FT-757 (GX or GXII) page (service notes) (Dec 12-2019)
there are plenty of tips for Anyone who is still working with and on FT757 type radios. Thanks to the ham in Ontario who submitted this information.
Above pictured the FT757GX that had problems. As can be seen on the display.. the rig (at the time of the photo) was on the “P”Priority frequency. I did not select this PRIORITY frequency…the rig did this on its own. The logic circuitry was acting up. I did not feel confident working with the dense circuit layout of the FT757GX. I then traded this problematic 757gx to another ham in Ontario. He traded me back an older radio – a Swan 100MMX. The Swan is an early solid state transceiver and the circuitry is much simpler– IF I ever have to service the Swan– I feel confident doing so.
This ham in Southern Ontario did pass me some very useful information and Service NOTES. Here below they are written out for those hams who still service radios.
Some folks call this the ‘GX I, but there is no official model 1 of any thing.
general coverage too. The TX Finals are near bullet proof. Metering is done by a real meter also. The downside is that it is quite compact and is a challenge to fix in some ways. There are no parts to speak of and while many are being parted out on eBay these parts too are 30 years old. Overall this isn’t too bad,
but parts that wear like shaft encoder are unavailable and any from a parted out radio are likely to be worn also. In the author’s opinion, the biggest problem with this radio is the “Local Unit” otherwise known as the synthesizer. Its noisy and therefore reduces the receiver performance some. It does not render the radio useless;its just that the FT-757GX is readily beaten by more modern HF radio examples.No one makes a radio that looks like this any more. Modern radios are all SMD these days and not easily serviced at home. Neither is this radio
cost effective to send out for repair. Its not worth much and any real repair that requires a board to be pulled to replace a part will exceed
in labor at $70/hr what the radio is worth. For the few hams left that are capable this radio can be serviced at home.
Its still a good performer for general use and to those Radio Amateurs that regard this as a hobby, its a good radio for mobile, cottage or
portable. In other words, a perfect General Use radio. A Used FT-757GX
The problem with 30 year old HF radios is that they can have 25 years of neglect. The first 5 years of a radios life is where it is respected and
has resale or trade in value. After that it appears to the market as a “back up radio” and after that it starts to acquire the status of “beater”.
People stop to care anymore. The FT-757GX is a perfect CB radio. It can be made to go on 27 MHz with radio attractive at the Dealer in 1983 apply to the CB crowd in Year 2000. The CB crowd has little to no radio knowledge other than mutual support and that is often driven by rumor, myth and innuendo. Radios get modified for more “swing”, punch, modj or horror – RF output (a modified FT757 will “swing” 150 watts). These folks have little skills to do repair and will
crack a radio covers at the drop of a hat and proceed to modify a radio with nothing more than vice grips and a 300 watt Black Beauty iron.NO wonder 27 MHz sounds so horrible. Simply put – if you are looking for an FT757 be very careful of where it can come from.
The FT757 has a row of adjustment pots along the rear panel. The knobs are often missing and the knobs are unobtainium.
The original model did not have that many factory changes although there are a few. In particular Yaesu improved the CW QSK that was incorporated
by Series 5 and some Series 4. The most common fault with these radios is the failure of the front end PIN diodes. Usually they will be found shorted. Failure of these diodes (depending on which ones, of course) often is illustrated by the FM RX being dead or the Squelch control acting “funny”.
The S Meter is lit by 2 wired in bulbs. The illumination is inadequate even on a new radio. Today all of them have burnt out at least once and
what they get replaced with can be very inventive. No bulbs are available from Yaesu. Their orientation is critical for proper illumination. But
bulbs – reasonable replacements – ARE available.The top cover is the Final heat sink. It is large, heavy and has a thermo
controlled blower. It also has gaps that allow small items to enter. Thats often where I find the missing screws. This is a 30 year old radio and around now the electrolytics are starting to dry out. Unlike the TS-50 these capacitors are not leaking out, they’re just drying out. Relatively speaking they are easy to replace and notworth troubleshooting beyond the first one that goes. Modern capacitors are smaller and have a lower ESR. Once the board is out, may as well have
at as many as you can.
