Fluorescent Display - Sony CDP-CX235 Training Manual

When the output of IC505 is LOW, these microprocessors are held in
reset and are inactive (apparently dead).
3.7Vac
A low AC voltage from power transformer T901 is applied to the filament
of the fluorescent indicator tube FL701.
-28V
The 41-ohm secondary winding of transformer T901 produces 31.7Vac
that is rectified by D505. The –40Vdc produced is regulated by Q501
using zener diode D506 for voltage stabilization.
The –28Vdc output from regulator Q501/emitter is applied to the fluores-
cent driver stage as the negative supply voltage and to one end of the
filament via D507as the tube's electron source.

Fluorescent Display

The FL701 Fluorescent Display tube needs the following to light a seg-
ment or a word in the tube:
•
Filament voltage
•
Positive voltage simultaneously applied to the grid and plate.
Basic Operation
The filament voltage comes from the power transformer T901 and the
positive pulses come from FL Driver IC701.
Just like a vacuum tube, the fluorescent display tube needs a source of
electrons. The electrons come from the filament, which is connected to
the –28V source. A controlling grid in the middle acts as a gate to deter-
mine if electrons should pass onto the plate to make it glow. At the gate,
a more positive voltage than the filament attracts the electrons and opens
the gate. A grid voltage that is the same as the filament will keep elec-
trons from leaving the filament so there is no glow.
The plate structures will be phosphorescent when struck by electrons. To
get the electrons to the plate, the plate must have a positive voltage to be
attractive.
Filament Grid
P1
Simple FL
Tube
P2
Structure
Plates
7
Grid & Plate Array
Within the FL tube there are 16 grid structures, each containing 36 plates.
Each grid structure produces a character or number by luminating a com-
bination of plates.
G1
P1 P4
P2 P5
P3 P6
P3
To make a specific plate glow, a grid structure is selected and a positive
voltage is applied to it. At that time, the plate structures that must glow
are also brought positive. In the diagram above, when G1 and P3 lines
are brought HIGH, the P3 plate in the G1 structure will glow. Even though
the P3 structure in the G2 structure is connected in parallel, receiving the
same voltage, it will not glow because the G2 voltage is LOW at this time.
The job of FL Driver IC701 is to create and time the grid and plate pulses.
Fluorescent Driver IC701
When the CD Changer is plugged into AC, Vcc is applied to IC701/pin 64,
starting its internal oscillator. The R-C parts that set the frequency of this
2.48MHz oscillator (16MHz is on the schematic) are located at IC701/
pins 58 and 59.
Also at AC plug in, the FL Driver IC701 is momentarily reset. IC505 mo-
mentarily holds its output LOW when +5V is input. This LOW resets FL
Driver IC701 when Vcc (power) is present at pin 64. The LOW lasts for
0.2ms (IC505) + 0.8ms (C507) = 10ms.
G2
Plate and Grid
P1 P4
P2 P5 Structures
P3 P6