Used ICs: TEA1533AT (SMPS controller),
TF6NK90Z (SMPS switching FET), PT11400 (Remote control IC), TDA9570 (Syscon
Chroma Jungle), TDA1517 (Audio output IC), LA78040 (Vertical scan output IC),
BU1508DX (Horizontal scan output transistor)
This circuit have been used with
many brand CTVs. The main fault found
with this circuit is the breakage of the Horizontal scan output transistor
(BU15508DX). If this transistor is found
leak (Collector to Emitter), be sure to measure the frequency at pin number (30
– HOUT) of IC TDA9570H. {If the set does not turn ON, and the main fuse on board is OK, is the symptom of horizontal output trannsitor damage. The power LED at the front panel of the set will flash once, and will immediately go off - (Short circuit protection).In this case, just de-solder out the horizontal output transistor, and switch ON the set without it. The power light should turn ON and remain lit; provided there is no fault with it's circuit. You can measure all the SMS out voltages now} In most cases this frequency will vary much higher than normal.
If you found this frequency to be very high (it can be measured without
inserting a new horizontal transistor in place), make sure it to be under
limited frequency; usually between (15500 to 17800 Hz), before replacing the
horizontal output transistor, otherwise the transistor will get damaged again,
as soon as you switch ON the set, not giving any chance to you checkout the
fault. Check and make sure the freewheeling capacitor, that connected in between the collector of the horizontal output transistor to Ground is good. Make sure the solder terminals of this capacitor have no loose solder at all. If this capacitor (usually a 0015 to 0047MFD-2500VDC.) is not good or having a loose solder terminal, the transistor will get damaged.
More to say, if the deflection yoke (Horizontal scan side winding) have
an internal short in between its windings, this transistor will overheat in no
time, and will fail. So after replacing
this transistor, check the heat of the transistor, periodically at about 2 minute’s
interval. It might get warm, but not too
hot. Feel this heat at its heat-sink.
Click on the schematic to magnify
Another possibility is with DC output voltage from the SMPS converter. If this voltage go beyond normal [High], the
transistor will get damaged. If you
found this voltage to be abnormal, check and clear all the faults with the SMPS
circuit first.
The components used in the SMPS of this circuit are cheap and easily
available at the local electronic spare part market. When work with it, just replace
all the main components; (SMPS switching transistor, the opto-coupler and the
control IC (TEA1533), all at the same time.
