Diagnosing a Transformer

Discussion in 'The Projects Forum' started by wanders, Feb 9, 2012.

  1. wanders

    Thread Starter New Member

    Jan 19, 2012
    I'm new to electronics and am working to diagnose the problems with a non-operating, Pioneer RT-909 reel to reel tape deck. While there is electronic power to the unit, there is no power to any of the mechanical functions. I've found and replaced some bad capacitors and have spotted a few questionable transistors, but these have not resulted in any changes. The schematics show few voltage specifications, however, they do show that, from the transformer to the reel motor control circuit board, the specified voltages are 125 and 85 vac for each motor. My readings, directly from the transformer are 78 and 38 vac for one motor and 52 and 23 vac for the second.

    Based on these readings, is it reasonable to conclude that the transformer is faulty?

  2. JDT

    Well-Known Member

    Feb 12, 2009
    Transformers usually fail in one of two ways:-

    • Open circuit - no output voltage at all
    • Shorted turns - reduced output voltage but in this case often get very hot (so smoke is usually seen!).
    So I'm not sure either case applies to your transformer. Might be something else.
  3. GetDeviceInfo

    AAC Fanatic!

    Jun 7, 2009
    as I suggested in your other thread, you'll likely want to isolate those circuit branches. Your circuit is likely overdrawing on the transformers and your experiencing a resulting voltage drop. How did you overcome the fuse blowing? At minimum, you need to remove the mechanical load from the motors.
  4. wanders

    Thread Starter New Member

    Jan 19, 2012
    Truth told: I unseated one of the pcb's to get at the other side and, apparently, allowed some of the connectors to touch the brace (ground), thereby blowing all the fuses.

    Guess that means you don't think the transformer is bad. If I remove two of the leads, at the board, where I took the readings, connect them through the multimeter, the reading should be 125 vac? And, if so, I can conclude that the transformer is not at fault.

    Thanks for the help.