Hello everyone,
I need help. I am trying to restore a representative of the legendary NAD 3020A
I was able to restore it to working order. I replaced all of its electrolytic capacitors, cleaned it thoroughly (it was very dirty), greased all of the trim pots, and replaced the volume gain pot.
The amp worked well and I was happy with the sound quality.
When we tried to test it with some new KEF speakers of a colleague of mine, when increasing the potentiometer to 40-50%, a flame started coming out from inside.
After inspection and measurement - the two final transistors (2N3055 and MJ2955) and the pre-final transistors (2SD669 and 2SB649) were blown on one channel, the resistor 651 was also burnt.
I have replaced the above components and now when I turn it on there is no flame, but that is only because I have not connected a load to the output. On this same channel I currently have +30 Vdc, (while on the other I have 0 Vdc). Now if I turn any speakers back on they will either burn out or burn out the transistors again or both. Fortunately, the colleague's expensive speakers are sound.
Please advise where to look for the problem. Apparently something is keeping the end transistors fully open, but I don't know what causes them to be in that state.
After I restore it, I might think about a slight upgrade with speaker protection.
I need help. I am trying to restore a representative of the legendary NAD 3020A
I was able to restore it to working order. I replaced all of its electrolytic capacitors, cleaned it thoroughly (it was very dirty), greased all of the trim pots, and replaced the volume gain pot.
The amp worked well and I was happy with the sound quality.
When we tried to test it with some new KEF speakers of a colleague of mine, when increasing the potentiometer to 40-50%, a flame started coming out from inside.
After inspection and measurement - the two final transistors (2N3055 and MJ2955) and the pre-final transistors (2SD669 and 2SB649) were blown on one channel, the resistor 651 was also burnt.
I have replaced the above components and now when I turn it on there is no flame, but that is only because I have not connected a load to the output. On this same channel I currently have +30 Vdc, (while on the other I have 0 Vdc). Now if I turn any speakers back on they will either burn out or burn out the transistors again or both. Fortunately, the colleague's expensive speakers are sound.
Please advise where to look for the problem. Apparently something is keeping the end transistors fully open, but I don't know what causes them to be in that state.
After I restore it, I might think about a slight upgrade with speaker protection.