The FT757 has a memory back up battery. Chances are its near dead if it original or possibly replaced by some interesting methods involving a small
soldering iron. I’ve also seen original memory batteries still soldiering on and providing back up sitting at 2.65 volts. The above is not in any way to represent Service Notes, but rather is a short list of what are the nuances of a used FT757GX.
The FT-757GX II
Obviously this radio followed the original model. It looks quite similar and is exactly the same size. It shares all of the above cautions and features of the original model, including part numbers. Its main difference is the ‘II does not have Shift/Width. Instead, this model has IF Shift and IF Notch. The latter is completely manual.
Aside from that, I think one of the major changes with the second model was the improved computer control. Its still crude and don’t forget that
“Computer Control” meant DOS and at best a 286. This radio was 10 years before any version of Windows. In the authors opinion the original version with IF Shift/Width is much more useful. To each their own.
Issues and Repair
Certain traits and faults are unique to the FT757. Specifically this radio used steering diodes to switch signals, audio and the front end BPF. It is these diodes and specifically the BPF where a lot of strange operation from diode failure can take place. The diodes in the BPF are severely under rated and prone to failure in a
strong signal environment such as Field Day. Their failure is often as a short, and its this that leads to some interesting failure modes in the radio itself. The good news is that a common 1N4148 is a good replacement. These are NOT PIN diodes, but they serve well and provide adequate isolation and low loss. This is after all HF. The bad news is I’ve seen Yaesu use Schottky diodes in some production runs and you should not mix them. 1N4148 have a forward voltage drop of about .65V and the Schottky diodes are around .27 V. A simple VOM reading will tell you which is used. In the case of the Schottky diode, use 1N5711. Now it
could be that I have encountered a radio thats been badly repaired, but I doubt it.
This only seems to be in the radio’s front end. Similar diodes are used in many other places in the radio but their failure rate is much less. The specifics of the above will be addressed in further detail.
Specific FT757GX Failures
1) Service manual errors.
4) No FM; FM permanently squelched.
6) Memory battery
7) Low RF output on some bands
8) Poor or no receive on some bands
9) PLL alignment
10) Pre Amplifier Gain
12) CPU Reset
13) Reverse Voltage
14) Display Problems
15) Meter Lighting
16) Power On Problems
17) Pulling the Circuit Boards
18) Final Amplifier and the “MARS Mod”
1) Service Manual Errors
Setting the CW BFO offset crystal. The manual wants you to set the CW trimmer TC2004 to 8.215.900. Ignore this adjustment. TC2004 is for
LSB. The actual CW adjustment is covered under Point I in the Service Manual.
This is quite common in many old radios. In the case of the FT757 it is often caused by oxidized pin headers. This is especially evident if
the display sometimes goes weird on you. The fix is simple and this should be a common practice for every flea market and eBay refugee.
CLEAN THE RADIO
You need to do this as soon as the radio is in your hot little hands. You need to pull out every pin header, hit it with some deOxit and
reseat. EVERY pin header. It will take you an afternoon. There are a lot of screws to undo – especially to get to the PA deck. Pull the knobs and get them into some warm water and dish detergent. Windex, or better…. Invisible Glass. I once had an FT757 that must have been in a barn with a heavy cigarette
smoker. This thing stank and was covered in brown dusty goo. The dial skirt had smears of yellowy brown guck. The heat sink channels were filled with a thick layer of brown gunk. There was only one thing I knew of that would touch this…. CLR. I spent hours on it. I powered it up the moment I took it out of the delivery box and knew immediately what I was in for when the display read 27.165.0. It was advertised on eBay as “works well but the display is intermittent”. I needed rubber gloves to tune it.
The display problem was fixed with deOxit.
CLEAN THE RADIO
Improper disassembly can ruin the radio. The top cover is heavy and held in place with just 4 – 3mm screws. Attached to this top cover are many small wires and a few coax cable runs. The bottom cover screw removal is straight forward, but the bottom cover itself will not come off without some GENTLE expansion.
The top cover will allow itself to be flipped over the back, but there are a few wires and cables that are attached. They are completely unforgiving if the top cover ever gets away on you. There is a large cable harness tucked into the rear chassis joined to the top cover, plus a number of wires connected to the back of the front panel. If you have the bottom cover removed, the top cover will flip out on to a large book about 1/2″ thick nicely. From this point on you need to move the top cover and the rest of the radio as one unit.
