LF: Epson HX-20 service info

[Dave Dunfield]

Hi Tony,

>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.

Thanks for the useful information.

I am seeing only about 3.5v on C1/C6 ... and it has about a 1v DC
square(ish) wave superimposed on it. I see the same voltage/waveform at
the transistors, and on the voltage input to the LCD. The thumbwheel
does not affect it a whole lot - it mostly clips the tops of the square
wave.

Unplugging the LCD module makes little difference, so it's not a loading
issue (at least not from the module).

I see lots of very healty looking 5v square waves coming out of IC2C,
however I am having a great deal of difficulty trying to trace the circuit
on the board. Can you give me a bit more of the circuit?  Which pins
coming out of IC2C are driving the power supply, and what is the circuit
between these and C1?

Regards,
Dave
-- 
dave04a (at)    Dave Dunfield
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