Transistor as an oscillator

Your device is actually 2SD718 and can have possible substitutes as follows: BD245C, 2SC2681, 2SC2706, 2SC2837
BD245C 2SC684 KT819GM

Hi
the noise you hear is the RELAY circuit. the relay try to power up but they cant, because the oscillation circuit is defective thats why your power is not coming out! the main problem is the hot side section, the problem is the oscillation circuit.

NTE36 is allegedly equivalent.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/david_29ad5d1dd86564b0

Short circuit protection circuit operates. There should be a short circuit at its horizontal scan output section circuits. Check the horizontal output transistor for collector to emitter leak. Replace it with a new one of same number, and check. If you wish to get more details, http://electronicshelponline.blogspot.com/

All pins shorted together means the transistor is defective.

Generally, there are about 3 tests I usually do with ohmmeter to test a bipolar transistor:

1. Measure resistance from collector to emitter. If it is zero, transistor is shorted (bad).
2. Measure resistance from base to emitter. Should show conduction in one direction, but not the other.
3. Measure resistance from collector to emitter. Should show conduction in one direction, but not the other.

this website has lots of spare parts for semiconductors

http://www.appliedmaterials.com/parts/search_result/semiconductor/transistor

Hello

There is no horizontal oscillation drive pulse reaching the horizontal output transistor. There are so many reasons for this fault. Line drive transformer's primary winidng open, its load resistor has opened, line driver transitor fault, absence of horizontal oscillating signal from the Ic , Line Output Tranformer otherwise known as [LOT] fault and so on.

If you have a digital multimeter, capable of measuring frequency, the thins will be easy. Take the frequncey at the base of horizontal output trnsistor, which in turn drives the LOT. It should be around 15625Hz or so, with no video signal. With a transmission signal it will synchronise to 15625hz; in PAL system. Anyway desolder the horizontal output transistor from board, and check it for collector to emitter leak, first. If it has leak, replace it with same type and number. If it is Ok, come towards the line drive trnsformer, a small transformer directly soldered onto circuit board, very near to the above said LOT. which in turn drives the horizontal output transitor.
One end of its primary winding will go to the collector of the horizontal drive transistor, which will be a small one, and the other end to the supply point through a resistor. Check the voltage of the resistor point of line driver transformer, and the check the voltage of the other end, which is connected to the collector of the line drive transistor. There must be wome voltage difference, between these two points, say at about 3 volts os so. If so, pto this point is ok, and line drive transistor is working, and it gets the above said frequency. If not suspect the Ic.
Upto this point is ok, and still there is no oscillation at the line outoput, means fault is in the above said LOT. Replace it with same type and number.
There is an easy way to check whether LOT is working or not. If LOT is working, there will be Extra High Tension voltage coming to the final anode of the picture tube. You just place your forearm parellel to the face of the picture tube, just a centmeter away from it, and switch on the tv with its mains switch. If LOT is working and EHT is there, the hair on your forearm should be attracted towards the picture tube and can make sure that LOT is working. If so fault is surely to mainjungle Ic, and it should be replaced. OK.

Gopakumar. India.

Wharfedale pro bx1360sd

I have had problems with this stereo mixer amplifier which had the symptoms of no sound output from either channel .

I opened up the unit and discovered that the amplifier was correctly amplifying my input signal up to a relay which switches the output through to the speakers .

This relay did not activate at all.

When the power switch is turned ON you should hear a click approximately 2 seconds later , if no click then there is a problem with the circuitry associated with this relay .

I traced out all the connections associated with this relay and made a circuit diagram .

The relay is a 24v relay and I will explain the way that I can see that this section of the amplifier works.

It has been designed to ;

1. Create a slow start delay ( 2 seconds ) when the power is turned ON.

This it needed because otherwise there is a current surge and sparks from the relay turning on immediately.

1. Thermal cutout mounted on heatsink . If the ventilation fan fails the heatsink and transistors may get too hot and the cutout will operate and cut power to the relay by going open circuit.
2. Speaker protection from blown output transistors. There are 2 transistors q802 and q803 both 2sc1815. They are connected together emitter to emitter and collector to collector to form a differential Op amplifier I.C. If there is a blown output transistor then DC voltage will be detected by q802 and q803 and the relay will be switched OFF to protect the speakers .

Q804 turns On Q805 which turns On Q806 to activate the relay .

Voltages on transistors

Q802 and Q803 2sc1815

Base 0V Collector 12.9V Emitter 0V

Q804 2sa1015

Base 12.9V Collector 0V Emitter 15.1V

Q805 2sc1815 (driver for Q806)

Base 0V Collector 7.2V Emitter 0V

Q806 2sc1815

Base 0V at Turn ON then after 2 secs increases to 0.7V

Collector 2.8V ( transistor is activated as a switch Turned Fully ON ( saturated) to turn on the Load which is the relay .

Emitter 0V

I have replaced the following transistors to fix my amplifier q805 2sc1815 and q806 2sc1815 .If you are going to use a different type of transistor it may not work and also the lead connections of a 2sc1815 for the collector and emitter are different to those such as on a 2n2222( transposed).

It sounds like it could be biasing. Measure the DC voltage across the emitter resistors. If it's more than 0.001volts (1mV), reduce it to 1mV. The output transistors MUST be clamped to the sink when setting the bias current. Recheck the biasing after ~5 minutes of idling. The bias transistors (Q7, Q27) need to be in contact with the heatsink.

These amplifiers also have a problem with the shield ground fuse opening. This can lead to oscillation which can mimic biasing problems. You would need to use an oscilloscope to see the oscillation. You can check the shield ground. Disconnect the RCAs from the amp and measure the resistance from the shield of the RCA jacks to the center tap on the secondary side of the transformer. It should be ~0 ohms.

The first letter: A = Ge material semiconductors, B = Si material semiconductors, C = GaAs material semiconductors, R = Compound material. The second letter: A = Diode (low power, signal); B = Diode (variable capacitance)); C = Transistor (low power, audio frequency); D = Transistor (power, audio frequency); F = Transistor (low power, high frequency); L = Transistor (power, high frequency); R= control and swithching device); S = Transistor (low power, swithching); T = thyristors; U = Transistor (power, switching); X = Diode (varactor, multiplier); Y = Diode (rectifier); Z = Diode (zener). So the BC547 is a Silicon low power, audio frequency transistor. Hope that helps!