The front panel is on a short rail. It is held in place by 2 screws on either side of the main chassis. Once loosened and NOT removed, the
front panel may be slid forward about 3/4″. Don’t forget to undo the ring around the Key Jack. If its missing, some one has been dancing
on the RF Deck.
When you go to put the radio back together note the large exposed harness at the back of the radio coming out of the PA Deck. You will not be able
to get the top cover back on unless this harness is tucked away properly. If the top cover will not settle such that you can screw it down without
force, then you need to have a look and see whats going on and why. A SPECIAL NOTE ON THE COAX CABLES
NEVER remove a chassis mounted coax cable by pulling on the cable. EVER. The coax cable is just press fitted into the little connector at the end.
Remove the cable from its socket by pulling on the “ears” that are actually part of initial assembly crimp. Once you rip the connector off,
you’ll never get it back on.
There is an aluminum cover over the PA unit. Note that there are THREE countersunk 3 mm screws. Two are in the center near the front and one is
at the back in the corner right on the edge. If the top cover will not seat properly when you go to put the radio back together, you have a
normal screw where there should be the counter sunk screw, most likely.
4) No FM RX
This is VERY common to this model radio and usually is indicative of other faults too such as poor receive on some bands. Measure Pin 5
on the MC3357 on the IF board while in receive. It should be near zero. Chances are its high. DO NOT adjust the squelch level pots.
You will likely be drawn to believe that Q68 the TX 8V switch is leaky. Chances are its fine. The fault is a shorted PIN diode in the BPF. There
are a number that it could be, but do not despair. The fix will take some time but it will not be expensive.
Proceed to Point 8) for PIN diode detail. The squelch circuit for FM does not use the same method for the IC that manufacturer documents. There is an adjustment for the squelch control, and there is also a master trim pot for recovered audio. The radio has an all mode squelch thats AGC controlled, more or less. The same for the scanning function it too is driven from the AGC.
Its usually caused by the 15 MHz master oscillator. Part of the fix for this involves changing the PLL crystals. Yaesu has no stock on
these items. You are reduced to changing the trimmers for ceramic models. Mouser is your best choice and sometimes Dan’s. You want the
2 pin 7 mm variety. Yaesu no longer has the trimmers available. There have been reports of these radios drifting, but I have yet to
experience it despite a number of FT-757GX that I have had.
6) Memory Battery
The radio is very inconvenient to use without a memory back up. Upon powering up it will default to 7.000.0 MHz if the battery has gone South.
There is a trick repair on the Web that allows for its replacement without pulling the Local Unit. On the other hand while the original
memory battery is available and expensive, there is a common Lithium battery that you can use in its place if you are not afraid of doing
a proper repair and pulling the Local Unit.
A near drop in replacement is a CR1220 Lithium battery. It comes with solder tabs. Its possible, at least in theory, to snap the tabs off the
existing dead battery and solder the new battery to the stubs. Chances are you’ll melt the solder on the circuit board but it might be worth a
7) Low RF Out On Some Bands
This is similar to 8) that follows but the symptoms are that the receive is OK but the TX output is down either on a band basis or every where.
Once again, depending on what diodes are done the FM mode on RX could be permanently squelched.
More or less, if a particular band is good on RX, it should be good on TX. That is the BPF is common on both RX and TX. This is the circuit
block that has all the coils and is diode switched. The diodes switch the appropriate BPF, but additional diodes steer or connect the selected
BPF between RX and TX. Before attempting to fix low or no TX on a particular band you should determine the health of the RX. Fix the RX first. If you determine that the RX is fine, then your potential diode switching problem is limited and much easier to find. Part of evaluating the RX is seeing if the RX is squelched on FM.
Does the preamp work? If the RX is squelched on FM, quite likely one or more diodes in the BPF and area are bad…. usually in a shorted condition.
If a particular band is dead on RX and TX then there is a good chance that the BPF selector diode(s) are gone plus the BPF input coil. Not only does
the coil tune, it is also a DC path for the select diodes such as D07 and
D08. In this case L04 and L08. You can use an ohm meter to test the coils. In most cases the diode
will show a short. That is instantly a bad diode but it can also be in an open state. The diodes in question are 1SS83 for the BPF rated for
300 Vrev and 1SS53 elsewhere rated for 25 Vrev. Don’t let these ratings fool you. Either diode has been found in a failed state in this radio.
