How to troubleshoot this SMPS
AC fuse F501 blows off, as soon as the set is powered ON.
Check all the components marked in blue, for any short circuit. Check the two ceramic capacitors [C504 & C506 – 1000Pf IKV] for short circuit. There is possibility to get these capacitors shorted; if a high line voltage spike occurs. If any rectifier diode found damaged, replace all the four at one time. It is a good practice to replace the above mentioned capacitors too. The next possibility for the fuse blow, is the shorted junction [collector to emitter] of the SMPS switching transistor, 2SC4429L. It is best to resolder out this transistor; before doing any test further. I suggest taking it out, and checking it well for any leakage to its junction. Set the multimeter to measure Megohms range. Check the collector to emitter leak first. The resistance to this junction should be very high, that the meater can’t read. Even a slightest deflection can cause more damage, when the transistor is in circuit. So, if you see any leak to this junction, discard the transistor. Similarly, check the resistance between collector and base too. There shouldn’t be any leak to this junction too.
The set takes time to switch On. Sometimes, it might switch on after several attempts.
The main reason for this, according to my service experience; is the failure of one among or both the resistors that supply voltage to emitter of transistor V511 - 2SA1015. See, this voltage is derived from tha main rectified voltage; using R521 7 R520 – 100K resistors. If any one of this get open circuited, the set won’t start. This start voltage is also given to the base of the main switching transistor too via R522 – 15K resistor. Check this resistor too for open circuit.
If the B1 voltage output [109V] line has any short circuit, this type of SMPS won’t start. The control voltage to the opto-coupler is given from this voltage. So it is clear that, absence of this voltage means, there is no voltage to the Opto LED, which in turn controls the internal photo transistor of the opto-coupler. An another peculiarity to this type of circuit is, it wont start without any load. Here, a load resistor is actually used [R565 – 12K2W). Check this resistor for it resistance value.
In short, check all the components I’ve marked here. Check each of it out from circuit. Not in circuit. Replace the damaged component/s if any.
AC fuse F501 blows off, as soon as the set is powered ON.
Check all the components marked in blue, for any short circuit. Check the two ceramic capacitors [C504 & C506 – 1000Pf IKV] for short circuit. There is possibility to get these capacitors shorted; if a high line voltage spike occurs. If any rectifier diode found damaged, replace all the four at one time. It is a good practice to replace the above mentioned capacitors too. The next possibility for the fuse blow, is the shorted junction [collector to emitter] of the SMPS switching transistor, 2SC4429L. It is best to resolder out this transistor; before doing any test further. I suggest taking it out, and checking it well for any leakage to its junction. Set the multimeter to measure Megohms range. Check the collector to emitter leak first. The resistance to this junction should be very high, that the meater can’t read. Even a slightest deflection can cause more damage, when the transistor is in circuit. So, if you see any leak to this junction, discard the transistor. Similarly, check the resistance between collector and base too. There shouldn’t be any leak to this junction too.
The set takes time to switch On. Sometimes, it might switch on after several attempts.
The main reason for this, according to my service experience; is the failure of one among or both the resistors that supply voltage to emitter of transistor V511 - 2SA1015. See, this voltage is derived from tha main rectified voltage; using R521 7 R520 – 100K resistors. If any one of this get open circuited, the set won’t start. This start voltage is also given to the base of the main switching transistor too via R522 – 15K resistor. Check this resistor too for open circuit.
If the B1 voltage output [109V] line has any short circuit, this type of SMPS won’t start. The control voltage to the opto-coupler is given from this voltage. So it is clear that, absence of this voltage means, there is no voltage to the Opto LED, which in turn controls the internal photo transistor of the opto-coupler. An another peculiarity to this type of circuit is, it wont start without any load. Here, a load resistor is actually used [R565 – 12K2W). Check this resistor for it resistance value.
In short, check all the components I’ve marked here. Check each of it out from circuit. Not in circuit. Replace the damaged component/s if any.
This type SMPS circuit is used with many brand CRT TVs
Vertical scan output circuit
Full circuit
Used ICs: TMP8803 (System control chroma jungle) – TC4053 (Input selector) – ST24C16 (SYSTEM MEMROY) – LA4266 (Audio output) – LA78040 (Vertical Scan output)
