Akai DV-R4025VSS, Service Manual

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PT6311 S0791GC There are 3 different devices operated by the and (Optional):
* Vacuum Fluorescent Display (VFD)
* Push-buttons
* VFDs
There is an option for a tray lamp and a joystick which is not currently assembled. The VFD display is
custom made,
implemented in a 6 grids by 16 segment matrix.
The VFD needs special voltage supply for operation:
* Vkk which is -21V needed to drive the segments and grids of the VFD.
* Vf1, Vf2 which powers the exectron cloud filament (cathode) with a differential voltage of 3.5V. This is
a floating
voltage difference generated by the power supply, and is biased to -21V in the ront panel board by a
Zener circuit
from the -21V (Vkk) supply. Moving the bias towards a more positive number will reduce the segment
brightness.
Vf1 & Vf2 provide a DC supply to the cathode. To overcome the voltage difference between one end
and the other
of the cathode, it is geometrically titled so that the segments observe the same potential and have all
the same
brightness. Other way to overcome the problem is to employ an AC supply to power the Vf1 and Vf2.
4.3 SMPS
The mains power(220VAC) fed from K1is filtered through 3C1, 3L1, 3C2 then rectified by D1,D2, D3 and
D4 and generates an output at 300VDC. This 300VDC fed to 3TR1 (pin1, pin5) which
connects to 5M02659R(pin3), then 5M02659R will automatically generate a 50KHz square waveform,
this 50KHz square waveform controls the ON/OFF between 5M02659R pin1 and the ground.
In normal condition, T1 primary (between pin2 and pin4) will create a 50KHz square waveform
which is controlled by 5M02659R, this signal then fed to 3TR1 and generates 2 different potential
voltages of 12V and 5V .The 12VDC and 5VDC
then rectified by3D11 and then filtered by3 L2, 3R9, 3C18, 3CC25 and 3C11. The feedback voltage
is controlled by Ic3 TL431 and IC2 PC817. When the output voltage is higher than 5V, the voltage at
TL431(2.5V) is compared with R10 and send out a signal to 5M02659R, the output square waveform then
will change to adjust the output voltage, this acts as a voltage stabilizer.
1
4.2.1 Front Panel Interface
6 Pin, Data Connector Pin Assignments
PIN NAME I/O DESCRIPTION
1 DATA I IR sensor interrupt
2 CLK O Front Panel chip select
3 STB O Front Panel clock
4 GND O Front Panel Data output
5 VCC
6 REM I Front Panel Data input
PIN NAME FROM DESCRIPTION
1 VFD 1 SMPS Segment and grid Voltage of the VFD
2 VFD 2 SMPS Provide a DC supply to the cathode. To vercome
the voltage difference between one and the other of
3 -21V SMPS the cathode.
3Pin, Power Connector Pin Assignments
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