Yamaha C-50 Preamp - NEED HELP - strange problem

[Dolphins]

My Yamaha C-50 has a strange problem when recording from phono. When I set the "REC OUT" switch to phono, I am only getting sound in one channel. This switch is to select the source that you want to record from. All other sources are fine.

I have checked everything else - connections, different decks, tape 1 and 2, phono 1 and 2. It is definitely an internal problem in the preamp. It seems like something in the internal circuit from the phono to the tape loops. I have already cleaned the relays and the switch that controls the (rec out). It is possible that further cleaning will be required.

Does anyone have any suggestions on where to start?

 

[brutal]

Did you use DeoxIt (recommended) or something like a tuner cleaner from Radio Shack (not recommended)

You did swap the L/R channels to be sure it's the pre?

 

[Dolphins]

Thanks - yes used Deoxit. Just sprayed it again & will let it soak overnight.

Definitely not the connections. Everything works fine on all sources during normal playing. It is only when recording from either phono input, and only on one channel. When I switched L/R I got sound from the other channel. But still only one channel at a time.

I have tried both my RtR deck and CD recorder - same thing. The meters on both are indicating in input signal on only one channel.

It is something inside the preamp that causes the phono to only work on one channel when recording.

 

[brutal]

Thanks - yes used Deoxit. Just sprayed it again & will let it soak overnight.

Definitely not the connections. Everything works fine on all sources during normal playing. It is only when recording from either phono input, and only on one channel. When I switched L/R I got sound from the other channel. But still only one channel at a time.

I have tried both my RtR deck and CD recorder - same thing. The meters on both are indicating in input signal on only one channel.

It is something inside the preamp that causes the phono to only work on one channel when recording.

Are you rotating the switch positions for a minute or so after spraying in the pot/slider? Not certain on the C-50, but most of those Yami pre's have a flat metal ribbon cable that goes from the front panel selector to a slider switch in the rear of the unit for many functions, particularly the rec-out.

 

[ryuuoh]

My experience with my C-50 was it had many cracked solder joints. I fixed them all, and it runs perfect. Still waiting for the relay issues!

 

[Dolphins]

Yes, I rotated the selector switch. And yes, you are right about the ribbon type cable. I sprayed the switch at the end of the cable. I am wondering if this this is a single or double switch ie. is there a single contact inside for phono, etc or a double contact for L/R?

I know the relay switches inside these preamps (and other Yamaha models) are problematic. Do you know if the REC OUT is controlled by one of them?

 

[brutal]

Yes, I rotated the selector switch. And yes, you are right about the ribbon type cable. I sprayed the switch at the end of the cable. I am wondering if this this is a single or double switch ie. is there a single contact inside for phono, etc or a double contact for L/R?

I know the relay switches inside these preamps (and other Yamaha models) are problematic. Do you know if the REC OUT is controlled by one of them?

Do not know, have you checked for a schematic or SM in the AK Yamaha database? IDNK if the C-50 even used relays? [EDIT] I see the C-50 has a relay bank just like the C-70...

I expect the slider would have L/R pads. Do you have any faderlube you can try? If the pads are carbon over plastic DeoxIt D5 (with solvents) can harm the carbon coated plastic. I've only got C-60 on up here as reference.

Any chance the solder joints on the bottom side of the slider need attention? Those plastic sided pre's can flex and develop cracked solder joints from flex and heat/cool cycles.

 

[avionic]

My experience with my C-50 was it had many cracked solder joints. I fixed them all, and it runs perfect. Still waiting for the relay issues!

Most probable problem.Look at all then PCB solder connections for the phono select switch--SW1-1,3

 

[Dolphins]

Thanks for your help guys, but so far no luck. I re-soldered both switches SW101 & SW103. No change

 

[Dolphins]

I AM A HAPPY CAMPER!! It is working perfectly now (shhh... I had one tape in/out mixed up). I did have it hooked up correctly before, because all other sources worked fine.

The problem was either a dirty switch (SW103) that may have benefited from an overnight soaking, or bad connection at SW101 or 103. I am leaning towards a bad solder joint.

While we are on the topic, what preamp in the yamaha line would be considered an upgrade over the C-50? Phono stage is most important to me. I replaced my Parasound P/HP-850 with this C-50. The phono stage in particular was much more musical, dynamic and lively - quieter too.

I currently have it connected to a pair of JBL 6230 monoblocks (awesome, undervalued amps), a Dual 1229 turntable, Ampex ATR-700 Reel to reel, and Sound Dynamics Concert Monitor 1500 speakers. At 102 dB efficiency, the 150 watt JBL's can put out some serious sound pressure. They blow away a Luxman M-02 amp.

This problem with the Yamaha was a big deal for me. Not only for the recording, but I like to run my turntable through the Ampex preamp section and listen through the tape monitor. This puts the TT volume on par with a CD player.

Again, thanks very much, from Canada to the fellow members who quickly helped me fix the Yamaha.

 

[brutal]

Upgrade?

C-70 in the same family,

C-2a or C-2x for uber Yami pre.

 

[Dolphins]

Just thought I would post an update - after thinking everything was alright, the same problem re-appeared this morning. I turned the unit on/off 3 times and voila - worked perfectly. It seems now like dirty / bad relay switches.

 

[avionic]

If it is a relay there is no cleaning...Replacement only .:yes: They use little sealed reed switch relays..like the ones in the photo. Actually the problem still sounds like either a bad solder connection or a heat sensitive transistor.

 

[dkelley]

Did you use DeoxIt (recommended) or something like a tuner cleaner from Radio Shack (not recommended)

You did swap the L/R channels to be sure it's the pre?

What's not recommended about RS tuner lubricant? Assuming you mean the tuner lubricant and not the contact cleaner. contact clear is a no no. tuner lubricant is brilliant stuff as long as you know how to use it and what it's actually better for than something like deoxit. the switches in the c-series control amps slide along long shafts. Radio shack tuner lubricant is actually the stuff you want for it. Works AMAZINGLY well and is my preferred stuff for exactly this situation (and worked wonders on my otherwise DOA c-70 when I got it). also the preferred stuff for potentiometer cleaning imho. deoxit removes oxidation more than anythign else, although it does a good job of cleaning as well. tuner lubricant (whether radio shack or whatever) does things differently.

the only caveat is that using tuner lube you have to operate the pot or switch or relay repeatedly until the lube dries so it doesn't just make things worse. if you do that it will almost always fix things to perfection.

cheers,
Don