DrDreas
Member
Hey guys,
So I am trying to get this AX-500 working, I've had one previously and really liked it and kinda regret selling it. This other one came along cheap and looks clean as, but the relay is not tripping. I've had a really quick look, but anything beyond simple and obvious I usually leave to my tech. I've searched via these forums and google to no real avail, but the following has been observed thus far:
I noticed I think it was C191 and 192 were bulging and open at the top so that was the first thing I addressed. I found a couple of caps the same value in my Onkyo parts mule (the two biggish grey ones on the pics) and that didn't do anything, but the strange thing is they are getting quite hot. This leads me to assume the problem is not the caps but whatever was responsible for wrecking the others I replaced.
The area surrounding Q113,117 and 111 seems to be getting hot also, if the darkness around that area is any indication
At this point I have taken it to my repair guy. He says there is around 6vDC offset and I think he referred to a "ripple current" that is present in a lot of places? He noted C201 (the greeen one?) and mentioned that he couldn't clearly identify it's function, that the output transistors were not the problem and that whatever was going on was not specific to the left or right channel.
Here are some excerpts from the service manual
Now I found this bit of text that poses a question relating to it:
"Does anyone understand the unusual VAS current loading arrangement used here? The voltage amplifier stage is loaded by a current mirror. Unusually the input side of the current mirror is programmed by R208 and C197, via Q117. The base of Q117 is biased mid way between the base of the two driver transistors, Q121 and Q123. The other side of R208 and C197 is bootstrapped to the output rail via electrolytic capacitor C201. It looks like some kind of feed-forward error correction around the output stage. Or maybe there is another logical explaination why this arrangement is used. Any comments?"
And also this from another AK thread relating to this amp:
Not being much of a tech myself I have no idea, but am hoping this triggers a piece of info someone with some experience on this or similar Yamaha model may have. The reason I like this tech is that he is very honest and open about work he performs, plus his experience usually means he is very quick at troubleshooting...and less time spent with trial and error removal and testing of components means I usually avoid the "arm and a leg" repair charges these guys can be notorious for! but he's feeling like a lot of time could be wasted here on something that turns out to be simple so I'm hoping to help narrow it down for him and save some cash! Is there anything obvious that I could pass on to narrow down the list of culprit components here?
Many thanks in advance
So I am trying to get this AX-500 working, I've had one previously and really liked it and kinda regret selling it. This other one came along cheap and looks clean as, but the relay is not tripping. I've had a really quick look, but anything beyond simple and obvious I usually leave to my tech. I've searched via these forums and google to no real avail, but the following has been observed thus far:
I noticed I think it was C191 and 192 were bulging and open at the top so that was the first thing I addressed. I found a couple of caps the same value in my Onkyo parts mule (the two biggish grey ones on the pics) and that didn't do anything, but the strange thing is they are getting quite hot. This leads me to assume the problem is not the caps but whatever was responsible for wrecking the others I replaced.
The area surrounding Q113,117 and 111 seems to be getting hot also, if the darkness around that area is any indication
At this point I have taken it to my repair guy. He says there is around 6vDC offset and I think he referred to a "ripple current" that is present in a lot of places? He noted C201 (the greeen one?) and mentioned that he couldn't clearly identify it's function, that the output transistors were not the problem and that whatever was going on was not specific to the left or right channel.
Here are some excerpts from the service manual
Now I found this bit of text that poses a question relating to it:
"Does anyone understand the unusual VAS current loading arrangement used here? The voltage amplifier stage is loaded by a current mirror. Unusually the input side of the current mirror is programmed by R208 and C197, via Q117. The base of Q117 is biased mid way between the base of the two driver transistors, Q121 and Q123. The other side of R208 and C197 is bootstrapped to the output rail via electrolytic capacitor C201. It looks like some kind of feed-forward error correction around the output stage. Or maybe there is another logical explaination why this arrangement is used. Any comments?"
And also this from another AK thread relating to this amp:
Not being much of a tech myself I have no idea, but am hoping this triggers a piece of info someone with some experience on this or similar Yamaha model may have. The reason I like this tech is that he is very honest and open about work he performs, plus his experience usually means he is very quick at troubleshooting...and less time spent with trial and error removal and testing of components means I usually avoid the "arm and a leg" repair charges these guys can be notorious for! but he's feeling like a lot of time could be wasted here on something that turns out to be simple so I'm hoping to help narrow it down for him and save some cash! Is there anything obvious that I could pass on to narrow down the list of culprit components here?
Many thanks in advance
Last edited: