Yamaha C4 loses volume in 1 channel

[Mat86]

So I recently attempted restoring a C4 and noticed this issue out the box, I was sometimes getting no volume on AUX, or just 1 channel, but switching to Tuner solved it so I assumed it was an Aux input issue or dirty contacts

during the recap I did a test half way through and had volume in both channels and pre-out to another amp was seemingly fine. When I was done it was working as well.

Left it to burn in over night and a few hours later listened and noticed the left channel was out and the sound itself was muted (as in, off, dampened). Tried Tuner and it was fine, so back where I started at least.

...then the Tuner input went on me. I noticed that jiggling the switch between Aux and Tuner would get the left channel going again, but it wasn't consistent. I then noticed that rebooting the system was 100% consistent in restoring the volume in both channels.

Fast forward, but I now tried the Phono stage and it did the same crap, but toggling the Phono knob (its a different knob than the input one) got it going extremely temporarily (like mid rotation)

So here I am:

• Various channels lose 95% of volume (not all, its just quiet as hell)
• Affects multiple inputs
• Power cycling fixes the Tuner input, but not Phono
• Seemingly not an output issue, since the headphone amp is n different from pre-out, and mono outputs both channels while stereo/reverse alternates the signals fine
• Yes, I've blasted the ever living crap out of the switches with cleaner

What do I do?

 

[avionic]

Disassemble and clean the switches and controls. Check the solder connections on all TO-220 transistors in the power supply.Check your solder connections for the various switches and controls.

 

[Mat86]

Disassemble and clean the switches and controls. Check the solder connections on all TO-220 transistors in the power supply.Check your solder connections for the various switches and controls.

I don't believe the power board has TO-220s?

 

[avionic]

Thats not the entire power board. There are three TO-220 with heatsinks on them...At the other side of the unit.They are for the regulated power supply and the relay driver..

 

[Mat86]

Thats not the entire power board. There are three TO-220 with heatsinks on them...At the other side of the unit.They are for the regulated power supply and the relay driver..

Technically the manual calls that board the "Flat Amp" but yeah, see them, thanks I'll take a closer look at those

 

[avionic]

The function switch may very well have bent contact springs or loose rivets...Springs can very carefully be bent back into position. <------- extremely easy to break .. Some have had good luck with soldering the rivets. Wiggling the wafers will give you and indication as to the wellness of the switch.

 

[Mat86]

The function switch may very well have bent contact springs or loose rivets...Springs can very carefully be bent back into position. <------- extremely easy to break .. Some have had good luck with soldering the rivets. Wiggling the wafers will give you and indication as to the wellness of the switch.

Does a physically damaged switch jibe with the symptom of being able to alleviate it by power cycling? When I do that, or reseat the RCA cables, I can toggle the switch to my heart's content (until it craps out again at random, hours later)

 

[avionic]

It sounds like a bad connection.. ie dirty switch ,solder connections,............relay contacts... I've only probably repaired or refurb'd 20-25 of these in the past few years. So I know there weak points.. RCA solder connections .. Ground solder connections...Reed relays with intermittent contacts...dirty or broken wafer switches.. dirty slide switches , that can only be cleaned by dissassembly... Bad solder connections on the ribbon cables....

 

[avionic]

Next time it craps out.. Tap on the little metal cased reed relays. There are three of them.. Instead of the RCA's or the power button.

 

[Mat86]

It sounds like a bad connection.. ie dirty switch ,solder connections,............relay contacts... I've only probably repaired or refurb'd 20-25 of these in the past few years. So I know there weak points.. RCA solder connections .. Ground solder connections...Reed relays with intermittent contacts...dirty or broken wafer switches.. dirty slide switches , that can only be cleaned by dissassembly... Bad solder connections on the ribbon cables....

hah I can tell, saw an old thread with a similar sounding issue and you were in the thick of it there as well (and thank you for helping). With so many possibilities though, trying to narrow down where to start in this haystack.

Next time it craps out.. Tap on the little metal cased reed relays. There are three of them.. Instead of the RCA's or the power button.

These suckers? I see two / listed in the service guide, there anything else worth tapping on?

 

[Mat86]

Next time it craps out.. Tap on the little metal cased reed relays. There are three of them.. Instead of the RCA's or the power button.

good(ish?) news. After about 24 hours of no self-induced problems, the problem happened so I started tap dancing for ideas. Nothing on the relays but decided to give the switch a little nudge per your advice in the old thread and bingo.

2014 thread advice:

From my research, the switches can be signal traps.

Have you thouroughly deoxit'd the Input Select and the Phono Select wafer switches ? While listening to the pre-amp with a TT . Listen for the left channel phono to cut in and out while gentily flexing the individual wafers of both the wafer switches previously mentioned.

Both popped back in full, and a little more feeling had it in and out until both were out and my panic set in. Little deoxit therapy and finger crossing and it's currently back so not touching it again just yet. What next, pulling it out? Reflowing solder? Walk away?

 

[Sparkplug]

I’d reflow all the solder joints on all of them switches. Their leads are usually many and small so it’s hard to see solder cracks if there are any, best to retouch them all.

 

[Mat86]

I’d reflow all the solder joints on all of them switches. Their leads are usually many and small so it’s hard to see solder cracks if there are any, best to retouch them all.

frustratingly I reflowed them all and it didnt impact things, so back to poking around. All I've found is that putting some pressure on the inner wafer of that switch gets channels moving again, though I also noticed the Phono channel went into pure buzzing when I did this (edit: buzzing was amplified when my hand was near the circuit board and neutralized when i touched the chassis with my other hand; this was with the case off)

 

[avionic]

The function switch may very well have bent contact springs or loose rivets...Springs can very carefully be bent back into position. <------- extremely easy to break .. Some have had good luck with soldering the rivets. Wiggling the wafers will give you and indication as to the wellness of the switch.

 

[Sparkplug]

frustratingly I reflowed them all and it didnt impact things, so back to poking around. All I've found is that putting some pressure on the inner wafer of that switch gets channels moving again, though I also noticed the Phono channel went into pure buzzing when I did this (edit: buzzing was amplified when my hand was near the circuit board and neutralized when i touched the chassis with my other hand; this was with the case off)

This was not a wasted effort, had to do it anyway, no way around it. The cause could be any number of physical failures. Your best bet, follow what avionic is suggesting to the letter. If that didn’t work (unlikely), then other remedies can be considered.

 

[Mat86]

Just want to prep before disassembling anything so I don't break anything, found these threads on people fixing these (since someone else will inevitably find this thread someday too) but not much in terms of pics

Yamaha C-4 input selector switch repair | Audiokarma Home Audio Stereo Discussion Forums
C 4 selector switches | Audiokarma Home Audio Stereo Discussion Forums
C-4 Input Selector Switch | Audiokarma Home Audio Stereo Discussion Forums

pic from 1st thread:

What order do I remove or de-solder things? There's the wafers, the metal housing, and does the shaft come off?

Which are the 'rivets' that may need to be soldered in place - the circular parts? Does anything in here need to be re-lubricated after cleaning?

 

[avionic]

What order do I remove or de-solder things? There's the wafers, the metal housing, and does the shaft come off?

Unsolder both the housing pins and both wafers before trying to remove it from the circuit board. You will then be able to slide the wafers off the shaft.