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...then most commonly, the problem is simply that the LCD contrast trimmer R47 has not been adjusted. This is a very
sensitive adjustment (though easier to adjust from PCB Rev 3 onwards). Do not be tempted to assume that the voltage on
the contrast pin of the LCD should match the one shown in the manual - it will vary from LCD to LCD.
If adjusting R47 still doesn't bring visible text to the display, then check with a DVM that you can see the voltage at the
LCD contrast pin (pin 3, i.e. 3rd from the left) does vary from 0 to 5V as you turn R47.
If you see the voltage varying correctly from 0 (full anti-clockwise) to 5V (full clockwise) as you turn R47, then there could
be a DIFFERENT problem.
Check with a DVM that there are no short-circuits between adjacent LCD pins, or between any LCD pin and Gnd or Vcc.
Check for continuity between each LCD pin and the corresponding pin on the processor. You can do this with the board
upside down, and the LCD module plugged in.
If ALL of that checks out fine, then there is one more possibility for a blank screen, in firmware versions up to and
including 1.00e. In these versions the firmware carries out initialization steps which clear the screen. Then it tries to
communicate a command to the Si5351A Synthesizer chip IC1. The commands to IC1 are sent over an I2C serial
communication link. If for some reason, the Si5351A does not respond to the command to acknowledge it, then the I2C
bus will hang up while infinitely waiting for the response of the Si5351A. The screen will remain blank indefinitely and
mislead you into thinking there is a problem with the processor or the screen. So it is worthwhile to check the Si5351A
soldering, preferably with a jeweler's loupe or one of the inexpensive USB microscopes, if you have one. Check for solder
bridges between pins, mis-soldering, a loose pin, or any other sign that the 10 pins of the Si5351A are not properly
connected to the PCB.
Hopefully after all this, you will find the solution to the blank screen.
LCD top row is blocks, bottom row is blank
If the screen looks like this...
...then be aware that this is the default state of the LCD module at power-up, if nobody has told it to do anything. It
indicates that the processor has not issued any commands to the LCD. This is usually because the processor is not
running. If the processor is not present at all, the LCD will look like this too. So though it sounds silly, do check that in your
excitement you didn't forget to install the processor ;-) Also check that the processor is installed correctly - the dimple at
one end of the processor must face to the right side, where it will match up with the dimple indicated on the PCB
silkscreen (white print).
