normsweb.com - mods and repairs for Yaesu FT 757

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		Yaesu FT 757 mods and fixes

			NOTE:- The Info on this page has been gathered from different sources around the net. I have not tested all of these mods, use them at your own risk.



		Frequency expansion:

			This gives 1.5khz - 30mhz full coverage Disconnect the radio from all connections. Remove top cover. Locate SW03 (behind and slightly to the right of the tuning knob) Flip the switch, and put radio back together.



		Radio appears dead (meter lights only):

			While in receiving position, the figures and symbols on display became gradually dimmer, and then suddenly the display went off and reception stopped. No transmission nor reception was possible. Just the two pilot lights of the meter remained on. The Soloution: The DISPLAY UNIT (front panel) 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 replacing it with a cheap BD135 makes the rig feel happy and it worked right off the bat Important Note: I have been advised, by Rick Jackson from Euro Radio Co, "Do not replace Q01 (2SC496Y) with BD135 as it will cause problems with DC/DC converter due to heat" Take heed folks, Rick knows what he is talking about.



		FT-757 AM Filter modification:

			The original AM filter is too wide for shortwave listening (6 kHz). There is a very simple way to decrease the bandwidth on AM mode to about 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. FT-757 (not mark II) Filter modification During RTTY/AMTOR operation it is useful 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. 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. 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. Connect the OFF contact to pin 5 of J10 (SSB 8V) and ON contact to pin 8 of J10 (TX 8V). 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. Connect the switching (middle) contact of second pole to pin 7 of J10 (RX 8V). The OFF contact will be let free.



		FT-757 Mark II Filter modification:

			During RTTY/AMTOR/PACTOR operation it is useful 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. Cut the connection between cathode of diode D 101 and D102 on RF UNIT. 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. Connect the OFF contact to anode of D102 and ON contact to collector of Q56 (TX 8V). 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. Connect the switching (middle) contact of second pole to collector of Q57 (RX 8V). The OFF contact will be let free.

Connect a PK232 to a FT-757:

Output Connections of PK232:

PK232 connector	PK232 cable	Yaesu FT-757 radio
1 = RX Audio	Green wire	AF output BNC behind the FT757
2 = TX Audio	White wire	AFSK input BNC behind the FT757
3 = --	Black wire	Not connected
4 = Ground	Brown wire	Ground of one of the BNC
5 = PTT	Red wire	PTT input BNC behind the FT757

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

You must not have loop in your ground circuit. Use only a single ground link between the PK232 and the FT757



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