wega v-4810 (sony ta-5650 v-fet) right channel lower volume and missing low frequencies dead v-fets? (problem isolated to the power amp section)

[TrevorBarten]

I bought a v-4810 for not a lot of money and I wanted to keep it for myself, however the right channel is not working correctly. I did some testing and sadly the issue lies in the power amp section. Could someone tell me if there is a way to know whether this is caused by defective v-fets or not? Was planning on doing a recap and giving the amp a general service like replacing the ' killer diodes ' among other things (to my capabilities anyway), but if the v-fets are kaput it seems like a waste of time. I also have a fully working ta-4650 in use so I guess I would have an entire set of extra v-fets if the right channel is indeed dead but I would assume that if the transistors are bad it wouldn't come out of protection no? Or is that just wishful thinking? I would like to mention that the right channel does not sound distorted, it's just missing the lower frequencies and is a lot lower volume (still gets to listenable volumes it's not barely hearable levels of low).

 

[chazix]

missing the lower frequencies and is a lot lower volume (still gets to listenable volumes it's not barely hearable levels of low).

I don't know this amp, but these symptoms don't sound like bad V-FETs. Degraded capacitor(s) in the input coupling or feedback degeneration positions could cause it (but I'm guessing as to whether this amp even has those components).

 

[gadget73]

I'm also not specifically familiar with vfets but I've never heard of an output device that had a frequency-dependent failure mode. Low gain and response problems could very well be failed cap(s) in the feedback loop though.