A replacement display for the ft290r mk I

Introduction

I am the proud owner of an FT290R which I bought in the 80’s when I was first licenced as a G6. I think it’s an excellent radio, so I bought another one to have in an alternative location. It had a display fault, but I am an electronics engineer by trade so I figured it couldn’t be that hard to fix.

As usual I was wrong, there were a number of stumbling blocks as follows:

  1. The display itself cannot be sourced as a direct replacement
  2. There was little information I could find about the driver IC

So, the above two points ruled out simple replacement of the parts.

I searched further and found references to two very good sources of information

ZS1KE’s reverse engineering design and Dave Crump G8GKQD article in Radcom, December 2016

Both of these were very informative about how the display is updated but obtaining the displays was challenging so I descried to do my own redesign based on cheap Arduino and OLED display.

Design

The display is constantly updated from the FT290R microprocessor, and the display data is delivered over a 4-bit bus in something similar to ASCII.

My biggest challenge was that I wasn’t sure that the simple Arduino could keep up with the refresh rate of the display updates. It turned out that it wasn’t a problem at all.

I also wanted a cheap and flexible design so that elements of customisation would be possible, and the Arduino seemed ideal for that.

Circuit

The display is constantly updated from the FT290R microprocessor, and the display data is delivered over a 4-bit bus in something similar to ASCII.

The connections to the OLED module are very standard and utilise the I2C protocol. At the time of writing these are available from Amazon at £4.99 for three.

The Arduino’s I used were 16MHz ATmega328P Micro Controller, Nano V3 also pretty inexpensive at £10.99 from Amazon or much less from Aliexpress.

Get the ones with unsoldered headers, you won’t need the pins for this project, in fact it wouldn’t fit in small space in the FT290R.

As you can see from the circuit, I added a white LED to replace the incandescent lamp that is also a known failure on the FT290R and a real pain to replace. More about how to install that later, but I decided that I might as well have it under control from the Arduino, the software currently turns it on shortly after startup, but you could modify this as you see fit.

FT290R Disassembly

I followed G0GRE’s useful disassembly guide.

Clearly in this case we are not only replacing the bulb (as we completely changing the display the bulb is on the display board so needs to be replaced) the disassembly instructions are handy nevertheless.

Display Board

For this modification I found it easier to do away with the original display PCB and LCD see below:

Display board (component side)
Display board (LCD side)
LCD

For this replacement project all of these parts are discarded but I used the PCB as a template to make a new OLED mounting board our of a bit of copper clad board as follows:

Use original board as a template
Trace around it
and create a ‘plain’ replacement
Make sure it fits with the plastic surround (don’t lose the plastic lens)
Now position the OLED in the middle of the new board, I found a couple of small balls of blu-tak perfect for this, especially for getting the height and alignment right.
Line it up by eye
Then check it with the bezel
Once you are happy with it glue it in place.
I managed to buy some thin tinted plastic sheet
Made a darkened lens
Solder the cables and a bit of black tape to stop it showing through
New display is complete!

Connecting to the FT290

Find the keyboard unit PB-2238 P01 9 pin connector.
Snip off the yellow, purple and orange connections leaving the following: Pin 9 R40 Green, Pin 8 STD Brown, Pin 7 CE Red, Pin 4 R41 Blue, Pin 3 R42 White, Pin 2 R43 Grey
Connect to the Arduino
Tap into 5v (green wire, pin 4) P03 on the keyboard unit and ground at any solderable point on the chassis.
Connect the OLED and white meter LED via 100 ohms to D9
Add a 10uF decoupling capacitor on the underside of the Arduino.
Make an insulating pouch out of a bit of plastic sheet
Tuck the new assembly between the two front boards.

The finished article

Reassemble the case and its done!

The code

Click here for PDF

How it works

Display data is sent to the FT290R display in pairs of 4 bits (nibbles).

Each byte (pair of nibbles) is available when the CE bit is positive and is clocked into the Arduino with the falling edge of STD. You can see the data pairs in the diagram below where the STD pulses are close together.

The wider CE pulse spans the 12 STD pulses, representing 12 nibbles or 6 bytes

So, the above traces from my logic analyser represent the following sequence reading from left to right:

               Nibble 1       Nibble 2

Byte 6         0011           0101      5   

Byte 5         1101           0111      7   

Byte 4         0011           0011      3    This represents

Byte 3         0011           0100      4    5.437.5 on the

Byte 2         1101           0101      5    display

Byte 1         0010           0000      0   

Conclusion

I really enjoyed doing this project. It was great to be able to repair the FT290R I had. I have subsequently done a couple more.

I am happy to answer questions by email: nigel@rissoles.com

73’s G6RZR