LF: Epson HX-20 service info

[Tony Duell]

> 
> Anyone have service information on the Epson HX-20?
> 
> Specifically looking for information on the LCD driver.
> I have an HX-20 in which the LCD has grown very dim ...
> appears blank from normal viewing angle, but is barely
> readable at very low angle...

I have the hardware technical manual...

Firstly, a pinout of the tapewire to the LCD module (it plugs into the 
keyboard PCB).

1 Gnd
2 CS0/ These are the chip select lines for the
3 CS4/ 6 LCD driver chips (7227)
4 CS2/
5 CS1/
6 CS3/
7 CS5/
8 Reset
9 Clk
10 C/D (Command/Data select)
11 SI (Serial In)
12 SCK/ (Shift clock)
13 SO/Busy (serial output/busy line)
14 Vcc (LCD supply voltage)

The LCD driver chip is actually a standard, not custom, part. NEC 
uPD7227. I have a data sheet on it I think.

Now, I would start by checking that LCD supply voltage signal. It starts
on the main board where IC 2C (4049) acts as an oscillator and driver to
operate a voltage doubler, You should see about 7V (I think) on the +ve
end of C1 or C6. This then goes up to the keyboard, to a 2 transistor 
voltage controller circuit there. Check for an adjustable voltage (set 
with the thumbwheel on the side of the machine) at the emitter of Q2 on 
the keyboard. This voltage, BTW, is fed back to the mainboard to power 
some of the ICs that connect to the LCD driver chips.

> 
> Also, anyone on the list with a working HX-20 who would
> be willing to open it up and take some voltage/waveform
> readings for me (you will need an oscilloscope)?

Setting it up near a 'scope would be a pain, but I can do voltage 
readings or logic analyster traces if you think that would help.

-tony