SA-9500II Input Signal Problem

[Noodle]

I have an SA-9500II that has a "tuner input" problem. With an audio source I can hear the right input signal but it is lower than the tape's or aux's normal signal level. And, the left channel has no audible signal at all. This is in "stereo" mode.
I can switch the mode to "rev" mode and the right input signal goes to the left channel. Switch to "L+R" and the right signal goes to both channels. Switch to "L" and of course, I get no audio thru either left or right speaker.
Again this is thru the tuner input only, all other inputs work as they should, except phono 1 & 2 inputs have not been checked. No turntable available at time of check.

Any ideas what the problem could be?
Thanks.

 

[markthefixer]

YES, download the service manual and look at R35 & R36, find them in the chassis on the equalizer amp assembly, near the function switch on the board.

When NOT selected the phono inputs are grounded through a 47 ohm series resistor. Too much voltage will fry the resistor, resulting in anything from low signal to no signal.


This thread details it:
http://www.audiokarma.org/forums/showthread.php?t=98733

An incredibly bad wiring error? It takes a lot of energy to do this:

 

[Noodle]

Thank you sir, I'll take a look at this.

 

[Noodle]

Mark,
I have looked at this and my situation is near identical to what your picture shows.
The only difference is that R38 and R2 have a little more charring/black on them than in your pic.
Also, my R37 is not as burned as the R37 is in your pic.
I have checked R35 & R36 with my meter and neither of them are nowhere near 47 ohms. I also checked R37 and R38 and they are registering 47 to 48 ohms.
I guess next would be to replace R35 and R36, but I will wait until I hear back from you. I'm not to knowledgable on this electronic thing but am willing to learn.
Thanks.

 

[markthefixer]

Mark,
I have looked at this and my situation is near identical to what your picture shows.
The only difference is that R38 and R2 have a little more charring/black on them than in your pic.
Also, my R37 is not as burned as the R37 is in your pic.
I have checked R35 & R36 with my meter and neither of them are nowhere near 47 ohms. I also checked R37 and R38 and they are registering 47 to 48 ohms.
I guess next would be to replace R35 and R36, but I will wait until I hear back from you. I'm not to knowledgable on this electronic thing but am willing to learn.
Thanks.

Yes, replace them, it's a bit of a pita to get at them. Check the nearby switch wafers for burning as that OTHER end of those resistors were connected somewhere on there.

While it's out, try deoxiting the switch where you can see it.

Do you have a source for 47 ohm metal film 1/4 watt resistors?

if not, mouser.com:
660-MF1/4DC47R0F at a whopping $0.06 each... postage is gonna hurt...

 

[Noodle]

markthefixer,
Thank you too much.
Noodle

 

[Noodle]

Here's a question for all the techs.
What is the difference in a carbon film and a metal film resistor?
And just out of curiosity, why would a metal film resistor replace the carbon film resistor in this situation?
Thanks.

 

[markthefixer]

Here's a question for all the techs.
What is the difference in a carbon film and a metal film resistor?
And just out of curiosity, why would a metal film resistor replace the carbon film resistor in this situation?
Thanks.

Back then the prime factor was cost (might still be - in production quantities), metal film was more stable and quieter - a higher quality part.

I didn't notice on this model they only have a FEW metal film resistors specified on the board - in sensitive spots....

I didn't try to see what was available in carbon comp resistors, i just went straight to metal film resistors. I use them a lot.