Hi!
I've been trying to repair a technics su-v85a with a few problems. When I first got it it worked but the sound was awful so I went for a complete recap. That's when it really all went bad. I powered it up, set bias for voltage and current drive amp and let it sit for a while. After 25 minutes or so a funny noise and a lot of smoke took out the entire power amp sectionfor the right channel. the output transistors, as well as the drivers, some pre drivers, the vbe and even the IC on that channel were damaged. I replaced all of them as well as some resistors and diodes that shorted or went open circuit. The amp now fires up fine, both voltage and current driver amp lights come on and relay closes. I went over the whole power amplifier board and all the voltages are where they should be. After setting the two adjustments a quick test and yes, there is sound. So far the good news, bad news is one channel is louder than the other and after idling for about 20 minutes the current drive amp light went off again and relay opened. I immediately turned off the amp and found q516 to be shorted. Fortunately nothing else went bad so I changed Q516 and did the whole process over again. Amp fired up, all the voltages ok but after sitting 20 minutes, q516 died again. I know this is quite a complicated amp but if anyone can help I would be very grateful. (There is a good service manual on hifiengine).
I've been trying to repair a technics su-v85a with a few problems. When I first got it it worked but the sound was awful so I went for a complete recap. That's when it really all went bad. I powered it up, set bias for voltage and current drive amp and let it sit for a while. After 25 minutes or so a funny noise and a lot of smoke took out the entire power amp sectionfor the right channel. the output transistors, as well as the drivers, some pre drivers, the vbe and even the IC on that channel were damaged. I replaced all of them as well as some resistors and diodes that shorted or went open circuit. The amp now fires up fine, both voltage and current driver amp lights come on and relay closes. I went over the whole power amplifier board and all the voltages are where they should be. After setting the two adjustments a quick test and yes, there is sound. So far the good news, bad news is one channel is louder than the other and after idling for about 20 minutes the current drive amp light went off again and relay opened. I immediately turned off the amp and found q516 to be shorted. Fortunately nothing else went bad so I changed Q516 and did the whole process over again. Amp fired up, all the voltages ok but after sitting 20 minutes, q516 died again. I know this is quite a complicated amp but if anyone can help I would be very grateful. (There is a good service manual on hifiengine).
