NEED HELP! (...with Pioneer SX 770 receiver)

[thattreeguy]

Audiokarma thanks for reading and helping!

A week ago I posted a thread about completing my main system, which took a lot of time & money. It sounds awesome & I love it...yet I can't stop bringing home stray components...

My latest orphan is a lovely (on the outside!) looking Pioneer SX 770 receiver.

On the inside she was filthy...everything coated in a thick layer of nastiness and probably cig. smoke. I did my best to clean her up with a can of compressed air and CRC QD Electronic Cleaner. I didn't have any deoxit d5 ( my can stopped spraying...feels like there's about 1/4 of the can left but I can't get it out! bummer!!) so I used the CRC cleaner to clean & work the pots. I did use Deoxit d100 with the brush applicator on the RCA jacks & the weird speaker adaptors. I let it sit out for about 2 hrs, put her back together, connected a turntable & speakers and plugged her in...and it sounded awful.

The left channel sounded good damn good actually, the right channel not so much. It wouldn't come on at all until I turned the balance all the way to the right. Then it would play weak with no bass and distorted. When I turned the knob to about 3 o'clock the left channel would kick in and it almost sounded stereo but weak & like crap. Turning the balance all the way to the left would distort the left a little but not nearly as severe as the right channel.

After a couple hours of scratching my head and swapping out cables, speakers and components which it all sounded like crap until it dawned on me to turn the radio on (which I NEVER do because commercials rot your brain!)...

...and it sounded beautiful...balanced, full, bass for days & crystal clear. So good that I'm determined to fix her but am broke from main system. So must be DIY.

With my very limited experience & knowledge of electronics I am almost certain that the radio working signifies that it is a problem with the pre-amp. Also that it's not a problem with just the phono stage because same thing happens with CD in aux jacks. Is this an accurate diagnosis?

Is there anyone reading who has experience with the SX 770? Could this be a common issue with this model? Where do I begin? Possible causes? I am electronically challenged but wanting to learn...when I look inside her (pls. see pics) I have no idea what I'm looking at other than the pots. I don't even know what the pre-amp section looks like or where it's located...

I did download the manual & looked at it but it didn't make a lot of sense to me.

So ANY help or info (dumbed down please) would be GREATLY APPRECIATED!

 

[fill35u]

The left channel sounded good damn good actually, the right channel not so much. It wouldn't come on at all until I turned the balance all the way to the right. Then it would play weak with no bass and distorted. When I turned the knob to about 3 o'clock the left channel would kick in and it almost sounded stereo but weak & like crap. Turning the balance all the way to the left would distort the left a little but not nearly as severe as the right channel.

After a couple hours of scratching my head and swapping out cables, speakers and components which it all sounded like crap until it dawned on me to turn the radio on (which I NEVER do because commercials rot your brain!)...

...and it sounded beautiful...balanced, full, bass for days & crystal clear. So good that I'm determined to fix her but am broke from main system. So must be DIY.

Those symptoms seem strange to me, since past the Tape Monitor switch, the signal path is identical for all sources. They all go through the Stereo/Mono switch, the Loudness control, the Volume pot, the Control Amplifier, the High Cut control, the Balance pot, the Main Amplifier, and the Output Selector. So a problem in any of those should affect *all* sources the same.

Maybe there's a problem on the *ground* side of the signal? Perhaps by twisting knobs you're disturbing a loose connection just enough to change it? I'd use a meter to verify continuity to signal ground at all the RCA outer shells for all the inputs. Then I'd trace that signal ground back and verify continuity all the way up to the Main Amp board. It may be something as simple as a loose wire, loose screw, or corrosion under a screw where it goes through a circuit board.

 

[thattreeguy]

Thank you fill35u for the response and the info. Sounds like my diagnosis was inaccurate because the tuner signal travels the same path. I don't know anything but I'm trying to learn. Is it possible that it is the RCA jacks that are faulty? I guess this could account for why the radio sounded good and components plugged into phono and aux jacks did not?? The phono jacks seem kinda of loose from the back outside of the receiver but not the aux ones. Also it's the same channel that's affected for both inputs. Seems odd to me that both sets of inputs have the same faulty one, but I guess it's possible. Is there a wire or connection that would affect all the RCA inputs? I suspected something might be awry with the input jacks that's why I tried to show them from the inside in pic 6, but like I said I don't know what I'm looking at.

I'm going to obtain a meter and check for continuity like you recommended, but I have no idea how to do that. Maybe you could give me a brief synopsis on how to do that or direct me to a good tutorial?

Thank you so much for your help!

 

[fill35u]

I'm going to obtain a meter and check for continuity like you recommended, but I have no idea how to do that. Maybe you could give me a brief synopsis on how to do that or direct me to a good tutorial?

Thank you so much for your help!

You're welcome!

I'm not familiar with this receiver or how Pioneer did things. I think at this point you'd get better help if you asked in the "Pioneer" forum of this site, maybe you could ask a moderator to move this thread there.

 

[Jauk]

It's possible to diagnose even without knowing much if you're able to follow the signal path, but BUT CAREFULL with electricity!!! I don't know that much but I would say by the symptoms it's probably the selector switch that needs to be better "Deoxited". I suggest getting a can of Deoxit and redoing all the cleaning, specially the input selector. Be sure to act on the switches a lot when doing it, clean the mess after you're done and let it dry out before turning it on, maybe help with a hair dryer... BTW the cleaner must get inside the switches, sometimes it seems like it does but it doesn't.
Also, are you sure 2 hours is enough ? Make sure it's dry... Some cleaners (I don't know about that one) are conductive!

 

[merlynski]

After looking at the schematic and your pictures I, as well, suspect the Selector switch S1 has dirty/corroded contacts. It needs close attention to cleaning and Deoxit. If your can of D5 lost its pressure poke a couple of holes in it and drain the D5 into a small bottle and use it like you did the D100. The D5 has solvents, the D100 does not. For cleaning the D5 is probably better. Exercise the switch repeatedly, to help break through surface corrosion, while it is wet with D5.

 

[EastPoint]

If FM is fine and other inputs are not, it’s probably dirty controls, specifically the source selector switch.

 

[thattreeguy]

THANK YOU fill35u, Jauk, merlynski, and EastPoint! You people are super cool!

I got a new can of the D5. Cleaned the SX770 all over again, paying particular attention to the source selector and waited about 6 hours. Problem solved! Right now it's connected to a Sansui FR-5080 TT with a Shure M91ED cart. and some old (~1990) PSB 50MKII speakers. It is a lovely clear warm sound and I'm diggin' it.

I really do appreciate it.

ANALOG IS KING!

Buddha likes it.