Swapping Circuit Board

[Oldsansui441]

Don't let it get you down, we have all had units that have frustrated us to the point of wanting to hoist it over the neighbors fence. I suspect if you are reading voltages on the solder/trace side of the board and not the component side that the component legs are a little corroded or have a build up on them not allowing you to get a good contact with your test leads.

 

[biggal76]

Yes, I guess that could explain why I'm getting voltage from the component side but I'm not getting it to the ICs even on the solder/trace side.

 

[Oldsansui441]

Oh l see, you aren't even getting it to the solder side of the IC's, hmm very strange.

 

[rcs16]

I got power to L1 and R6 but when I measure to pins on Q7, no voltage. I don't understand how the power can be interrupted in between components when one thing has voltage exiting it and the next doesn't have it entering. I also got voltage from the bottom side of the board on the solder joints but not from the top which makes 0 sense to me.

It has to be that our probe has not made good contact to the pin. These pins oxidize, so you have to press hard on the pin for the pointy probe to break through the oxide.
I understand that it gets frustrating, even for me sometimes when things get confusing. Sorry we could not figure it out for you. If you need further assistance, reply to this thread, I am monitoring it. If it gets fixed, let us know so we know what the problem was and others are informed of the fix. It seems that the SX-x80 series have more tuner problems than the x50 series. All they changed was a few IC's to their branded types vs the Hitachi standard types.

 

[biggal76]

I was pushing pretty hard and kind of scraped around on the solder joint a little with the probe, but it is a cheap multimeter (with cheap probes). I have another i could give a try but I'm not optimistic it will help.
I'll follow up as suggested. Thank you for your help.

 

[biggal76]

Bided my time and got another tuner board on Ebay. I guess the first board I bought was dead. It seems to work well now. How frustrating to get a bad board and waste a year and a half and all this frustration. Hopefully it's all sorted out but I am having one problem. The stereo light stays on even if I switch it to mono with the stereo/mono switch. While tuning between stations on FM, the light goes off and on as it should but the stereo/mono switch does not seem to turn it to mono when it's already tuned in stereo. Any idea where the culprit could be? This has been a 3 year project so far, but I think I'm near the end of it.

 

[petehall347]

does it still sound stereo when switched to mono ?

 

[biggal76]

I initially said light stays on in other inputs but think I was mistaken. I edited my last post. Yes, the switch works from mono to stereo in other inputs so I guess I'm just having an FM issue. Or is the light supposed to stay on even if you switch to mono to indicate that it's tuned to a stereo station? Maybe it's working correctly?

 

[petehall347]

yes maybe it still says stereo when switched to mono . it sort of depends if fm stereo button is pressed .
hold on i need to look at one .

 

[petehall347]

ok from the manual i have doesn't mention fm mono button .so i would expect the light to stay on and sound to have left and right mixed producing mono sound when switched to mono .

 

[biggal76]

Awesome, so I guess I'm back in business. Will have to move it to the living room for a while and give it an extended listen on good speakers. Thanks for checking that out for me.

 

[rcs16]

yes time does pass rather quickly esp when you are looking for used tuner pcbs and have no easy way to test if they are any good or not.
I am glad to hear that you found a working tuner board finally and got it working properly again, good job. PITA for sure. tuners are difficult to fix even with the test equipment and knowledge. I am messing with a sx-1980 tuner now, it is finicky.
keep the other 2 tuner boards for parts. would be nice to sort thu them to find good/bad parts. need a test setup to do it easily, I have one that I use for sx-950/1050 tuners and have those as spares. if you wanting to get rid of them PM me, I should be able to sort thru and figure what is wrong, still a challenge.
Pete is correct on mono/st operation in done in the pre-amp section with a switch shorting L/R thru a resistor. stereo/mono switching is done automatically in the stereo decoder, PA1001-A, based on the 19KHz pilot level in the composite signal from he detector PA3001-A

Enjoy
Rick

 

[Oldsansui441]

Nice work biggal76 on getting your tuner up and running again.

so i would expect the light to stay on and sound to have left and right mixed producing mono sound when switched to mono .

Pete is 100% correct, l know it is a much lower end receiver from the line before but l have just finished a little SX-550 that does this also (mono button cancels stereo sound but not the stereo light).