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11min

LCD Circuit (Atari Lynx II)

NOTE: Here are my quick notes to help people diagnose the issues with no contrast on the LCD. Check your backlight tube is lit firstly or use a torch from behind to see the screen if not.

The job of this circuit is to send pulsing differential paired signals ranging from around 12 to 22V to the LCDs TPR2 and VSS/VDD pins (so two pairs of complimentary signals), whereby the higher the voltage the more the LCD crystals twist allowing more light through, and "turning on" the display.

To see a visual of all of the LCD pins checkout this YouTube video.

TLDR; Signals Overview

Pin

Signal Name

Signal

Voltage Range

1

5V

DC

5V

2

5V

DC

5V

3

DBL

3.146KhZ square wave

0 to 5V

4

P3

12.58kHz square wave

0 to 5V

5

P2

25.16kHz square wave

0 to 5V

6

P4 (HSYNC)

6.29kHz square wave

0 to 5V

7

P1

50kHz square wave

0 to 5V

8

VM

DC

1.4 - 2.7V (low voltage contrast)

9

CL2 (HSYNC)

158us pulses (6.29kHz)

0 to 5V

10

VD2

DC

2.2 - 4.4V (low voltage contrast)

11

CLOCK B1

39us of bursts low

0 to 5V

12

CLOCK A1

39us of bursts high

0 to 5V

13

CLOCK B2

39us of bursts low

0 to 5V

14

CLOCK A2

39us of bursts high

0 to 5V

15

CLOCK B3

39us of bursts low

0 to 5V

16

CLOCK A3

39us of bursts high

0 to 5V

17

DL1

Pixel data pulses

0 to 5V

18

DL3

Pixel data pulses

0 to 5V

19

DL0

Pixel data pulses

0 to 5V

20

DL2

Pixel data pulses

0 to 5V

21

RESET (VSYNC)

16.68ms low pulse

0 to 5V

22

LCDVDD

3.146kHz pulses

12 to 22V

23

LCDTPR2

3.146kHz pulses

12 to 22V

24

LCDVSS

3.146kHz pulses

-12 to -22V

25

GND

DC

0.74V

26

GND

DC

0V

5V and Ground Pins

Not much to say about these pins going into the LCD. Obviously the power and ground pins to drive the LCD driver IC integrated into the LCD ribbon.

DBL (Contrast) Pin

The DBL pin drives the starting point of the contrast circuit which ultimately generates the +/-22V rails of LCDVDD/TPR2/VSS.

Atari Lynx II DBL Pin
Atari Lynx II DBL Pin
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P1/2/3/4 Pins

The P1/2/3/4 pins to me look like a phase lock loop set of signals, to generate square wave forms of various frequencies likely used in the contrast and LCD circuit for displaying pixels.

VM/VD2 Pins

These are part of the voltage divider of the 5V rail to generate a low voltage version of the contrast wheel position.

Atari Lynx II VM/VD2 Pins
Atari Lynx II VM/VD2 Pins
๏ปฟ

CL2 (HSYNC) Pin

This pin is the 158us active high pulses for HSYNC which tells the LCD to start a new line.

RESET (VSYNC) Pin

This pin is the 16.68ms active low pulses for VSYNC which tells the LCD to start a new frame, for a 60fps redraw.

Clock Pins

The three groups of clock pins are used to drive each of the three driver IC chips installed on the LCD ribbon itself. They control one third of the LCD.

DL0/1/2/3 (Pixel Data) Pins

These are the 4 pins used to send actual RGB pixel data to the LCD. The pixel data is sent by the Hayato, but generated by the Suzy.

LCD VDD/VSS/TPR2 (Contrast) Pins

For more information about the contrast circuit that generates the +-22V signals for LCDVDD/TPR2/VSS, check out the Game Gear LCD Circuit topic which is covered in more depth, but has an almost identical circuit structure.

Follow the same diagnostics steps if you are missing the contrast voltages working forward from

Updated 21 Feb 2023
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LCD Interface (Atari Lynx II)
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TABLE OF CONTENTS
TLDR; Signals Overview
5V and Ground Pins
DBL (Contrast) Pin
P1/2/3/4 Pins
VM/VD2 Pins
CL2 (HSYNC) Pin
RESET (VSYNC) Pin
Clock Pins
DL0/1/2/3 (Pixel Data) Pins
LCD VDD/VSS/TPR2 (Contrast) Pins