Teac EU-34HT, Service Manual

2

DO NOT CHANGE ANY MODULE UNLESS THE SET IS SWITCH OFF

The mains supply side of the switch mode power supply transformer is live.

Use an isolating transformer.

The receivers fulfill completely the safety requirements.

Safety precautions:

Servicing of this TV should only be carried out by a qualified person.

- Components marked with the warning symbol on the circuit diagram  are critical for safety and must only be replaced with an identical

component.

- Power resistor and fusable resistors must be mounted in an identical manner to the original component.

- When servicing this TV, check that the EHT does not exceed 26kV.

TV Set switched off:

Make short-circuit between HV-CRT clip and CRT ground layer.

Short C804 (150mF) before changing IC802 or other components in primary side of SMPS.

Measurements:

Voltage readings and oscilloscope traces are measured under following conditions.

Antenna signal 60dB from colourbar generator. (100% white, 75% colour saturation)

Brightness, contrast, colour set for a normal picture.

Mains supply, 110VAC, 60Hz.

            PERI-TV SOCKET

SCART 1 (SC050)

1

Audio right output

0.5Vrms / 1K

2

Audio right input

0.5Vrms / 10K

3

Audio left output

0.5Vrms / 1K

4

Ground AF

5

Ground Blue

6

Audio left input

0.5Vrms / 10K

7

Blue input

0.7Vpp / 75ohm

8

AV switching input

0-12VDC /10K

9

Ground Green

10 -

11 Green input

0.7Vpp / 75ohm

12 -

13 Ground Red

14 Ground Blanking

15 Red input

0.7Vpp / 75ohm

16 Blanking input

0-0.4VDC, 1-3VDC / 75ohm

17 Ground CVS output

18 Ground CVS input

19 CVS output

1Vpp / 75ohm

20 CVS input

1Vpp / 75ohm

21 Ground

1.   INTRODUCTION

11AK26 is a 90ø chassis capable of driving 14” tubes at appropriate currents.

The chassis is capable of working in PAL M, PAL N, PAL B/G and NTSC M. The sound system is capable of giving 2.5 watts

RMS output into a load of 16 ohms.

2.   SMALL SIGNAL PART WITH TDA884X

The TDA8840/8842/8844 combine all small signal functions required for a colour TV receiver, except tuning.

2.1. Vision IF amplifier

The IF-amplifier contains 3 AC-coupled control stages with a total gain control range which is higher than 66dB.

The sensitivity of the circuit is comparable with that of modern IF-IC’ s. The video signal is demodulated by means of a PLL

carrier regenerator. This circuit contains a frequency detector and a phase detector. The AFC output is obtained by using the

VCO control voltage of the PLL and can be read via the I²C-bus. For fast search tuning systems the window of

the AFC can be increased with a factor 3. The setting is realised with the AFW bit.

Depending on the type the AGC-detector operates on top-sync level (single standard versions) or on top sync and top

white-level (multi standard versions). The demodulation polarity is switched via the I²C-bus. The AGC detector time-constant  capacitor

is connected externally. This mainly because of the flexibility of the application. The time-constant of the AGC system during positive