Hello everyone,
I guess I need help from the masters to try and find what is frying a 2SC5669 transistor on the left channel of this front center Amp for a NAD T752.
Was working perfectly and all of a sudden I heard a pop, and then a glow from the amp. Not only did the 2SC5669 burn a leg, but R520 which is a 220 ohm resistor partially burned - it now measures 110 ohms.
I bought this amp second hand fairly cheap as it was not working, it went into protection mode. I finally traced it down to the same transistor Q510, the one that just popped. It was shorted and so was the paired Q509 2SA2031. I replaced them both along with Q507 (2SC4159E) and Q508 (2SA1606E). I also changed Q511 which is a 2SC2362 which was shorted. Checked every other component on the board for the left channel, removed every transistor and checked them with my transistor checker, checked all caps and changed a few out of range, all resistors, etc. Everything looked fine so reinstalled and it was back to life!
It played for approximately 4 hours with a beautiful sound. I checked and set the idle current on each channed to 1mV and all was good. After listening to a track fairly loud, is when it popped as shown in the pictures.
Any ideas what might be drawing so much current on R520 to scorch it and what might be making Q510 pop again? Many thanks for any input, as I'd love to get this amp back to life, it sounds so beautiful!
I guess I need help from the masters to try and find what is frying a 2SC5669 transistor on the left channel of this front center Amp for a NAD T752.
Was working perfectly and all of a sudden I heard a pop, and then a glow from the amp. Not only did the 2SC5669 burn a leg, but R520 which is a 220 ohm resistor partially burned - it now measures 110 ohms.
I bought this amp second hand fairly cheap as it was not working, it went into protection mode. I finally traced it down to the same transistor Q510, the one that just popped. It was shorted and so was the paired Q509 2SA2031. I replaced them both along with Q507 (2SC4159E) and Q508 (2SA1606E). I also changed Q511 which is a 2SC2362 which was shorted. Checked every other component on the board for the left channel, removed every transistor and checked them with my transistor checker, checked all caps and changed a few out of range, all resistors, etc. Everything looked fine so reinstalled and it was back to life!
It played for approximately 4 hours with a beautiful sound. I checked and set the idle current on each channed to 1mV and all was good. After listening to a track fairly loud, is when it popped as shown in the pictures.
Any ideas what might be drawing so much current on R520 to scorch it and what might be making Q510 pop again? Many thanks for any input, as I'd love to get this amp back to life, it sounds so beautiful!
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