Yamaha CR-800 Receiver - Weak Right Channel Output

[Haileyburian]

I’ve been working on a Yamaha CR-800 off and on now for the past few weeks. The unit was covered in dust and what likely was a nicotine film. Cosmetics now are excellent. Seems the dust/dirt acted as a bit of a shield from worse harm. Service Manual is here on AK.

ISSUE:
The Left channel is great on both Speaker and Headphone outputs, with FM and Auxiliary (CD player) inputs.
Right channel output is present, but very limited. On FM, Right channel output is stronger in Mono mode than in Stereo, but still noticeably weaker than the Left. On Auxiliary (CD), Right channel output is stronger than in FM but still very weak. The Right channel is steady at the reduced volume and does not come-and-go.

WHAT I’VE DONE:
- Did an AK Google search but could not find anything helpful
- DC Offset at speaker terminals, after adjustment = 0.001V, both Left and Right
- Idling current after adjustment is right at spec for both channels, 0.023V
- DeoxIT’d all switches and pots at least twice, concentrating on the Balance/ Volume control and the Audio Muting switch on the Front panel, and the Pre Out/ Main In Coupler switch on the Rear panel
- With the Coupler switch ‘Off’, ran a patch cord from the Pre-Out Jacks to the Main In jacks. Result = Right channel still very much weaker than the Left. Swapped Left and Right at Main In jacks, and the problem switched – the Left channel then became the weak channel

Apparently “someone” was in there before, as the meter lights are wired weird – wires from 2 lamps are soldered to 1 wire which is soldered to terminal. Might this have any possible bearing on the Output Imbalance issue?

Any suggestions where/what else to check…?

 

[Haileyburian]

Suggestions? Advice? Thoughts? Opinions...?

Barry

 

[terra1]

I am not a tech but until one comes along ...

After deoxiting, did the weak channel improve? If so then I may deoxit some more. My CR-800 had weak intermittent right channel until I deoxited it after taking it out from about 20 year storage. Had to deoxit it a few times.

I usually clean front, internal boards and contacts, rear connections on inside and out. I have found it may not just be the usual spots that can affect sound. I have found selector switches, tape monitor, and others can affect stereo and balance. Good comprehensive tutorial: http://www.audiokarma.org/forums/showthread.php?t=207005

If deoxit doesn't improve volume, I might check for any burned or cracked solder or check for loose wires, nudge some wires with a chop stick to see if it affects sound.

Could be some failing part, which again, hopefully a tech can offer some advice. The fact someone got in there and did some rewiring makes me nervous they may have rewired something else wrong. You may want to take some photos.

 

[merrylander]

It sounds like the power amps are fine since the problem switched channels in the open coupler/interconnect test.

On either side you can see two large screws with red heads - remove them and loosen the two large screws with gold heads.

Unplug the yellow wire that goes to the tuning head, it unplugs right at the head. Also unplug the red and green wires - the plug is right at the antenna connector.

Good, now you can pull the whole front section forward and tip it downward. Now you can get a real good shot at the input selector switch and really get some Deoxit into it.

 

[Haileyburian]

terra1 - No, channel stayed at same weak strength after DeoxIT/FaderLube treatment. Signal strength is even, not intermittent, just at much-reduced volume. As yours, this unit apparently had sat unused/in storage for 7+ years. I'll poke around a bit more with my chopstick.

merrylander - So you're thinking the Input Selector switch might be the culprit? I did drop the front section forward and down (a terrific piece of industrial engineering:thmbsp and blasted all front panel switches and controls, but I'll go back at it again.

If no improvement after this round of DeoxIT/FaderLube, think I'll take a break from it for awhile, let everything 'sink in', and come back at in a week or two. There's just too dang much else to do...!

 

[ryuuoh]

I find this to a great help when looking for bad connections/solder joints.

 

[ecluser]

As Merrylander said, the problem is before the power amplifier section.

The question is: is it before the selector switch or after this switch?

Can you check the signal from the tape out jacks? This will confirm if the tuner section is good.

 

[Haileyburian]

Thank you ecluser. All thoughts, advice, hints, etc greatly appreciated. Unit really is a lovely piece of design/industrial engineering and I sure don't want to see it scrapped.
Thinking out loud a bit here - I don't think that the tuner is the problem area, as issue is similar on both FM and Aux inputs. I'll try AM (not even sure if we have AM station locally:scratch2 and Tape outputs later this evening...

 

[merrylander]

It just occured to me that you could have a bad solder joint at the coupler switch area. Note that the back tips out just like the front.

 

[DragonMaster]

If you have a 'scope (or a multimeter on 2V AC would do), send a sine wave from a CD player, disconnect the power amps by turning off the coupler switch, and turn up the volume. You'll be able to compare the signal level at various points in the signal chain. When the levels start to mismatch, you then know where to look. Check for cold solder joints, etc. Check the resistance between each channels to ground. Maybe the right channel is almost shorted to ground?

 

[Haileyburian]

A little context - I'm great at clean-up, both cosmetic and DeoxIT/Faderlube, good at visual (bad connections, cold/bad solder joints, etc; that link looks mighty handy ryuuoh) and moderate solder/un-solder skills. Much beyond that and I'm looking for a good technician with decent vintage experience, unless the good and learned folk here can lead me step by plodding step
Away for a bit, then will take another crack at it...

 

[ecluser]

Of all the switches, the input selector switch is, by far, the most solicited switch in this receiver. Right?

Repeated action of the input selector switch may break the solder joints between the switch and the board. Without a magnifier, this may be difficult to see.

You should remove the old solder and put new solder for each terminal of the input selector switch, then reevaluate. This is my suggestion, at this point.