hi
i saw one sample for such tester and the people told 2n3904.
I see in forum in my country bc546 but dont see b. Can i do the replacement ?

 

They look like a good equivalent except that the current rating for the 2N2904 is 200mA and for the BC546 is only 100mA. As long as the collector current is less than 100mA then the exchange is good.

Note that the pin connections are reversed between these two transistors.

 

Forget about 'bc' prefix, manufacturer can write everything like C547, T547, S547 etc. In theory, The suffix 'B' (hFE rating category) could make difference however generally in general purpose, we can easily replace.

2N3904 and 547 Both can go higher than 100MHz with is great speed than an optoisolator. Also in the case of collector current, once I used the 547 transistor as constant current limiter and it was passing more than 300mA (triple than its max collector current rating) however it was not hot even little bit. I think during the modern days, the chip of the transistors are getting improvement. Or maybe in my careless part of the world, many transistors uses same common NPN chip, which is very far than its datasheet.

 

Just as offtopic/maybe/

Have used 1n4007 replacing 1n4001
bc546b replacing the transistor
and haven`t used On/Off Switch, supply directly

When put optoisolator and click the button the LED does light so it must be ok
no optoisolator and button > no light

LED for showing if the board is power supplyed doesn`t light never

That is interesting for me...what is the reason

 

Can you give us a schematic (or link to it)?

 

here it comes...

https://drive.google.com/open?id=0Bxome1ZSCRIadTBUaG54OGgtdzA

 

The possibilities for the power LED not lighting are:
1. The LED and its resistor are not connected.
2. They are connected to the wrong place.
3. The LED is reversed.
4. The resistor is the wrong value.
5. The LED or resistor are faulty.

Is this circuit built on a breadboard or stripboard?
Can you give us a photo of the actual circuit?

 

it`s that

https://drive.google.com/file/d/0Bxome1ZSCRIaNXRXekg5bjZfLUk/view?usp=sharing

 

it`s that

https://drive.google.com/file/d/0Bxome1ZSCRIaNXRXekg5bjZfLUk/view?usp=sharing

I can't make out much from that photo.
Do you have a meter? If so can you measure the voltage across the power LED.

 

This scheme Obviously does not like me

Have desoldered all and check all the elements. Have build again and check the connections after that

Have tried even with strong 9v battery.

The result : When Click the Switch ON the Power Led does light but no one from maybe 10 optois does light the LED2.

 

Are you sure your installing the optoisolator properly?

Your flash and the shiny bag made those pictures very unreadable. Try using indirect light and no flash.

p.s. I don't even know why they used the transistor in that circuit. The LED isn't drawing any appreciable current.

 

Now i am coming to work and begin check the connections on fresh head.

Most probably later will post again

 

Now it`s happening one thing that happened before...when turn it on a little! smell i feel. When touch the diode it`s very hot. If i think right before even the cathode was desoldered(maybe the leg was broken)

This is from short right? I saw the back side but see nothing

Thanks