Yaesu FT7800/7900 LED Colour Change - G7SYW's amateur radio bits & bobs...

Yaesu FT7800/7900 LED Colour Change

| Posted in Misc stuff

This post described the method used to change the standard Yaesu FT7800/7900 amber display colour to white. Of course, any other colour, or mixture of colours may be used depending on personal preference.

Like any modifications, you carry them out at your own risk. If you don’t have access to a proper SMD soldering workstation and you’re using a normal soldering iron, use the finest tip (preferably pointed) that you have. Remember, these components are easily damaged by too much heat.

SMD LED size comparisonYou will require 14 x 0603 package (1.6mm x 0.8mm) SMD LEDs and 4 x 1206 package (3.2mm x 1.6mm) SMD LEDs. Please be aware that although this procedure isn’t too complicated, it does require some very careful soldering with components that are only 1.8mm x 0.8mm in size!
To give you an idea of their size, these are some of the original LEDs removed from the radio and microphone, placed on a penny coin.

Yaesu FT-7900 with original amber LEDsYaesu FT-7900 headMy decision to change the colour of the display was brought about after I purchased a 7900 to install in the car. The car has brilliant white LED instrument and switch illumination, thus the amber Yaesu FT-7900 looked a bit out of place. I also have an FT-7800 in the shack, I decided to change the LED’s in this radio first.

The reason for doing this radio first was twofold. Firstly, it was accessible – in fact it was in front of me. Secondly, I concluded that if for any reason the conversion didn’t turn out as planned, it was better to use the older radio as a guinea pig…

Both radio control heads are almost identical. The only minor differences are the size and shape of the knobs and buttons. Both control heads employ the same PCB.

Yaesu MH-48 Microphone LED replacement

As standard, the Yaesu MH-48 microphone, supplied with both these radios, has a dark red illuminated keypad. This colour doesn’t even match the head unit. Why Yaesu used different colour LEDs in the microphone is beyond me.

Before commencing, turn the radio on, enter the settings menu and select menu option 11 (Dimmer) set the dimmer to DIM1, this ensures the LEDs are in the lit state ready for testing later.

Remove the three screws from the back of the microphone, two near the cord, and the third on the mic hook. Carefully lift away the back shell with the “up” & “down” buttons, followed by the PTT lever. Remove the three screws securing the PCB and the single screw which holds the PTT switch. Some mics may also have a locating spring between the plastic upright and the PTT switch. If this spring is fitted, simply lift it off.Yaesu MH-48 Mic PCB removedCarefully unplug the cable from it’s connector and lift the PCB slightly. You will now need a small tool to gently ease the microphone element and it’s surrounding rubber insert from the moulding. Alternatively, unsolder the microphone wires from the PCB, noting where each wire is attached. Remove the PCB from the housing, .

With the PCB removed you will see five SMD LEDs. You only need to change four of these LEDs as the one in the top left corner is the TX light. Carefully remove the four LEDs.
Caution: do not use excessive heat for a prolonged period, or try to pull them off is not unsoldered as the PCB tracks are very thin and WILL lift away from the board and break!

Mic PCB with white LEDsAlong with all LEDs they are polarised and have markings on them to denote their positive (anode) and negative (cathode) end. Depending on the LEDs you are using, the marking may consist of a dot on one end, or an arrow printed on the back, for example. The LEDs required for the microphone are 0603 SMD package (approx. 1.6mm x 0.8mm)

When placing the new LED on the PCB, the two LEDs at the top have the cathode to the left, while for the bottom two LEDs, the cathode is to the right as viewed from the front.
If using solder paste and hot air, just hold the LED in position with a toothpick or similar to prevent it blowing out of position.
When using a conventional soldering iron, watch very carefully and apply the heat just long enough for the solder to melt. Again, you will probably have to gently hold the LED in position whilst heating the solder.

Yaesu MH-48 Mic with white LEDsPlug the mic cable into the PCB, and also into the radio. Turn the radio on and check all four LEDs are illuminated. Once everything is correct, re-assemble the microphone, taking note of the following: the microphone insert is placed in it’s housing and the plastic sliders for the switches on the side of the MH-48 are in place on the switches before the PCB is screwed in place as these cannot be done after securing the PCB.

Yaesu FT-7800/7900 Head Unit LED replacement

Yaesu FT7800/7900 head screwsRemove the rear cover of the head unit by removing the five screws. Turning the head over, pull the three knobs from the front of the panel, these may be quite tight, but the do just pull off. Behind the VFO knob is a nut, remove the nut and carefully withdraw the head PCB from the rear of the casing.

Yaesu FT-7800/7900 control head pcbYaesu FT-7800/7900 LCD securing tagsPlace a soft cloth on the work surface to prevent scratching the LCD and place the PCB with the LCD face down. Along the top edge of the PCB are three tags (circled in picture) very carefully bend them straight.

Yaesu FT-7800/7900 LCD removed from PCBTwo further tags can be found further down the PCB, these have a very slight bend in them which you also need to straighten.
Turn the PCB assembly over and lift away the LCD display unit. Note, along the top edge of the LCD unit are two plastic locating lugs which may be a tight fit in the PCB requiring gentle teasing away from the PCB. Be very careful not to bend the LCD as it is easy to crack the glass, the only repair for this is a call to Yaesu to obtain a new PCB assembly!

Also note, the LCD assembly contains a slab of clear plexiglass and a reflective insert, both of which may fall out if not carefully handled. Do NOT get fingerprints on or scratch the plexiglass block.

Yaesu FT-7800/7900 original LED'sBy studying this picture you can see a total of twelve LEDs are used on the head unit PCB. Ten of these LEDs are 0603 SMD package, while the remaining two are 1206 SMD packages. The 0603 packages are used for the two on the left, six along the bottom and two at the very right hand side. The two inner LEDs on the right hand side are 1206 packages.
The green dots in the picture indicate the cathode (negative) connection of the LEDs.

As with the microphone, the amber LEDs are removed from the PCB and replaced with the new LEDs.

The inner pair of LED’s on the right hand side are of a design with side-facing lenses, thus directing the light onto the rear of the LCD screen. At the time of writing (and carrying out the change) I didn’t have any of this type of SMD LED to hand. To overcome this, I mounted two 1206 package SMD LEDs on their side to achieve the same effect. The original LEDs had three solder pads, the center solder pad not being connected to anything.

Once all the LEDs have been changed, temporarily plug the head unit into the radio and switch it on by pressing the small switch on the upper right hand corner of the PCB. If all is well, all the LEDs should light.

If everything is working correctly, refit the LCD assembly securing it by bending the tabs on the rear. Be careful not to bend the tabs too much and disturb or short-circuit any of the components on the rear of the PCB. Re-assembly of the rest of the head is a reverse of removal.

Yaesu FT-7800/7900 LCD refitted
Yaesu FT-7800/7900 with white LEDs
Yaesu FT-7900 fitted in car

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