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Yamaha SPX 90 II service notes?!

Discussion in 'Electronic Repair' started by n8ball, Feb 7, 2009.

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  1. n8ball

    n8ball Guest


    Currently working on a Yamaha SPX 90 II Digital Reverb unit and would
    love to have the service notes, at least

    for the power supply....

    Anyone have this available?

    I found it for sale online but rather not pay for them unless i have



  2. N_Cook

    N_Cook Guest

    a "repair " note for a failed to repair one. I even worked out the schematic
    but could not find the reason for the slightly linear ps characteristic, not
    full switching, and then thermal runaway. Even tried rewinding the secondary
    of a generic smps toroid and could get it reliably working but only with a
    fan. There was some shorted turns in the original, presumably due to excess
    heat build up, but before blowing the TOP66 chopper. In retrospect just
    enough space for 2 squat linear tx and retaining the ac throughput circuitry
    built onto another board

    Yamaha SPX 90, 1986 , Digital Multi Effects Processor
    Cold checking , have found 2 things wrong with the ps so not powered up yet
    No SMPS controller IC on the ps board , a TOP66 switcher driver and 3 small
    Raw + and -18V go to main board +/-15V regulators , raw 5V , ie rectifier
    off the switching transformer followed by one L and one C goes straight to
    the 5V TTL rail. Not even an obvious fat 5V zener across it.
    No SMPS controller IC , that I can see on the main board and the 2 lines
    from the main board marked PE and PC that go to the mains side of the ps via
    opto isolator .
    There are 15 assorted wirewound resistors on this ps , again rather odd.
    If I get it working , a ventillation hole and grill cut in the top cover
    would help.
    It was that hand over period , 80s , when phenolic pcbs went over to
    This Yamaha has polyester main board and phenolic light brown ps pcb that
    has a lot of heat dark browned/brittlised? areas. Not surprising with
    assorted 15 W/W plus sm driver etc with no ventilation holes anywhere.
    Got it back to working to its earlier non-working condition before it was
    mangled by a "repairman".
    Can now see that the original problem was an 85 dec C electro that did not
    like being cooked in there.
    I determined the schematic for this SMPS
    The 5V regulation, unlike the +/-15V, is on the ps itself, in discrete form,
    consisting of 300mW zener,preset and TO92 transistor.
    Working at 2/3 mains coltage but temp of the chopper transistor goes too
    high, if I let it, and power consumption goes well above 20W.
    Looks as though something has gone wrong with the mark/space control.
    It slowly increases so the "5V" line goes 2...3V and then jumps to 5V with
    equal mark/space which is presumably not necessary.
    I checked there is no excessive load on the +/-18V or 5V rails despite
    all functions working as far as front panel display.
    To get a rough idea of the amperage capability of a small 5V SM ps
    before attaching it to its load, to simulate, just in case the regulation is
    It uses a TOP66 of sufficient rating to
    drive a few hundred watts across but the ps is relatively low power , but
    unknown rating.
    The one in question is only about 20mm cube
    I've fathomed out how the ps works. The 5V regulator uses only a 100mA TO92
    transistor because the error is fed forward via an optocoupler to the sm
    The 5V line defines the output to +/-18V as well.
    The original trouble was wavering 5V, which has returned, prior to replacing
    some more caps . In the broken mode if say 2.5V on the 5V o/p then only
    +/-10V on the unloaded +/-18V lines.
    Scaling linearly, an at hand 70 W smps, with its 45mm cube transformer.
    I would estimate volume for vol then this one with 20mm cube would be about
    6W total. Allowing 1W for the few op-amp supplies and 2 relays then only 1
    amp at 5V, its suppling 30 odd 74HC and 3 LSI.
    When operating properly the oscillation is about 59 KHz with equal
    mark/space ratio,
    when at half-cock then about 40KHz short mark/ space
    The consumption plate states 20W, assuming average SMPS 70 percent
    efficiency then 14W at DC.
    uses 2SC2792, 2SC2634 /2034?, 68uF/400V, 2x 1R FR
    3 x 100K w/w ,6.8,2x 68K,22,2x 330, 2x 120K, 6.8, 1.5, 22, 27
    2 fuses marked micron63 FN191R0J
    6.8,100R on main board
    The second optocoupler is the other way round.
    Feeding rectified but unsmoothed mains signal info to the main board.
    Phase info for mains hum/noise reduction?
    6.2V zener on ps for 5V regulation section.
    In working order but short duration of 65 percent mains
    load was 85mA on -18V line, 128mA on +18V, and 360mA on 5V
    so 5.6W (placing 0.5Rs and 0Rs between plugs and sockets)
    At 70 percent mains was getting 2.5V on '5V' and -10.5V on '18V' slowly
    building up to 5V, feeds forward via pc1.
    Replaced main chopper transistor, D1207, 2x6,8 to 12R, 2x 330 to 2x1000, 22
    to 68
    and 1.2K 1/3 watt setting chopper bias to 390R and unnecessarily replaced
    PC511 just
    in case.
  3. n8ball

    n8ball Guest

    do you have the schematics that you worked out...

    I found a site that explains the different switched mode power supply
    designs (AC filtered and rectified to DC then back to high frequency

    which design is in the yamaha spx? I replaced the large cap (which
    was blown it was bulged out on the top) and the other caps on the
    "secondary side"

    I dont get anything on the power connectors

    what else is prone to failure? what should i check next? the AC
    goes to a fuse, switch, and them to L1/L2 with 4 caps (i assume this
    is the voltage being dropped and filtered....what is that transistor
    with the heat sink for....voltage regulator?


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