8) Poor Or No Receive
In situations where the receiver is just simply dead, check the lamp fuse on the RF Board. It can be replaced by just about any bulb of the same
size. Its not critical. Either you were in a strong RF environment, or you used the transceiver for a dummy load or perhaps the bulb just died
from old age – who knows why it opened. Unconfirmed specs on the bulb are 8V at 100 mA.
But before you put the covers back on, check the radio out. It could be that whatever took the bulb out could have also cleaned out some of the
front end PIN diodes. Also check that you have FM RX and it squelches properly.
If you find a band thats dead, but its diodes are good then you need to ohm out the BPF coils, for they are the ones that complete the diode
conduction path. For instance for the 40M Band diodes D11 and D12 switch the BPF array for 40M. Coils L14 and L15 not only are tuned to 7 MHz,
but they are the conducting path for the diodes.
Diodes D112 and D113 protect the RX during transmit. If the bulb is open, these diodes are immediately suspect. Diodes D03, D04 and D06 form signal routing to and from the diode switched BPF. If the bulb is open, D03 and D04 could be bad. Consequential damage could have D06 compromised and therefore have weak RX and TX exhibited.
I have never seen D01 fail, but if it has you’ll need to replace it to find out if Q01 and Q02 have been taken out.
Some of these diodes, in particular D112 and D113 may be located on the bottom of the board. You’ll need to pull the board to get access. You
may see a blank component at the marked location on the circuit board. If you need to pull the board, you may as well make the pre amp mod.
Before you start replacing PIN diodes you’ll need to see if they are just silicon diodes or Schottky. If you encounter the latter you need
to use 1N5711 for PIN replacement diodes. Mixing them up may turn out bad as the usual silicon diodes have a higher voltage drop and may stop
the others from conducting.
9) PLL Alignment
Is more or less straight forward from the Service manual. If there is a crystal that won’t align, replace its trimmer with a 7mm ceramic. It DID
adjust at one time, so its either the crystal or the trimmer, most likely. May as well blame the trimmer as replacement crystals are not to be had
any way. The 15 MHz crystal frequency adjustment is critical for the display to be accurate.
The IF Shift and Width controls must be centered. That is the lines on the knobs must be pointing straight up, and this is only possible if the knobs
are positioned properly on the control shafts.
10) Pre Amplifier Gain
The pre amplifier has far too much gain to be useful. I question its value to begin with since all it appears to do is just increase the back
ground noise. This is not the fault of the amplifier but rather is a fault of the synthesizer.
You can reduce the gain of the pre amplifier and improve its AGC action by removing R22 and installing a 1N4148 in its place. Cathode to ground
The attenuator has a 20 dB loss, which in use to me is excessive. Change R04 to 220 ohms for a 10 dB loss or 360 ohms for about 15 dB. 360 ohms is
not common but is a common value in 5% tolerance. Feel free to use a 330 or 390 instead.
The board in question is the TX LPF Board.
12) CPU Reset
Sometimes after repair the CPU will lock up. Sometimes you might want to clear memories.
Turn the radio off. Push in both black square buttons on the rear panel
(linear and Marker). Turn the radio on. Turn the radio off. Reset both
buttons to their out position.
This DOES NOT APPLY to the FT757GX II.
13) Reverse Voltage
Many Yaesu HF radios of this vintage have a master relay thats engaged when power is applied. The power on relay is on the RF deck and has a
steering diode in series with the relay coil. The radio simply will not power up with reverse voltage applied.
No damage to this radio with reverse voltage.
14) Display Problems
The radio uses a custom display electro luminescent vacuum tube. I have found the tube itself to be robust and encountering one that is dim by
it being at fault is rare. More often tan not its a fault of the voltage inverter and that is usually a fault of the inverter or the filter caps
for the negative supply. The radio does have a negative 8V supply line driven by the display
inverter. Failure to have this -8V line is the responsibility of many operational problems but is most likely observed in a weak display. The
inverter is unlikely intermittant, Dealing with the display and the inverter is a bitch as it involves mucking with the front panel.
