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Looking for SA-8500II Advice

M

mchriste

Active Member
I picked up a SA-8500 II yesterday that looks great... sound doesn't match the looks. I think it's problem is dirty pots still... although I've cleaned the **** out of them. Left channel sounds good, right channel is very low and goes into protection with very little volume. DC offset is 2mv Right and 4mv left. I want to check bias, but I need to wire a resistor into the pre-out in to do this, the techpub says a 5.1kohm, and 8ohms in the speaker terminals. Question: what wattage for these resistors in this little test rig?


Additionally, poking around under the hood (which is very clean and nearly dust free) the only thing that jumped out at me was, on the switch assembly board, there is a trace in-between R49 and R54 that is brown, obviously got hot. The resistors adjacent to it do not look suspect. Any insight on that?


I'm obviously an amateur here but I like this stuff, not afraid to dig in.
 
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So I picked up some resistors and was able to set the bias. Left was close, right was low about 14mv brought it up to 30 and it stayed there for 30 min as per the instructions. Put some music through it and same story, right channel very low, if I bring the volume ups just a little relay opens up. Left is much better, no protection but the sound it distorted and in and out. Any ideas? I may disassemble the volume pot and really clean it. When I play with the volume it tends to clean up that left channel. Any thought on the relay?
 
So I can turn the volume up completely, dc voltage stays the same at the speaker terminals. Also no protection relay when I have just the meter on there. 2-8 mv
 
i suspect the overload circuit is coming into play when it shouldn't be .
try with no speaker loads or just connect a load to the good channel and see what happens
 
With no speakers, the relay never opens. With speakers on left and right, I can turn the balance over to left and the relay won't open, it only does it for the right side. Is that what you mean?
 
that narrows it to right channel only then .. the left working channel is a good reference point . will look at what those resistors do now to see if relevant .
 
narrowing this down is a little tricky for a beginner . i can see ways of doing this with the correct test gear . there are a couple of ways i see by looking at the schematics . if i had it in front of me i could see the easiest way to do this .
what is needed is isolating the amp from the protect circuit then testing the amp . it could be a fault in either circuit . you say vol is low so amp is in trouble or protect circuit might be at fault .
did you search for old threads with same symptoms ?
 
I did, but couldn't find the exact thing... Similar though. Lots of people end up finding bad resisters I think, be wouldn't I NOT be able to get the bias right if it was a resistor?
 
yes correct bias and offset generally means amp is healthy .
try measuring AC volts at speaker outs . nothing connected to inputs . this might not mean much but worth looking at .
 
I'm not totally. My meter has a diode function though, reads voltage differential right? And transistors I was reading a good thread about it earlier on here... I'd definitely have to refer to that
 
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