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

Discussion in 'Electronic Repair' started by Dave, Apr 13, 2007.

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  1. Dave

    Dave Guest

    I have an old Yamaha CR-820 receiver/amplifier that no longer has any sound
    output. The meters still show signal strenght when a tune across the AM/FM
    bands but I get no audio from the speakers or the phone jack. No hiss. hum,
    carckle or pops. JUst solid dead silence.

    It isn't worth sending out for a shop base repair.

    Has anyone has a similar problem? Does anyone know where I can obtain a
    schematic or service manual?
     
  2. Arfa Daily

    Arfa Daily Guest

    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
     
  3. 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.
     
  4. Dave

    Dave Guest

    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.
     
  5. Arfa Daily

    Arfa Daily Guest

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

    Arfa
     
  6. 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.
     
  7. If there's no sound I think I'd look at the regulated power supply areas
    first...

    Mark Z.
     
  8. Arfa Daily

    Arfa Daily Guest

    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
     
  9. 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.
     
  10. David

    David Guest

    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.
     
  11. Dave

    Dave Guest

    .. 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.
     
  12. Jamie

    Jamie Guest

    or you put something in wrong.
     
  13. me

    me Guest

    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)
     
  14. Arfa Daily

    Arfa Daily Guest

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

    Arfa
     
  15. Arfa Daily

    Arfa Daily Guest

    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
     
  16. 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.
     
  17. Arfa Daily

    Arfa Daily Guest

    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
     
  18. Dave

    Dave Guest

    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.
     
  19. DaveC

    DaveC Guest

    It has been fun playing with this. I salvaged it from the recycling heap. It
    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.
     
  20. Dave

    Dave Guest

    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!
     
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