1. Rest in Peace Paul (Kegger) If you would like to help the family in this time of great sorrow and need, you may donate on their GoFundme page: https://www.gofundme.com/mckechnie-medical-and-funeral-fund?
    Dismiss Notice

Marantz 1090

Discussion in 'Marantz Audio' started by caesar56, Jul 15, 2017.

  1. caesar56

    caesar56 Active Member

    Messages:
    188
    Hi there fellow members.

    This time I'm requesting a little help with my 1090 Wich does not make sense to me.
    After upgrading/restoring the amp following carefully Leestereo's thread, (My only deviation were 10kuf/63v main caps) my amp burned a couple of 100ohm 1/2 resistor R801 in the service manual (One after replacing the other).
    After a little bit of troubleshooting with a DBT I discovered that after Diode Q806 I should have 44V but as a matter of fact I have 55V.
    This does not make sense to me because right before the diode and after R807 I have the correct 43.8V

    The amp was modified before and I don't think the diode is original. But maybe I'm overlooking something else.

    Any guidance is greatly appreciated.

    C.
     
    Last edited: Jul 15, 2017
  2. Richs_Trains

    Richs_Trains AK Subscriber Subscriber

    Messages:
    626
    Location:
    Tucson, AZ
    If it worked before the re-cap then I would check the polarity n all the caps replaced against the SM. The silkscreen on the PCBs have been known to be wrong. Folowing Leestereo's thread would not cause a new problem, so my guess is something is installed backwards. Good luck Rich
     
  3. rBuckner

    rBuckner Luv 2 Restore Subscriber

    Messages:
    9,019
    Location:
    Prescott, Arizona
    It's because it's unregulated so depends on the line voltage and the load at the time of measurement. Not to worry about it.
     
  4. caesar56

    caesar56 Active Member

    Messages:
    188
    Ah, so that's it.
    I've noted that the resistor in question does not like the inrush current and tries to fry itself when I turn the amp on.
    I used a higher wattage one and it holds it's ground but gets quite hot. I don't consider this an ideal solution however, it could be the higher value capacitors.
    There's one thing that buggers me, since Ben changed so much in the circuit, I'm wondering if the voltage values present in the SM as testing points are still valid.
    Thanks a lot in advance.
     
  5. Leestereo

    Leestereo Super Member

    Messages:
    1,833
    Location:
    Ottawa, ON
    If I understand your measurements, the value of 55V between the zener Q806 and the 4.7kohm (R807) is indeed odd, if you are measuring 44V before the zener (i.e., at R801). What are the measurements on Q803 and Q804? The problem lies "downstream" from the regulated supply; something is drawing too much current (it would not be the indicator lamp that is fed by Q806 and R807). Note that the relatively modest increases in the capacitance values of the circuit will have minimal impact on the measured voltages as per the schematic (with the amplifier at idle).
     
  6. caesar56

    caesar56 Active Member

    Messages:
    188
    Hi Lee, thanks a lot for the reply.
    Just to clarify. After the 4.7kohm resistor I have 43.8V wich go straight to the zener next to the black double diodes, then between the zener and the 100ohm resistor in the PSU circuit the sm says I should have 44v but I have 55v.
    I had to raise the wattage of this resistor, I'm pretty sure there's a lot of current going somewhere but the amp works and adjusts idle current as it is.
    I don't see anything overheating or burnt. The pre is working as usual.
    This is a big :eek: for me.
     
  7. Leestereo

    Leestereo Super Member

    Messages:
    1,833
    Location:
    Ottawa, ON
    The regulated power supply only feeds the phono and preamp stages (not the power amp stage); take voltage readings and post your results.
     

Share This Page