GRUNDIG Service
2 - 13
k
GDV 100 D
Descriptions
Power switch circuit
This circuit comprises MOSFET T7105, R
sense
R3110 and R3111.
Regulation circuit
The regulation circuit comprises optocoupler OK7116 which isolates
the error signal from the control IC on the primary side and a reference
component IC7215.
The TL431 (IC7215) can be represented by two components:
• a very stable and accurate reference diode
• a high gain amplifier
TL431 will conduct from cathode to anode when the refer-
ence is higher than the internal reference voltage of about
2.5V. If the reference voltage is lower, the cathode current
is almost zero.
The cathode current flows through the LED of the optocoupler. The
collector current of the optocoupler flows through R3115, producing an
error voltage, connected to pin 2 of IC7612.
Overvoltage protection circuit
This circuit consists of transistors T7121 and T7122, zenerdiode
D6123, R3124, C2120, R3121 and R3122.
When the regulation circuit is interrupted due to an error in the control
loop, the +5V output voltage will increase (overvoltage). This overvolt-
age is sensed on the primary winding 3-4. When the rectified voltage
over C2125 becomes higher than 20V, transistors T7121 and T7122
will conduct and the voltage on pin 1 of IC7115 will relapse. This results
in a switching off of the drain current of MOSFET T7105. C2121
discharges until 10V. The process of charging and discharging C2121
will start (hiccup mode), establishing a safe situation.
On/off circuit
This circuit is formed by R3261, C2260, D6260 and D6261, and an ON/
OFF switch. When the switch is open the supply is ON, when closed,
a negative voltage is fed to the optocoupler interrupting the regulation
circuit. This results in a switching off of the drain current of MOSFET
T7105. The supply is OFF.
Secondary rectifier/smoothing circuit
There are six rectifier/smoothing circuits on the secondary side. Each
voltage depends on the number of windings of the transformer.
The +5V is used as supply voltage for the regulation loop.
The SENSE input serves as reference for the reference component
IC7215 thus compensating the losses caused by the wiring to the
boards.
The +12V and -5V have separate voltage regulators (IC7205, IC7225).
The standby control signal coming from the SLAVE processor switches
off the +5V, +12V and -5V via transistor T7229 and MOSFETS T7206,
T7216, T7217, T7226.
+5VSTB is fed to the display board. On the display board, an extra load
(R3652 and R3653) keeps the PSU working during standby.
-40V is fed to the display board which is resending a voltage VGL-
(-30,7V). After 2,9V via regulator IC7256, this voltage is fed to
the display board (VGL+).
K
A
R
2.5V
+
–
Keyboard Control Unit
IC7600
TMP87C874F: USER microprocessor
Function Overview
TMP87C874F is a high speed and high performance 8-bit single chip
microcomputer, containing 8-bit A/D conversion inputs and a VFT
(Vacuum Fluorescent Tube) driver.
In this application, it is used as USER microprocessor and as VFTD
driver. All the communication to the digital board runs via the Serial bus
interface (I
2
C).
7600
6
5
15
16
26
27
28
29
30
31
32
34
35
36
37
41
14
12
11
17
18
20
21
22
42
43
44
45
46
47
48
49
50
51
10
25
23
24
4
74
73
72
71
70
69
68
67
66
65
3
64
63
62
61
60
59
58
57
56
55
2
54
53
1
80
79
77
76
75
13
39
38
40
78
7
9
8
19
33
52
TMP87C874F
SCL
SDA
VSS1
XOUT
XIN
RESETN
P22
P21
TEST1
P20
INT0
INT1
SCK0
PORT3
I C
2
VKK
COUNTER
PROGRAM
I/O PORT1
TIMER/COUNTER
I/O PORT6 (VFT)
VASS
VAREF
VDD
I/O PORT8 (VFT)
CONVERT.
8 BIT A/D
16 BIT
( RAM )
512X8 BIT
DATA MEMORY
TIMER/COUNTER
( ROM )
8kX8 BIT
INTERRUPT
CONTROLLER
I/O PORT7 (VFT)
( I/O PORT2 )
PROGR MEMORY
I/O PORT0
CLOCK/TIMING CONTROLLER
8 BIT
I/O PORTD (VFT)
I/O PORT9 (VFT)
I/O PORT5
I/O PORT4
C P U
Pin name
Function
INT0
external interrupt input 0
INT1
external interrupt input 1
RESETN
reset signal input, active low
SCL
I
2
C-bus serial clock input/output
SDA
I
2
C-bus serial data input/output
TEST
test pin, tied to low
VAREF
analog reference voltage input
VASS
analog reference ground
VDD
+5V
VKK
VFT driver power supply
VSS
ground
XIN, XOUT
resonator connecting pins for high-frequency clock
