BPL [SANYO] - GBR 9308 _ GBR-II 9308 (POWER SUPPLY FAULTS)
Power supply section to set has transistorised circuit. It have three
transisotrs at power witching side, and a control optocoupler.
Power switching output transistor used here is [Q313 - BU508AF]. Switching driver transistor is [Q312 - 2SC3807]. Error detector transitor is [Q311 - 2SA608]. Major fault to occur to this type of power supply is [1] Set won't switch ON, even though the protection fuse and all transistors are OK. [2] Protection fuse [F301 - 2AMPS 250VAC], blows of as soon as the set is switched ON.
To chec the fault described [1]. Check the voltage across [C307 - 100Mfd 450V = Main filter capactor]. It will be around 320VDc. This voltage can vary according to AC in voltage. Note the voltage at the catode of [D314]. ABOUT 12V must be present at this point. The voltage at this point is derived from main input DC voltage, via tw resistances in serial. This is the starting voltage to ths power supply section and should be noted first, if set refuse to switch ON. This is a common fault to this type of power supplies. Check the two resistors connected in series with main positive DC voltage [R320-120K & R321-120K]. Desolder out the one solder terminal of these reistor and chcek the resistor value with a multimenter set to measure MegOhms. It is best to replace both of these reistor with 1/2W ratings. If any one among these resistor fails, there will be no voltage to base of the switchiong power transistor, and base of swithing driver transistor. This is a main fault to this set.
The second one is with blown up fuse. Check all the four main rectifer diodes first [D301, D302, D303 & D304]. All of therm are (ERC-05). 1N 4007 diodes can be substitued. Unplug the degaussing coil plug from the main board first, and check the power supply section. If fuse blows out only when degaussing coil is connected, check the degaussing posistor. Repalce it. Check the main power switching tranistor [[BU508AF] for collector to emitter leak. If noted, repalce it. The collector to emitter resistance to this tranistor should be in several Meg Ohms. Even a slightest leak detected, replace it.
It is a best practice to repalce the optocoupler [D315 - PC817] too. The power supply circuit to this set is very simple to follow and to repair. No zener diodes are used with this power supply section.
The output voltages from converter transformer are [180VDC - To video output, 115VDC to Horizontal output and driver stages, 27VDC to Vertical output stage, 16VDC, Regulated 12VDC and 18VDC.
Power switching output transistor used here is [Q313 - BU508AF]. Switching driver transistor is [Q312 - 2SC3807]. Error detector transitor is [Q311 - 2SA608]. Major fault to occur to this type of power supply is [1] Set won't switch ON, even though the protection fuse and all transistors are OK. [2] Protection fuse [F301 - 2AMPS 250VAC], blows of as soon as the set is switched ON.
To chec the fault described [1]. Check the voltage across [C307 - 100Mfd 450V = Main filter capactor]. It will be around 320VDc. This voltage can vary according to AC in voltage. Note the voltage at the catode of [D314]. ABOUT 12V must be present at this point. The voltage at this point is derived from main input DC voltage, via tw resistances in serial. This is the starting voltage to ths power supply section and should be noted first, if set refuse to switch ON. This is a common fault to this type of power supplies. Check the two resistors connected in series with main positive DC voltage [R320-120K & R321-120K]. Desolder out the one solder terminal of these reistor and chcek the resistor value with a multimenter set to measure MegOhms. It is best to replace both of these reistor with 1/2W ratings. If any one among these resistor fails, there will be no voltage to base of the switchiong power transistor, and base of swithing driver transistor. This is a main fault to this set.
The second one is with blown up fuse. Check all the four main rectifer diodes first [D301, D302, D303 & D304]. All of therm are (ERC-05). 1N 4007 diodes can be substitued. Unplug the degaussing coil plug from the main board first, and check the power supply section. If fuse blows out only when degaussing coil is connected, check the degaussing posistor. Repalce it. Check the main power switching tranistor [[BU508AF] for collector to emitter leak. If noted, repalce it. The collector to emitter resistance to this tranistor should be in several Meg Ohms. Even a slightest leak detected, replace it.
It is a best practice to repalce the optocoupler [D315 - PC817] too. The power supply circuit to this set is very simple to follow and to repair. No zener diodes are used with this power supply section.
The output voltages from converter transformer are [180VDC - To video output, 115VDC to Horizontal output and driver stages, 27VDC to Vertical output stage, 16VDC, Regulated 12VDC and 18VDC.