SX 980 - no sound in the right channel in stereo mode when using tuner

Hi guys, I am having an issue with no sound out of the right channel when using the tuner in stereo mode. When I switch to mono I get sound. I thought it was the mode switch itself so I desoldered it took it apart cleaned the contacts and reinstalled it and it is doing the same thing. And yes I did deox everything before hand with no luck..... What's the next step? It has no other problems in both channels in stereo on any of the other functions.

Thanks,
Jeff

It might be worth doing a quick test as follows: If you can locate pins 19 and 21 on the tuner circuit board (which are the L and R outputs, respectively, of the FM tuner), just short those two pins together. If you then get sound from both channels, you know the problem is on the tuner circuit board.

(There's no risk of harming anything by shorting the output pins to each other. You'll want to be careful not to connect them to anything else, of course.)

Assuming the problem IS on the tuner board, my guess would be the low pass filter, but it's not so easy to come up with a home-brew test to confirm that.

Good luck,

chazix

I just downloaded the manual. I will perform that test and check back in a bit. Thanks.

Yes, I do get sound when I jump pins 19 and 21 in both channels. So I am assuming the problem is on the tuner board.... From what I can see nothing looks burnt or leaking. What's next?

OK, I'm over being mad at AK for eating a post, and will replace my rant with more or less what was eaten. I'll save a copy BEFORE hitting save, that's for sure!

My next suggestions are somewhat riskier in that they will involve shorting together L & R signal points in the interior of the tuner board. It's still completely safe as long as all goes well, it's just easier to make a slip when working in the interior.

First, short together the terminals of R46 and R47 that are nearest to the low-pass filter (F4, a large-ish rectangular block). These are the output points of the LPF, so if you now get sound in both channels, it means the problem is in the LPF or before it. If you DON'T get sound in both channels at this point, don't proceed with the next suggestion.

Next, short together the terminals of R33 and R34 that are nearest to Q6, the PA1001 chip. These are the input points of the LPF, so if you now get sound in both channels, the problem is before the LPF, perhaps something wrong with the PA1001. My hunch is that you'll only get sound in one channel at this step, which would tell us that the LPF is bad. That would not be good news, since I'm not sure how you could fix that, but better to know than not know.

chazix

Thanks, I will try the suggestion and report back

Hello chuck,
I didn't get sound in both channels when I shorted R46 and R47 together... What's next lol?

An update for those who are waiting with bated breath to see where this goes: Jeff found that shorting the outputs of the low-pass-filter did NOT result in both channels sounding.

So, the problem is somewhere between the LPF and the output terminals of the circuit board. I suggested checking the DC voltages on the PA1002 chip, which seems to be an audio buffer with a muting control. (In other words, I was stalling for time, having no clue beforehand what a PA1002 might be...)

The inputs of the PA1002 are pins 3 and 14. The outputs are pins 5 and 12. That info might help to further the diagnosis (or at least might help someone else who happens upon this thread).

I really appreciate the help Chazix! After probing the voltages on the chip, it was found to be bad on the pins 5 and 12. After some reading it seems this chip is unobtainium. I read the link above, did this guy ever finish the replacement chip? Did it get marks blessing? Is there another source for these?
Thanks,
Jeff