Our faithful, 20 year-old Yamaha R-50 recently failed to power on. After checking things like the power cord and outlet, I carefully removed the cover and found a blown slow-blow fuse close to the the power transformer. I replaced this 250v 4a fuse and now the receiver will power up (lights on the console are lit). However, I am still getting no output to either the speakers or headphones, from either the radio or aux (CD) sources. Is there anything else that a careful novice like me can try or check, or is our receiver a lost cause?
Be careful with Google - since Yamaha also made an R-50 helicopter :-)
I never view equipment as a "lost cause" unless extensive damage has occurred (e.g. lightning) to a large number of components.
The Yamaha R-50 service manual is available.
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My troubleshooting regime starts with the power system. Is it functioning properly (proper voltages, etc.). Since you replaced the fuse and you are getting power to some devices (lights) - this would lead to in the following direction.
BTW all of this work if performed with the receiver unplugged from AC mains !!
Check rectifier (bridge or full wave design). Verify voltages correct (service manual helpful here).
Go to Power amplifier stage. I am not familiar with this model, but for this era - 2N3055 NPN transistors were not uncommon. Take out of circuit and test each -- as well as any ballast resistors.
T'hanks very much, gb! I had no idea that Yamaha was so diversified! Your suggestions are already over my head, but it is reassuring to hear that "lost cause" may be premature. I'm thinking that my next step will be to carry your suggestions with me when I take this unit into a repair shop.
The R-50 used an output IC which is no longer available from Yamaha or generic parts distributors. I forget the STK or IG number on the chip. If there's a DC output on one channel and the protect circuit is not firing the relay, you're probably out of luck on this one.
thanks for that - since I did not have a schematic. Loss of the IC is one possible scenario - but not the only one - you really don't know --- no one knows until actual diagnose. (can't start behaving like the medical doctors - "He's dead - Jim"!)
Well since you have a schematic now, I would grab my multimeter and start checking output voltages of the tranformer(s). Some have multiple windings, you may be getting 28v for panel lights etc. but no power to any of the other circuits.
When the (no longer available) output IC is confirmed bad, I'll expect acknowledgement. I've worked on enough of these to know, and that's my prediction.
I don't recall if this one had multiple windings at all, but I can't recall ever having a transformer fail in one of these. Nearly every one was output ICs. Been a while since we have seen any.
Besides, those old recivers with the single and two digit R- numbers, and basically anything that used integrated outputs were some of the worst stuff that Yamaha ever made. Not bad and even reasonably reliable if not pushed hard or into a low impedance load, but they were never up to par with the early units nor the stuff that followed. No reason to get teary-eyed about retiring this one.
I'm sure you will get all the accolades you can handle. :)
But, suppose he does find it to be bad? Is it so specialized that something can't be subbed with some modification?
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A lot of effort for not much receiver....and it would require all the documentation on the original chip, proposed subs, also engineering notes if circuit capacitors or other components needed to be added or deleted. Then of course there are mechanical mounting considerations.
So he should save the knobs and heatsink, and give the remains a nice burial. :)
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Yipes! I turned away from this thread for a couple days and now see that it's grabbed your interest! Many thanks for all for your suggestions. Everything you have suggested (except for the nice burial) is well beyond my capabilities. I'm just resisting the patriotic tendency to treat this receiver like a disposable consumer good. I'll carry your suggestions with me to a repair shop and hope for the best. Again, thanks to all for your assistance!
Still, if he was so inclined, really all he's looking for is signal in/out and B+/-. Then it's a matter of scabbing a chip amp onto the heat sync along with a small pc board containing its associated components.
you most likely have bad Caps in the power supply.. a lot of receivers have power supplies that sample the voltage at the main caps while they are being charged via a resistor to allow for slow start up to avoid inrush currents. when the desired charge is reached, a relay will bridge this trickle charging system to allow full power and also start the receiver. since your fuse was blown, it's possible (theory only) that one of your caps or even a bridge rectifier has shorted and is not allowing for the voltage to reach its peak, which btw must be the reason why you didn't blow out the new fuse you put in ? if this is the case, you should have a high wattage resistor getting vary hot!, or maybe by this time has opened or unsoldered it self from the board ?
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A shorted rectifier or main filter cap would blow the fuse every time, not just the first time.
The receiver in question has a DC and current detect circuit, not a simple R/C delay for the relay.
There is only a small chance that the OP's receiver can be repaired at all, since the main output IC is no longer available, and is VERY likely the fault. The only definitive way to know for certain is to troubleshoot with a service manual and a knowledgeable technique. Since the OP has neither of these, money spent getting a repair estimate is a low-percentage proposition (free estimates are a thing of the past). Add to this the fact that it wasn't one of Yamaha's best to start with, and there is near-unanimity on the group, including the OP, that the receiver should just be replaced instead. New and high-quality vintage gear abound.
Have you ever worked on one of these? Trying to help is a good thing, but posting speculation when you have no idea about the design and typical failures in the specific unit is less than helpful. Sounds like you have no idea what you are talking about or you did not pay attention to the post. If the bridge was blown he would have never get it to do anything but blow more fuses immediately.
The only thing typical in these units in the power supply might be some dried up glue around the caps that eats up leads on parts and jumpers when it absorbs moisture from the air. The OP has already received good advice not to waste any resources on this one from people who have extensive experience with them. Don't send him chasing his tail.
No need to. Mark already did. Too bad I missed his post before I responded. It was much more precise than mine...half-baked goobledygook...LOL. As usual, he nailed it.
never said it was a simple RC circuit, i think i said something on the effects of sampling the voltage?, this implies its looking for a desired level. and many upper end units use separate source from the main bridge and caps to operate this little circuit!. it is very possible for a bridge or cap to have a short with the trickle charge R being on the AC side of the transformer into the bridge. this would protect the fuse from being blown out again since the monitoring of voltage never reaches its level via the low current charge Network that is being used. if problems arise while in operation then it would make sense for the fuse to be defective since the PSU would have this low current R bypassed and over current would have been seen.. defects could also lead to Audio output being shorted which i also connected to the supply during charge up. this form of protection is able to monitor both PSU and attached devices. so it's very common to find fuses blown during operation and not blow after you replace them,. this generally means the PSU has not met its desired peak level of charge before the by pass contactors/electronic switch are connected.
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No, you never exactly said it was a simple RC circuit - but that is what is required for a simple time delay prior to the relay activating. There is no such circuit in the Yamaha. All it's "looking" for is an absence of a DC offset at the output of the amplifier, and possibly excess current flow, though I'm doubtful that feature existed on this low-end model. I have the service manual at work, but I'm not even going to look it up because it's really irrelevant to the point.
and this:
is either PURE gobbledygook, or you simply have problems expressing what you are really trying to say. I'm not trying to be insulting here, by the way, but you have posted generic advice without labeling it as such, and that advice:
Is faulty in general terms.
Does not apply to the specific model the original poster had, while at least 2 or 3 other replies were from knowledgeable techs who have actual experience on this model.
Newer models, mainly over-engineered surround models, do have more sophisticated protection and diagnostic features, but that's not even what you were _trying_ to talk about. I'd like to point out again that this is a lower-end, older receiver, around
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