Hitec Flash 4 SX Modification


How to turn your Flash 4 SX into a Flash 5 SX



Why this page ?
The Hitec Flash 4 SX and Flash 5 SX are both very good radios. The price difference between the two radios is only about $30. The problem is that if you own a Flash 4 SX radio, and one day you realize that you really need a Flash 5 SX, then suddenly you have to spend about $160.

This page explains to you how to turn your Flash 4 SX into a Flash 5 SX.


Here are the usual warnings:
  • Do these changes at your own risk. I am not responsible for anything bad that may happen.
  • By opening your radio, you will lose the warranty.
  • If you don't understand these instructions, put your Flash 4 SX for sale on eBay and go buy yourself a Flash 5 SX.

If you understand and agree with these warnings then let's get started !!!

As you may have already guessed, the Flash 4 and 5 are basically the same radio. One good indication is that they share the same user manual. What you will need to do is:
  • Check the size of the exisiting switch (trainer switch) and buy 3 switches of the same size (see below for the exact type)
  • Add the missing switches
  • Wire these switches to the Printed Circuit Boards (PCB)
  • Add a few resistors
  • Unsolder 2 resistors on the main PCB

The microprocessor used on the Flash 4 SX is the same as the one in the more advanced model, so there is no painful software upgrade procedure involved.

The switches
To simplify the instructions, we will assume that you want to add all the features of the Flash 5 SX (if that's not the case you may only add 1 or 2 switches instead of 3).

You need to get 3 switches with the following characteristics:

  • SW1: 3-position switch with 3 contacts. This is basically an inverter with an additional central position where the middle point is not connected to either contact. This switch is called a "SPDT (Single Pole Single Throw)switch with center off position"
  • SW2: this is the trainer switch that your Flash 4 SX already has. Nothing to buy.
  • SW3: 3-position switch (same as SW1)
  • SW4: 2-position switch. This is a SPST (Single Pole Single Throw) switch

The SW1, 2, 3 and 4 names are identical to the ones used in the user manual.

Let's get started:

  • Open your radio (8 black Phillips screws in the back)
  • Drill 3 holes for the new switches. You will see that the plastic box is already drilled (another indication that both radios are identical). Be very careful because the only thing you need to drill is a very thin aluminum plate. The most reliable way is to mark the center of the switch, remove the plate and drill it while it is held in place between 2 pieces of wood.
  • Move the trainer switch to the location immediately to the right (front view). This is where the trainer switch is located on the Flash 5 SX
  • Install the 3 other switches. Follow the user manual: they go SW1, SW2, SW3 and SW4 from left to right
The main board

There are 2 resistors that must be removed on the main PCB. One of them locks any action on channel 5 and the other one must be a pin that the processor reads to know if the additional features should be enabled or not. The resistors are 0 ohm resistors in  Surface Mount Technology (SMT). The label on top read "000". To unsolder the resistor, you must heat both side of the resistor with a soldering iron. There are different techniques to do that. The one I use is to go back and forth between both sides of the resistor with the soldering iron. Eventually, you can add some solder. This helps carry the heat.

  • Locate the 2 resistors to be removed (marked by the blue rectangle here below)
  • Unsolder them
  • Make sure that there is no residue of solder that may create shorts on the PCB

Wiring the switches
You must now wire the switches that you previously installed. On either side of the antenna, you will see 2 small PCB's. We will call them the left one and the right one. At the top of each PCB, you will see that there is a connector linking the 2 PCB's. This is illustrated here below (ignore the additional wiring that you don't have yet).

We will number the pins of the connectors 1, 2, 3... from left to right. The connector on the left has 5 pins and the connector on the right has 7 pins. What you must do is end up with the following wiring:

The connections between the Left and Right PCB are already handled by the connector linking the 2 boards. You just need to worry about the upper part that connects the switches. Use a small soldering iron and thin flexible electric wires. The schematic may appear complex but it is actually relatively simple: what you want to achieve is to have the center point of the switches connected either to pin 3 (Left) or pin 4 (Left) through a resistor and, for 3-way switches, left floating at a voltage exactly between 3 and 4. SW2 is represented but you should not have to change its wiring.

All the resistors are 4.7K and can be soldered directly on the switches as illustrated below:

Detail of the left side showing SW3 and SW4.


Detail of the right side showing SW1 and SW2.
Before closing your radio you must activate the new mode. This is the final step of the conversion. This is also the step that is the least clear to me. Please E-mail me if you have additional information.

The programming is done the same way the other programming is done except that there is a secret switch that activates it. If you look carefully at the main PCB, you will see that in addition to the 3 push buttons that are used to program your radio, there is 4th on, left of the 3 buttons. The following picture shows the placement of the 3 push buttons that appear on the front panel. In addition, you can see that there is a 4th one (secret switch) that cannot be accessed directly (unless the front plate is removed).

To activate the programming mode, short-circuit the 2 points marked by the red arrows and turn on the radio. You will get into menus that are similar to the ones used to program the other features of the radio. If you have additional information on the role of the different menus, please let me know. After a few trials, you will realize that your radio has now all the menus that are described in the Flash 5 SX manual. You are done !!!

Put the 8 screws back and enjoy...

Additional information
Feel free to link to this page. I recommend linking rather than copying so you will benefit from additional updates. If you link to this page, please E-mail me so I will inform you if I change its location (which I am planning to do soon).

If you have additional information that you would like to share (specially on the programming procedure), please E-mail me.

Updated on 07/02/2001

A special thanks to Herb for allowing me to reverse-engineer his radio; and to Karl of the Harbor Soaring Society for teaching me how to fly my glider.



My name is Bernard. I am French. I fly my gliders at the Fairview park in Costa Mesa, CA. I am a member of the HSS.


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