Hi
I have been trying to repair a simple power supply from a student microscope base (3 of them in fact). It has a 230 to 12V transformer which gives a 12V AC input to the attached schematic (which I think is correct but I made it myself, so there may be errors - please correct me where needed).
My knowledge of electronics is very limited and I'm struggling to understand what role the transistor plays in the attached circuit (and if it is shown with the correct orientation).
I've attached photos of the board (the image of the rear side is flipped to match the top).
The good news is that I think I have identified the problem on 2/3 of the boards (new 7805's needed).
The last board is more difficult. I've replaced the 7805 and transistor (BC337) on this board but am now getting the LED permantly on and non-dimming, some odd voltage readings and a short across R1 (even without the resistor present) and I wonder whether I may have the transistor inserted the wrong way (even though it appears the same orientation as the original).
Any help much appreciated.
Cheers,
John
I have been trying to repair a simple power supply from a student microscope base (3 of them in fact). It has a 230 to 12V transformer which gives a 12V AC input to the attached schematic (which I think is correct but I made it myself, so there may be errors - please correct me where needed).
My knowledge of electronics is very limited and I'm struggling to understand what role the transistor plays in the attached circuit (and if it is shown with the correct orientation).
I've attached photos of the board (the image of the rear side is flipped to match the top).
The good news is that I think I have identified the problem on 2/3 of the boards (new 7805's needed).
The last board is more difficult. I've replaced the 7805 and transistor (BC337) on this board but am now getting the LED permantly on and non-dimming, some odd voltage readings and a short across R1 (even without the resistor present) and I wonder whether I may have the transistor inserted the wrong way (even though it appears the same orientation as the original).
Any help much appreciated.
Cheers,
John
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