hi all, new guy & first post here, hoping to pick the collective Brain to help me with an issue im having with my pioneer sa620 🙂
I have a pioneer sa620 amp that I recapped about 12 months ago, and until 3 days ago has been purring along perfectly......it now has a low volume level distortion issue on the right channel only. so far (with no improvement) I have:
searched for cold/dry joints
removed and tested both main output transistors and they seem within spec and fine, replaced anyhow just, well, im home recovering from spinal surgery so hey, I got plenty of time and boredom to overcome lol, I've replaced every component in the bias circuit for the right channel, I've replaced every single diode and zener in the entire unit, every transistor in the amp & preamp circuits and also the power supply circuit I've also RE-RE capped the entire unit (yea yea don't judge, like I said im home for 6 weeks recovering, and I have plenty of time and spare parts / components to play with lol! but after all that still no improvement, the right channel low level distortion and zero idle current remains!
I will add that this issue is also present through headphones, and switching to MONO also makes no improvement or difference.
idle current on the left channel is sitting happily at around 25mv the right channel though is a flat zero 0.00mv
im no expert but an avid hobbyist who loves playing around with this stuff and im not afraid to give anything a go, I've searched and scanned the forums but unless im looking in the wrong spot I've not found anything of assistance. hoping the collective brain out there could steer me in some sort of direction. thanks in advance guys.
Pioneer SA-620 Stereo Integrated Amplifier Manual | HiFi Engine
I have a pioneer sa620 amp that I recapped about 12 months ago, and until 3 days ago has been purring along perfectly......it now has a low volume level distortion issue on the right channel only. so far (with no improvement) I have:
searched for cold/dry joints
removed and tested both main output transistors and they seem within spec and fine, replaced anyhow just, well, im home recovering from spinal surgery so hey, I got plenty of time and boredom to overcome lol, I've replaced every component in the bias circuit for the right channel, I've replaced every single diode and zener in the entire unit, every transistor in the amp & preamp circuits and also the power supply circuit I've also RE-RE capped the entire unit (yea yea don't judge, like I said im home for 6 weeks recovering, and I have plenty of time and spare parts / components to play with lol! but after all that still no improvement, the right channel low level distortion and zero idle current remains!
I will add that this issue is also present through headphones, and switching to MONO also makes no improvement or difference.
idle current on the left channel is sitting happily at around 25mv the right channel though is a flat zero 0.00mv
im no expert but an avid hobbyist who loves playing around with this stuff and im not afraid to give anything a go, I've searched and scanned the forums but unless im looking in the wrong spot I've not found anything of assistance. hoping the collective brain out there could steer me in some sort of direction. thanks in advance guys.
Pioneer SA-620 Stereo Integrated Amplifier Manual | HiFi Engine
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You think that may be the culprit?? It’s literally just about the only thing that hasn’t been replaced lol
Have yo some trim resistors on the pcb ? There are none on mine but I have the previous generation with the screens ampermeters not the leds where the biasing was made by a wire per channel... often on the 80s and more the trim resistors made of carbon comp suffer... has to be tested if you have one per channel cause it costs nothing.
can you compare the voltage readings between the good channel and the
bad one (with a DMM)?
there should be a difference somewhere...........perhaps around the bias circuit,on the diodes, res and so on.
bad one (with a DMM)?
there should be a difference somewhere...........perhaps around the bias circuit,on the diodes, res and so on.
It is possible that a resistor is faulty. Try tapping the board with the end of a pencil to see if that provokes anything. If it does nothing, tabulate all the voltages at the transistor legs for left and right channels. Begin from the power transistors and work towards input stages. Stop when there ceases to be a difference.
If I had to make a stab I would check R56, R64, R124 values.
If I had to make a stab I would check R56, R64, R124 values.
thanks so much for the assistance guys its appreciated!
so when checking all these trans voltages, do I do It (procedure wise) like I would to measure idle current? (vol min, no inputs connected, no speakers, give a warm up time etc etc?) thanks again 😀
so when checking all these trans voltages, do I do It (procedure wise) like I would to measure idle current? (vol min, no inputs connected, no speakers, give a warm up time etc etc?) thanks again 😀