

Thanks for you help

Mario

gb wrote:

"MerLin" wrote in message
groups.com...

Hello all,

I just got a Trio TS-780, however there is no RF power on Transmit. At
first i thought that PA stage was damaged however i also noticed that
the ON AIR Led and Antenna Switch are not energised in Transmit Mode.
Receiver is working perfrectly. Can anyone supply me with detailed
schematics for this Transciever and whether anyone has seen this fault
on similar transceivers?

Thanks

Mario


Mario -

Always have a 50 ohm dummy load attached for testing.

Check the T/R (Transmit/Receive) relay in the RF section of the radio.
Is it working?

Kenwood/Trio TS-870 Repair Notes (check for shorted capacitor)
http://www.mods.dk/view.php?ArticleId=3094

Kenwood/Trio TS-780 Owner and Service manuals are he
http://www.mods.dk/view.php?ListManuals=kenwood

Greg
w9gb

Trio TS-780 Repair
 

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

Trio TS-780 Repair
 

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