FT-780R model preset by diodes - UK Vintage Radio Repair and Restoration Discussion Forum

Kris_VK3XON · 24th Sep 2019, 9:09 am

I've been restoring a Yaesu FT-780R and a bit stumped with the presetting of model A/B/X diode preset :

I got a 780R with a weird mod, add on board that forces repeater shift to 1.6 MHz UK (I'm in Australia).
Removed the board and repaired the cut tracks (2 x 4 bits), corrected the wiring back to MCU board for +/-/simplex. All good.

So, now it turns out I have a Model B because the unit still starts up on 433 MHz.... but the stock repeater split is now 7.6 MHz (I need 5 MHz). According to the manual Model A is 435 MHz startup and 5 MHz split. (this is what I need).
Looked in the user manual and the only difference I see in the schematic between Model A and B is that A has D10 & D12 whereas Model B has D12 only (my 780R indeed only had D12 soldered).

So I added D10 which should turn it into Model A, however it becomes a Model X (starts up 445 MHz). I CANNOT find any other difference in schematic between Model A, B and X.

I tried a few permutations with D10 & D12 ( removing one/both) and that makes it power up at 145 MHz or even 50 MHz.

Can anyone help with this diode preset please?
73s Kris

24th Sep 2019, 9:09 am	#1
Kris_VK3XON Diode Join Date: Sep 2019 Location: Melbourne, Victoria, Australia Posts: 3	FT-780R model preset by diodes I've been restoring a Yaesu FT-780R and a bit stumped with the presetting of model A/B/X diode preset : I got a 780R with a weird mod, add on board that forces repeater shift to 1.6 MHz UK (I'm in Australia). Removed the board and repaired the cut tracks (2 x 4 bits), corrected the wiring back to MCU board for +/-/simplex. All good. So, now it turns out I have a Model B because the unit still starts up on 433 MHz.... but the stock repeater split is now 7.6 MHz (I need 5 MHz). According to the manual Model A is 435 MHz startup and 5 MHz split. (this is what I need). Looked in the user manual and the only difference I see in the schematic between Model A and B is that A has D10 & D12 whereas Model B has D12 only (my 780R indeed only had D12 soldered). So I added D10 which should turn it into Model A, however it becomes a Model X (starts up 445 MHz). I CANNOT find any other difference in schematic between Model A, B and X. I tried a few permutations with D10 & D12 ( removing one/both) and that makes it power up at 145 MHz or even 50 MHz. Can anyone help with this diode preset please? 73s Kris