Has a lot of years used in TVs power supplies, representing a pulsed sources, which converts the high DC voltage (about 300 V) in a row is also constant output voltages other (usually smaller) values of, for example, 125, 60, 25, 15, etc.
High voltage derived from AC (50 Hz) AC 220 V, using a full-wave rectifier, and the output voltages from the pulse, a relatively high repetition rate (tens of kilohertz), formed mainly on the secondary windings of the power transformer.
Between these nodes included rather complex switching Converter that specifies a portion of which is collected on a chip or transistors, which often fail. And it is not always possible to immediately find the necessary new parts to replace defective ones.
Fig. 1
In order to get the TV to work, you can temporarily create a very simple switching Converter according to the scheme shown in Fig. 1. In the left of the output power transistor VT1 (the PSU or replaced your defective or the equivalent) the conclusions of the collector and the emitter of which is connected to the existing circuits of the TV. Connection for TV shows "Youth CD", and all the nodes specifying the inverter PSU need to be disconnected from the base of the transistor. Of course, in another TV collector circuit of the transistor may look different, but they are left unchanged.
The base circuit of the transistor VT1 is collected according to the presented scheme. It used elements R2 (R28 numbering in the TV), VD1 (VD10), VD2 (VD11) from PSU TV on and change new additional parts R1, R3, C1. The capacitor C1 is K73-9 for a voltage of 100 V.
Fig. 2
As a result of such Converter is a blocking oscillator, waveforms of voltages at characteristic points which can be seen in Fig. 2 when using the device in the above TV. In other apparatus in which applied other transformers, waveforms may be slightly different.
Transistor VT1 is installed in an existing PSU heatsink. In addition, the heat sink screws additional metal plate, which increase the scattering cross-section is approximately twice.
To install the Converter in the nominal mode, you rotate the engine tuning resistor R2 to obtain the required voltage power line scan - in our case 125 In the output of the rectifier in the secondary circuit.
It should be reiterated that the use of such a Converter is a temporary measure, as the stability of the resulting stresses will be low. As a result when you change the brightness of the image changes a little and its size.
Author: L. Kononenko, Moscow; Publication: www.radioradar.net