Yamaha CR-820 Repair: No Output, Tuner shows signal received.

If it's nothing straightforward like a failed ( rather than blown ) fuse, then it's most likely that the speaker protection circuit is operating because of a blown output stage. I've a vague recollection that this one uses an output hybrid ( big black "IC" bolted to the heatsink with type STK-xxx ) and if so, it is likely that this is your problem. Some of these can be very expensive, and many of the older ones are now obsolete and hard to obtain. If it is one of the models that uses discrete output stages, then you might struggle to get to the bottom of its problems, particularly without a set of schematics, which again, might be difficult to find for an item this old.

Arfa

The CR-820 uses discrete transistors, but the repair isn't for newbies - there's fusible resistors inside asbestos tubing which go bad, usually without any visible clue, and the layout is hardly service-friendly.

Mark Z.

Thanks for the information all.

Yes there are 4 heat sinked bipolar transsitors. They cost about $10 each. They get warm to the touch.

I bought a service manual for $15 bucks.

I will see what I can find out. This was a friend's unit.

I wil check out those fusible resistors.

OK, much like the modern Yammy AV amps then ...

Arfa

Well, they aren't flat packs - they're TO-3's - 2SB557 and 2SD427 IIRC.

Four-gang (once again, IIRC) tuner, all analog, silver face, wood cabinet, rectangular metal knobs, and lots of 14 volts lead-lamps which burn out...

mark Z.

If there's no sound I think I'd look at the regulated power supply areas first...

Mark Z.

I was being facetious Mark, and referring to the fact that it's layout is not very service friendly ...I went to a Yammy training seminar recently, and the national service manager told us that the average turnaround time on an AV amp for a Yammy dealer, was 22 days, which was really too long, and could anyone venture a suggestion as to why this was. I told him that the first 16 days were spent looking at it sitting on the shelf, hoping that it would go away. The next 3 were spent trying to work out what the internal diagnostics were trying to tell you. The next 1 was spent trying to strip it apart and work out which screw was still holding it. The next day was spent fixing it and putting it back together, and the final day was spent either rejoicing that you could write a bill out for it, or crying whilst watching all the magic smoke being released again ...!! Sound about right ? d;~}

Arfa

Sound

Absolutely. I just got in an RX-Z9, lightning struck. Can't tell you how much I'm looking forward to that one...

Mark Z.

It appears one of the output devices is shorted. For $5 I may try a repair. I did not see the fusible resistors. There is also a relay. I suppose it could be bad.This doesn't seem to hard to get to many of the components.

It looks like one of the power stages was repaired before as it use RCA SK---- devices.

. If I run the amp with both left channel transistors out of the circuit the right channel works fine. I replaced a bad outout transistor after checking it. Now when I turn the receiver on the main power fuse blows.

My guess is that the original failure took out the power transistor before the fuse blew.

or you put something in wrong.

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"Dave" wrote in news:ALTUh.10924$ snipped-for-privacy@newssvr27.news.prodigy.net:

Your best bet is to replace all output transistors (left and right chanel), check all the smaller transistors in the area, and check the emitter resistors for the outputs (usually 2 small value {~.47 ohms or less} resistors in one 3 pin package with a common leg in the middle)

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Welcome to the world of DC coupled amp repairs ...

Arfa

Hey Mark

Have you done much with the RX-Z1/DSP-AZ1 ? Have you had any problems with the 4 pin 5v regs? I've got one in at the moment. Runs absolutely fine for about 20 mins, then starts cutting out, back to standby. Re-powers with standby switch, but about 1 second only. Diagnostic memory says PS Prot :

016 K/L and then some stuff referring to the processor rev numbers. Don't know about you, but I have a hard time ever making any sense out of those Yammy diag messages. " PS " rather than " DC " says power supply rather than output offset protect, but what is " 016 " trying to tell me ? I seem to recall that it refers to a percentage error on a rail, but that there are two different schemes used for the reference. Today, I went down the path of pulling out the sub psu board to the point where I could get at it to take some measurements on all the regs on there. With the meter on peak hold, I caught the output of IC451 going up to 8.54v just before it tripped out. Now I reckon that's about 160% up on the correct 5v, so is that what " 016 " is trying to say ? Interested as to whether you have had anything similar. I've got a replacement coming tomorrow, so should know within 20 minutes of turn on, but already, no matter what I charge for the repair, I'm actually going to be down when you count in all the time to dismantle, trouble shoot, and reassemble. Without doubt, I'd have to say that Yammies are among the worst of the current crop of AV amps for service and repair. They are just not friendly at all in any area - electronic design, mechanical design and user interface.

Arfa

I have had that exact problem on one - and the regulator fixed it just fine - no other damage done.

I've never bothered to try to decipher those DC error levels. They are based on 5 volts, as I recall.

Mark Z.

OK, well that's good to know. The reg didn't actually turn up today, so hopefully tomorrow. You are right that the error figures do relate to 5v - I can remember the little Japanese guy that lectured me on it originally, saying so, but his english was not too good, and I was having enough trouble just trying to stay with that, let alone the in-depth meaning of what he was actually saying. I definitely do remember him saying that there were two different schemes as to how the figure related to 5v though. Shame really, as he was a very clever guy, and clearly knew these beasts inside out, but boy, was his lecture hard work to understand, just purely from the linguistic point of view.

And then, of course, we had Mr Beardy in the class, who stopped the poor little guy every six sentences, and took him, and the whole class, off on a tangent about some obscure problem that he'd had 10 years ago, for 15 minutes. I'm sure that you've been there ...

Thanks for confirming my suspicions about the 5v reg - I'll let you know !

Arfa

It has been fun playing with this. I salvaged it from the recycling heap. It looks like I will be scraping it an dselling the parts on eBay.

Thanks all for the information.

Wait! When an output device goes, doesn't it frequently take the driver stage transistor with it? Look back "up" the power output train for a shorted tranny before binning it.

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I will give that a look before I do anything. All I have is a couple DVMs and a transistor checker but I can do quite a bit with this limited test package!