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Yamaha R-50

H

Hamm

New Member
Hi gang...

I joined this forum as a starting point to fixing my Yam R-50 receiver. Had it for many years and it's always worked like a champ, till now.
I was playing a tape, pretty loud, and suddenly it quit. Found that it had blown the fuse. Replaced fuse, but no sound now. Lights now come on and things look normal, but no sound at all. Any advice on how to start tracking down the issue?

Hamm
 
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Welcome aboard. I notified the moderators about putting this in the Yamaha section. You'll get more attention there.
 
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3-5 seconds after power on do you hear a faint click of the protection relay. No click indicates amp may be in protection mode or...
 
I hear no click but it takes about 3-4 secs for the "signal" meter to light up each time.

PS: I got the manual. Thanks.
 
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Found a suggestion on another thread that STK-4873 may be blown. I found that component in the manual. I'll get the thing out of the cabinet and crack it open tomorrow. Thanks. Don't really have much electronic experience or test equipment, but I have fixed lots of things in my life. I'll take a shot at this.

PS: I see that people are replacing capacitors in older units like this. That's not very hard. Maybe I'll do that too.
 
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If you do hear a click as per @mbz , then it’d be time to look under cover and look for any damages. I noticed there are a couple of hard to find ICs in this unit (IC112, IC111) STK4873 and M5219L respectively. FWIW, I hope you don’t hear a click and that the issue is not one of these ICs.
 
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No click. I'll make room on my workbench and open the thing tomorrow. I make jewelry and the bench is covered with new stones I'm cutting right now.
 
Be aware that the R-50 uses a heat pipe to cool the STK and loss of heat pipe cooling effectiveness with age can contribute to failure of the STK (if that is your problem). This should be considered before you try slapping in a replacement STK.
 
Thanks for that suggestion. Never heard of a "heat pipe" before, but I looked it up. Not sure how you can know if one is not working well, but I'll keep it in mind.
 
To confirm the amp is in protection, ie, not a protection circuit fault, measure dc voltage at either end of R345, marked in red below, repeat for R346. Black meter probe connected to chassis/GND. Anything over a few hundred mV would indicate protection fault.
 

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OK... it's open. I'm seeing obvious heat discoloration on the inside of the top cover over the transformer and also about 4" to the right and just south of what is labelled the "diode bridge" in the manual photo. That component is mounted to a heat sink and is marked "D635". There also seems to be some faint darkening on the back of the circuit board under that heat sink. Some obvious leakage is seen under the two capacitors just to the right of the transformer. They clearly are failed/failing.

There is no heat signature seen over the STK, and the "heat tube" assembly looks pristine.

I have not yet attempted the testing suggested just above.

Clearly, I need to replace those two caps, but could they have caused my current condition?
 
Hamm said:
OK... it's open. I'm seeing obvious heat discoloration on the inside of the top cover over the transformer and also about 4" to the right and just south of what is labelled the "diode bridge" in the manual photo. That component is mounted to a heat sink and is marked "D635". There also seems to be some faint darkening on the back of the circuit board under that heat sink. Some obvious leakage is seen under the two capacitors just to the right of the transformer. They clearly are failed/failing.

There is no heat signature seen over the STK, and the "heat tube" assembly looks pristine.

I have not yet attempted the testing suggested just above.

Clearly, I need to replace those two caps, but could they have caused my current condition?
Click to expand...
Some pictures would help. The caps could be leaking, or that could be assembly glue.
 
I'm not seeing numbering on the resistors and your diagram is too small for me to figure out general location. What portion of the board are you indicating?
 
Is that something you put on the circuit board around those big electrolytic's ? Like alcohol ?
 
Hamm said:
I'm not seeing numbering on the resistors and your diagram is too small for me to figure out general location. What portion of the board are you indicating?
Click to expand...
The speaker relay (RY101) and the STK were included to help you locate the items. They will be next to inductors, copper coiled wire typically in a plastic wrap.
 
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