Servicing Information; Horizontal Deflection And High Voltage Production; Horizontal Driver - Loewe Q2500B Serviceanleitung

Technology of Q 2500 colour TV set
2.2.9

Servicing information

For repairs and fault-finding in the power sup-
ply unit the following should be noted:
Always connect the unit via an isolation trans-
former, especially when fault finding the pri-
mary side.
The load on C 620 remains active long after
the unit has been switched off. Discharge the
load if necessary via a low-resistance resistor.
Operation of the power supply unit without the
digital unit is possible. For this pin 5 on pin
connector W 8181 is connected to earth, but
not until a voltage is applied to the standby
power supply. For specific failures, this test
can also be done with an integrated digital
component.
A check of the horizontal output stage cannot
be made by withdrawing the deflection plug.
For this test L 534 must be unsoldered. An
extra load is not required.
A separate test of the power supply unit func-
tion without interference from the chassis can
be achieved by unsoldering one side of the
secondary side rectifier diodes. The rectifier
branch for the UB (D 651) and U7 (671) must
be available. The UB can then be loaded with
a 100 Watt LED.
U 7 and UB are necessary for power supply
control, so do not deactivate them.
2.3 Horizontal deflection and high
voltage production
On the 100 Hz Chassis Q 2500 the horizontal
driver, horizontal output stage and high volt-
age production are essentially the same as
the predecessor.
Document Q 2500
2.3.1

Horizontal driver

The horizontal driver stage is controlled from
I 2521 on the signal board via pin 13 from
connector W 1511. The pulse at this point is
2.5 Vss.
U25
R521
!
C521
R527
C527
C528 D527
C526
D526
R526
C524
U5
R1044
R2563
Q2561
R2561
R2558
R2562
Capacitive control via C 524 prevents driver
stage Q 526 being held conductive continu-
ously if components are faulty or there are no
control pulses. Diode D 526 enables rapid
discharge of C 524, if Q 526 is controlled in
the blocking phase.
21
D532
T528
R532
R533
Basic board
Q526
Signal board
Video /
Q2556 R2557
deflection
H
Q2951
DEFLECTION
U5
© Loewe ProCollege
T531
Q534
UB
I 2521
processor
8
79
I 2801
CCU