Modifications for the Yaesu FT-757
FT-757 AM Filtermodification


The orginal AM filter is too wide for shortwave listening (6 kHz).
There is a very simple way to decrease the bandwidth on AM mode to abt 3,5 kHz. Just cut the wire (bridge) in front of JP 1020 (left of CF01, looking from front side of transceiver) on RF UNIT board. Now take a new 1N914 (or similar) diode and solder it's anode to cathode of D61 and the cathode of this new diode to cathode of D58 or D59. Now the smaller SSB filter on 455 khz IF side is selected during AM. The function of WIDTH system is also improved on AM now (sideband selection is possible in AM with WIDTH knob). SHIFT is out of function as before modification.

This modification does NOT work on FT757 Mod II, because there is no second SSB filter.

You can find a CW filtermodification for RTTY/AMTOR in an other file.

I will send circuit diagramms of further modifications on request. Write to : Roland Robic (OE6RCD), Augasse 15, A-8430 Leibnitz, Austria. Please enclose 3 IRC's in Europe or 5 IRC's outside Europe (airmail) to cover postage.

vy 73's de Roland OE6RCD @ OE3XBS.AUTEU

FT-757 Mod II Filtermodification


During RTTY/AMTOR/PACTOR operation it is usefull to have an narrow filter to reduce QRM from other stations. It is possible to use the narrow CW filter of the FT 757 II for SSB, because of the filter shift system.
  1. Cut the connection between cathode of diode D 101 and D102 on RF UNIT.

  2. Take a new diode (1N914 or similar) and solder it's cathode to the the cathode of D101. Connect the anode to middle contact of a double pole toggle switch.

  3. Connect the OFF contact to anode of D102 and ON contact to collector of Q56 (TX 8V).

  4. Take another diode of the same type and solder it's cathode to pin 1 of J09 and the anode to ON contact of the second pole of toggle switch.

  5. Connect the switching (middle) contact of second pole to collector of Q57 (RX 8V). The OFF contact will be let free.

For the SPDT switch I am using the MOX switch on the front panel.
It is a 2 pole toggle switch and you have to cut the PCB between the contacts. Further you have to remove all wires from the MOX switch.
That's all.

If you want th have a complete modification diagramm together with some other modifications, write to Roland Robic OE6RCD, Augasse 15, A-8430 Leibnitz, Austria.

Please enclose 3 IRC (Europe) or 5 IRC (outside Europe Airmail) for covering postage.

Best 73's de Roland OE6RCD @ OE3XBS.AUT.EU

FT-757 Filtermodification


During RTTY/AMTOR operation it is usefull to have an narrow filter to reduce QRM from other stations. It is possible to use the narrow CW filter of the FT 757 for SSB, because of the shift/width system.
  1. Cut the connection between cathode of diode D 102 and a 150 OHM resistor on RF UNIT. This resistor is not shown in service manual,but it exists on all rigs later LOT 4.

  2. Take a new diode (1N914 or similar) and solder the cathode to the open end of the 150 Ohm resistor. Connect the anode to middle contact of a double pole toggle switch.

  3. Connect the OFF contact to pin 5 of J10 (SSB 8V) and ON contact to pin 8 of J10 (TX 8V).

  4. Take another Diode of the same type and solder it's cathode to pin 1 of J09 and the anode to ON contact of the second pole of toggle switch.

  5. Connect the switching (middle) contact of second pole to pin 7 of J10 (RX 8V). The OFF contact will be let free.

For the SPDT switch I am using the MOX switch on the front panel. It is a 2 pole toggle switch and you habe to cut the PCB between the contacts. Further you have to remove all wires from the MOX switch.
That's all.

Attention : There are some errors in the Service Manual. F.e the filter connection is shown wrong. If you want to have a corrected circuit diagramm and complete modification diagramm together with some other modifications, write to Roland Robic OE6RCD, Augasse 15, A-8430 Leibnitz, Austria.

Please enclose 3 IRC (Europe) or 5 IRC (outside Europe Airmail) for covering postage.

The Display became dimmer more and more


Hello FT-757GX users!:
This bulletin intends only to provide help if you ever happen to have in your FT-757GX the same trouble I have just had.

THE TROUBLE:
While in receiving position, the figures and symbols on display became dimmer more and more, and then suddenly the display went off and reception stopped at once. No transmission nor reception was possible. Just the two pilot lights of the meter remained on.

THE SOLUTION:
The DISPLAY UNIT (front pannel) has one transistor marked Q01 (or Q4001) 2SC496Y which is a NPN Silicon and its application is as oscillator for the DC to DC converter.
This transistor controls the TO1 (DC to DC converter) which, among other things, generates the -8 volts required in several sections of the circuitry, the RF UNIT in particular is highly affected and the receiver does not work if this voltage is not supplied from the DISPLAY UNIT.
Removing the transistor in bad conditions, and replaced by a cheap BD135 makes the rig feel happy and it worked right off the bat.
Special care is to be observed while removing the DISPLAY UNIT PC board. There are three screws to bbe carefully removed to avoid washers falling into the jungle of wires and small parts. There are some 12 press buttons in the front pannel through which you apply preasure to their small switches on the PC board. Two of them are a little bit difficult to remove, the UP and DWN (band/channel) buttons have squared holes where the shafts for these controls are placed before they reach the PC board. Pulling gently and firmly the PC board backwards (to the rear) with the help of a screwdriver makes easier to free it.

Hope all this is of help to anyone needing to make repairs in this rig. If you are not sure that you can make it for yourself ask your Elmer!

FT-757GX and GXII - TX 1,5 to 30 MHz


  1. Disconnect FT757 from all connections.


  2. Open tranceiver like explained in your "OPERATING MANUAL".


  3. Locate on the "CONTROL UNIT" SW03 and change is position.


  4. Close tranceiver back and reconnect power.


  5. This give you 100w between 1,5 and 30 mhz.

There is also a temporary solution, without use of tools:

While the PTT-key on the microphone is pressed, -push one of the up/down-keys at the frontpanel. Now your 757GX transmit on the desired frequency, - but just for one transmission (until you depress the PTT-key).
Connect an PK232 to a FT-757


Output CNX of PK232 :

PK232 connectorPK232 cableYaesu FT-757 radio
RX Audio = 1= GRN wire= to AF output BNC behind the FT757
TX Audio = 2= White wire= to AFSK input BNC behind the FT757
--= 3= Black wire= Not connected
Ground = 4= BRN wire= Ground of one of the BNC
PTT = 5= red wire= to PTT input BNC behind the FT757

The BRN wire and the shield of the PK232 cable are connected together.

You can use a alone cable for the reception of the PK232 wich is connected to the AF output of the FT757 instead of the RX audio (green wire).

To avoid larsen, you have to not have loop in your ground circuit : So, use only a alone ground link between the PK232 and the FT757.


Yaesu FT-757GX

Remove the top cover,locate the small black switch that is located on the edge of the big horizontal board near the back of the main tuning dial, it will be under a bundle of wires.

Flip the switch, and put radio back together.

This allows general coverage.


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