A surround amplifier with no sound output repaired. Model Vtrek AV-3100
I got a call from the principle of the Lutheran school in my area to go and check the amplifierin their school theater. When I got there, and powered all the equipment, I could see there was a standby light but there was no sound coming out of the speakers; not even a hiss sound.
It is an old amplifier but a very good quality one.
As you can see, the standby light is on and the panel is on as well.
A few screws were off and the inside board was exposed.
The moment I scanned the board with my naked eye, look what I found.
That was an obvious sign of some bad transistors. The first thing that came to my mind was what part number is that blown transistor?
Here is a close look of the blown transistor. When I got closer with my x10 magnification, I could see that part number of this blown transistor was printed on board. I also found out later on that there was another transistor shorted next to this blown one. The part numbers are: TIP42C and TIP41C. It was a push pull amplification.
If you measure voltage across these transformers, you would get negative and positive readings. I could not find the actual part number so I had to use replacement for them. They were: BD244C and BD243C. After replacing these parts, I looked for more shorted or blown parts and look what I have found.
A 220 ohm resistor, a 2n5401 and 2n5551 transistors were found blown and shorted on the same line of the other transistors were found before. As you can see in the photo, the part numbers are printed on the board. All these blown and shorted parts were replaced with the same part numbers and when I powered up the device, everything worked nicely.
As you can see, all these parts were replaced on this old but nice amplifier. I forgot to mention that the main fuse (5 amps) was open as well, but I could not locate it to take picture of it simply because it was blown to pieces.
I took it back to the Lutheran school and installed it back in the theater there and everything worked just fine. Mission accomplished.
This article was prepared for you by Waleed Rishmawi, one of our ‘Master Authors’ and currently working in the Bethlehem area of Palestine repairing electrical and electronic equipment.
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