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Yamaha RX-V992 won't power on

Discussion in 'Electronic Repair' started by Bob E., Mar 10, 2013.

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  1. Bob E.

    Bob E. Guest

    Pressing the power button gets relay click and power LED flash (on volume
    control) but all shuts down immediately.

    Looked for infamous "pink cap" on "sub power supply" (there is one) and
    replaced but no change in symptoms.

    Jumpered the relay contacts and using a Variac ran voltage up full (while
    watching main transformer secondary voltages): all seems normal but still no
    signs of life. Transformer voltages are as expected (2 pairs of windings;
    each pair share a common center tap, total: 4 windings, all voltages increase
    linearly with increase of primary V). Still no display or control
    functionality at all.

    Pressing the power button (with jumpered relay and full mains voltage
    applied) gets same symptoms.

    So far I think I can rule out a shorted output device.

    How best to proceed with the troubleshooting?

    Ideas?

    I have the service manual.

    Thanks.
     
  2. N_Cook

    N_Cook Guest

    voltages increase linearly and match + and - ?
    Any SIL protection device eg (uP)C1237 , get the data on it and work around
    its inputs and outputs , could be IC failure or genuine bad/erroneous bad
    input
     
  3. N_Cook

    N_Cook Guest


    If microcontroller based, then similar sort of skirting around process, but
    not so easy working out the relevant inputs/outputs
     
  4. Bob E.

    Bob E. Guest

    I removed the temporary jumper from across the relay contacts. And:
    Let's talk function and not label... The obvious "pink cap" (0.01 uF/50v) is
    across the ~12v secondary of the small transformer near the AC input. It is
    an AC filter cap. I measured 4 vac across it. Replaced with a mylar and it's
    a reasonable 12 v now.

    Here's that little PCB:

    http://www.tinyuploads.com/images/8O0dYH.jpg

    I replaced C312.

    Any other suggestions?

    The supercap (0.047F / 5.5v) on one of the function PCBs is obviously leaking
    and corroded. I removed it (it caused no further damage to the PCB) and will
    get a replacement today. Shouldn't the unit boot if this was the cause of
    pulling down the 5v line (I'm guessing at this -- haven't found it in the
    schematic so don't know what, exactly, it's hooked to...)?

    Symptoms remain unchanged with new filter cap and removed super cap.

    Ideas welcome.

    Thanks.
     
  5. Bob E.

    Bob E. Guest

    What do the extra labels mean next to many of the components on the
    schematic?

    Next to a transistor is its label "Q302" and next to that is "s10".

    Just on this small board there are these extra labels from "s10" through
    "s37".

    http://www.tinyuploads.com/images/8O0dYH.jpg

    What is this "s" designation for?

    Thanks.
     
  6. Guest

    Looking at the schematic, it might indicate a part whose value changes
    (or is/is not installed) based on which version of the board is being
    used. Note that parts with the "s" labels don't have a specific value
    listed - compare C308, marked just "s14", with C307, marked "1000/25".
    Also note that the fuses and transformer all have "s" labels; these
    parts often are different for a power supply with 120 V vs 240 V input.
    Also, it doesn't make sense to have J301 and Q302 installed at the same
    time; J301 would just bypass Q302 in that case. Both J301 and Q302 have
    "s" numbers. Somewhere on the schematic or in the manual there should
    be a table of "s" number to part number based on the version of the
    board.

    To your original problem, have you tried unplugging CB304 and measuring
    the voltage across +MB and G, or across C307? Those should be pretty
    close to 12.5 V DC. If you have a scope, also measure the same place
    for AC ripple; if you don't, put your multimeter on AC and measure the
    same place - you should have much less than 1 V AC. If there is a lot
    of ripple, check C307 and C308.

    Matt Roberds
     

  7. I can try to help. You can email me at:



    and reverse labolgcbs to read "sbcglobal"

    Mark Z.
     
  8. Bob E.

    Bob E. Guest

    Replaced the supercap (0.047F/5.5V), no joy. Same symptoms.

    The "+MB" 12v line coming from the "sub power supply" board is 14.2v with
    very little (0.05V) ripple.

    The "switch on" signal (PRY) that runs the mains relay comes from the main
    controller, IC1 (HD643361-A49P).

    I jumpered manually the PRY signal from the 12v (actually 14) to the PRY
    line. This gives the same symptom as pressing the power button: mains relay
    clicks, volume control LED lights and goes out.

    Not being to check DC voltages at the pins on this IC (we're not powered on
    yet) the schematic does call out 2 scope checks to do on IC1: the oscillator
    signal for; and the RESET signal which triggers when the mains input cable is
    connected (and, curiously, NOT when the power switch is pushed). I'll check
    these tomorrow.

    Thanks.
     
  9. Bob E.

    Bob E. Guest

  10. Jamie

    Jamie Guest

    THis maybe a stupid suggestion but, I've found this many times in sub
    micro processor units that get moved, hit, vibrated etc... Have you
    check to see if the processor has a xtal and is so, is it operating?

    Many times the crystal will break loose from their connections inside,
    due to vibration...

    Also, I saw another piece of equipment that monitors the elimination of
    a florescent display, if no light, no processor. Basically if that part
    of the circuit fails, the rest will wait. That makes perfect sense
    because you don't want to be operating blindly on some equipment.

    Jamie
     
  11. Bob E.

    Bob E. Guest

    THis maybe a stupid suggestion but, I've found this many times in sub
    Not stupid at all. As a matter of fact the Yamaha factory service manual says
    that this is one of the first steps to take when diagnosing (I now see after
    rereading this section...)

    I'll look at that next.

    Thanks.
     
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