A lot of display problems are resolved simply by cleaning the radio. I have had intermittent displays. In this case it was caused by the
solder failing on a pin header socket on the synthesizer. The wiring at the front of the synthesizer board can get compressed by the top cover
and over time the pressure fatigues the solder joint,
15) Meter Lighting
Illumination of the front panel meter is poor. Its always been poor. It was poor when the radio was new. Now, 35 years later it probably isn’t
any better, if not worse.
The radio originally had these bulbs in little blue booties that were press fit into the clear plastic ears on either side of the meter. As
the years have gone by there have been many inventive ways of mounting new bulbs. I have tried clear LEDs and the success is at best moderate.
It seems that there is no substitute for a real light bulb in this application. Yaesu no longer stocks these bulbs.
Grain of Wheat bulbs will not fit properly. One needs to be careful to use a low wattage bulb as the heat from the bulb will do damage to the plastic mounting
recepticle. A 12V bulb at 40 mA looks to be ideal and a good place to start is a 2174 from Bulb Town. Its a T1 3/4 size bulb – 5.5 mm dia
by 8.6 mm long. Something like .22″ by .35″.
16) Power On Problems
The radio will not power on with the MOX button pushed in. There is no indication that anything is amiss, and you are lead to believe that the
power on relay or its swiching logic has failed. The master power on switch is not directly involved with
10A relay and some TTL logic. The switching transistor is a Darlington. The whole thing is steered through a silicon diode that prevents the
relay from closing with reverse voltage. Both the MOX switch and reverse power appear the same – the radio will
not power up. If it won’t power up, it can’t be damaged. This may not be the case in a mobile installation as likely the radio is grounded
to the chassis.
Some mobile installations can fail in a spectacular fashion depending on how the power is routed. A few scenarios can be prevented by NOT connecting the DC cable negative to the negative battery terminal.
A properly working FT-757GX will cycle the fan upon power up. The fan will spin for maybe 1/2 second and then stop. Likely you will only be
aware of this with the radio opened up for service. The 4 pin power connector uses all the pins. There is the usual 2 pins
allocated for 13 VDC power, but the 2 other pins, when shorted, allow the final amplifier to function. This power connector was used in other Yaesu
of this vintage such as FT-107, FT-747 and FT-707. Its known as a Cinch Jones S-304.
18) Pulling the Circuit Boards
The first time I had to do this I thought that I’d never get it back together in a working state. It was a sinple problem – the AGC capacitor
had opened up. All AGC was FAST. I found out that it really wasn’t THAT bad to do. Since then I have had the Local Unit out so many times and back in that
I can almost do it blind folded. Its on this board that the memory back up battery resides. I have seen the youtube on how to deal with this
without pulling the Local Unit, as if having to do this was something to dread. Today, I’d pull that board without hesitation and have a new
battery in there quickly
. No mercy. Pull the board. Replace the battery with a CR1220. Do a proper job.
To get at any of the 757 boards you need to at least pull the bottom cover. That means 8 – 3mm appearance screws, 2 screws for the side feet
and 2 screws for the handle. When I pull a radio apart I have multiple bins for the hardware. This would all go into its own bin and I’d start a
new bin for the next “layer” of dismantling. I use old pill bottles.If you just want access to the RF Unit you only need to undo the two
screws at the top cover/ heat sink. Once you do that, you need to be very careful in handling the radio and heat sink. They need to move
To access the RF Unit and Local Unit you need to loosen the 2 screw on either side of the front panel such that you can slide the front panel
out about 3/4″. This will give you room to extract the RF Unit Circuit Board. Before you undo any of the circuit board screws you need to gently
pull all the pin headers and the coax cables. Note the previous caution on dealing with the coax cables.
To gain access to the Local Unit circuit board you need to unscrew all of the above, plus loosen the top cover/ heat sink and fold it back. Next,
remove the shield and then uncouple all pin headers and coax connectors. Remove the 3 pin header from the voltage regulator bolted on the side.
Near that IC on the circuit board are 2 – 5 pin headers. Mark one of them so they don’t get swapped. Note that some wires were above the
shield. Remove the 4 small knobs at the back and undo the ring around the KEY jack. Slide the board out by moving it back towards the front
panel and over the side with the regulator. You may need to push in the two switches to get clearance from the rear panel.
