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Yamaha C-70 issue

marloubow

marloubow

Best Day Ever
Hi Guys / Gals,
I have a Yamaha C-70 that I really like. At power up the right channel has a problem where it cuts in and out, sometimes abruptly and sometimes it fades in and out until it warms up, say, 5 to 10 min. then plays fine.

Anything obvious come to mind?

My test equipment is limited to a DMM.

Thanks

martin
 
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:lurk: a bright light, magnifying lens, and non-conductive probe will all be helpful in checking the circuit board, both component side and solder side.

Be careful though if you're trying to check while powered up - that could lead to problems or disaster depending on where you're poking around.
 
Thanks mech,
That's been my approach...nothing yet visually or that I can hear.
But, my probing "window" is only about 5 to 10 min at power up. After that the unit behaves properly and can't be made to misbehave.
Thanks guys for indulging me in this low-tech approach prior to another trip to a tech.

martin
 
Could also be a transistor misbehaving at start up until it thermally stabilizes.You can locate these with a can of freeze spray.By simply freezing the right side transistors one at a time and listen for drop outs.
 
Well guys and gals,
I found the problem by poking and prodding.
The C-70 has access to the boards thru the top and bottom. As I would turn the unit over or "twist" the chassis, the channel(s) would cut out (or clear up) and I was able to isolate the problem to this component.
I believe it's a relay...RY502. The contacts don't seem to be fully seperating until they warm up. I can push them apart and the channel clears up.

I've tried deoxit.

Can these be replaced or fixed?

Or perhaps there is a component in the circuit thats not doing it's job?

Any help is appreciated.

Casing markings...

MATSUSHITA
11 0 21 / 0.5A 125VAC
AW622226 1A 30VDC
HB2YD-DC24V

thanks

martin

DSCF0036.jpg
 
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I'm away from the unit at the moment...wonder if I can swap out one of the other relays? Maybe the mute relay?
thanks
martin
 
marloubow said:
I'm away from the unit at the moment...wonder if I can swap out one of the other relays? Maybe the mute relay?
thanks
martin
Click to expand...

What makes you think another relay from that set is in better shape?

I'd just wholesale change those with new, better ones. I don't think it'd be worth your time to desolder a potentially bad one and use it to replace a bad one.

If you want to confirm if a replacement would fix it, you can hardwire the contacts you want closed and see.

Note: do not have your power amp on during power up. A transient could make it through.
 
Jon,
From this info, can you tell which is the coil voltage?
MATSUSHITA
11 0 21 / 0.5A 125VAC
AW622226 1A 30VDC
HB2YD-DC24V

thanks for helping
martin
 
Hmmmm. It seems like that relay footprint has gone away and the old stock dealers are gouging people by charging %50~$65 bucks per relay.

What I would do.

I would take the relay out and find it's common connection as well as it's N.O. (Normally Open) and it's N.C. (Normally Closed) contacts as well as it's coil contacts. I'm guessing it is a DPDT (Double Pole, Double Throw) Or you can look at the schematic and board picture and get the info that way.

After the pinout is determined, I would buy small signal, DPDT (if that's what it is), relays and kluge them in. That means attaching extension wires to the leads and remapping the wires to get them into the appropriate holes. It's either that (if the pins don't line up), or solder it in (assuming the pins line up, then cutting the PCB traces and re-mapping underneath.

I don't like cutting traces and would rather re-map into the holes.



I can't find a datasheet for the HB2YD-DC24V, so it's difficult to select a sub.
 
Jon,
Thanks for the leg work!
I PM another AK'er who had a similar issue a couple years ago to see if he found a resolution. AK'er has answered and had no luck either.

I would agree to try your approach, except for the fact that the C-70 is far from mint condition.
One of the boards has lifted traces that I've had to jump. The hinges on the drop down face are non-existant.
The faulty relay is the Tone/Parametric relay and is most likely just flat worn out, due to constant switching between flat and the tone controls
by the previous owner(s).
So, if the "audio mute" relay will do, I'll try that. I just need to make sure that the mute is not engaged.

martin
 
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