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.
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.
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