To gain access to the PA unit and the LPF you need to do all the preceeding, fold the top cover back and undo all the screws holding the
shield in place. Its obvious how it is removed, but be VERY carefil of all the wires and coax cables surfacing out from the cut outs. Note
which screws came from where – they are not all the same. The front panel is removed by removing the 2 screws on each side of the
chassis and removing all the cable headers. The main tuning knob is a slip on – it just pulls off. Behind the main tuning knob is the knob
The keyer sub board on the top cover is just screwed in. Be careful not to loose the 3 slide knobs.
18) Final Amplifier and the “MARS Mod”
The PA transistors are 2SC2290 and are capable of more output than the radio’s rated 100 watts. Actually, through miss adjustment the radio is
capable of almost 150 watts. That doesn’t mean you should do this. That does not mean the transmitter will be clean at this power and it also
means that you have lost any cushion against a mis matched antenna. The radio is also dead simple to do the “MARS Mod”. Its just a simple
matter of throwing a switch. It completely baffles me why you would want to do this. EVERY FT-757 I’ve encountered has had the switch thrown for
One of them came to me in the mail and when I fired it up for the first time the display read 27.165.0. Uh huh. It also looked
like it came from an Opium Den and smelled like it too. Its a 100 watt radio. Keep it that way. Its also a Ham Band transceiver.
Thats where the transmit should be used. Only there. Get it?
Oh yes. I have a few of these radios. All of them now have the open transmit disabled. I cannot think of any reason why a Ham would open up
the transmit on a transceiver other than “Angst Against the Machine”.There is a control on the back of the radio without a knob. Its the “AM
Carrier” control and usually you will find it fully clockwise. Like many SSB transceivers the FT-757 does AM TX by injecting a carrier on top of
a normal SSB transmit. From the Balanced Modulator to the SO239 the radio is a linear amplifier for low level generated AM. The absolute maximum
carrier the radio can support is 40 watts and still stay linear. I set this control to 25 watts carrier.
18) Shaft Encoder and Parts Availability
A good assumption with an FT-757GX is that there are no factory parts. Thats not literally true in some cases like the power on relay or the
meter light blue booties, but the real meat and potatoes parts like the shaft encoder and Local Unit crystals are long gone.
The good news is that yaesu Service Manuals are on line, and in some cases a newer model uses much the same parts and they ARE available.
I have yet to test it, but my gut feeling is that a shaft encoder from an FT-840 or FT-890 might work just fine for instance. I haven’t
tested this (yet).
In quite a few cases a later radio uses the same part under a different part number.
And last – there is always a junker around from which to raid. In the case of the FT-757GX the production run was quite stable. The shield
over the Local Unit changed over time but that is nothing compared to the sea of board changes the FT-107 went through. You are pretty safe
buying a “working pull” from just about any FT-757GX. In extreme cases you might loose or get a factory QSK mod, but thats about it.
This has been my experience with this vintage Yaesu. The radio STILL does a good job on HF even 35 years after its release. Perhaps its not
a Killer – if even it was 35 years ago, but its still perfectly usable. I won’t defend it by saying “there are worse”. Thats not saying very
much – is it?
The attraction to me is that these radios are “easy” to service. There is some SMD in there, but you have to look for it. Its 99% through hole
assembly. Its built like a tank and the finals, if run at 100 watts are bullet proof. It has a real S Meter and there are NO accessories to buy.
It came out of the box in 1984 ready to Rock’n Roll as is. Yes, a modern radio – say some thing as lowly as an IC-718 will run with it as an equal
if not “better”, but between the two the 757 has much more charisma and charm. Plus…. I can fix it and align it.
This radio will never be sought after or remembered fondly like a TS-830 or an FT-902DM. It will forever be looked upon as “an old HF transceiver”.
You can get a good hint of this by the number of them being cut up and having the pieces sold on eBay. There is no shortage. This is indicative
of both lack of parts, general failure with age and it being not cost effective to send out for repair. It also suggests the overall lack of
skills to fix these radios and possibly the desire to do so in the first place.
While we may be in a minority there are still folks out there in “radio land” that really are not that attracted to modern radios despite their
obvious functional superiority. A Yaesu FT-450 will blow the doors off an FT-757.
But its not the same.