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    pas3 phono

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    opa1

    Posts : 8
    Join date : 2012-08-31

    pas3 phono

    Post by opa1 on Fri Sep 07, 2012 3:18 pm

    I have a pas3 thats new to me. I'm having problems with the phono section. The right side volume is alot lower than the left. Other inputs work fine. Its not the turntable. It works ok with different preamp.
    What should I look for to fix it?

    Thanks

    Bob Latino
    Admin

    Posts : 2374
    Join date : 2008-11-26
    Location : Massachusetts

    Re: pas3 phono

    Post by Bob Latino on Fri Sep 07, 2012 4:25 pm

    Some things to check ...

    1. A bad contact on the selector switch. Try spraying the contacts on the selector switch with electrical contact cleaner and cycling in and out of the phono mode. Sometimes a bad contact on the selector switch can cause low volume

    2. The phono board inside the preamp is the board nearest to the selector switch and the RIGHT channel part of the board is the part closest to the front of the preamp. The LEFT channel usually has GREEN wiring and the right channel usually has RED wiring. If your right channel is bad take out the right channel's 12AX7 and clean off the pins and reinsert the tube. If that doesn't do it then swap the two tubes on that board and see if the problem moves to the other channel. If it does - then that 12AX7 is bad.

    3. Try cleaning the TAPE/INPUT switch with contact cleaner and cycling the switch back and forth a few times.

    Bob

    opa1

    Posts : 8
    Join date : 2012-08-31

    Re: pas3 phono

    Post by opa1 on Fri Sep 07, 2012 4:53 pm

    I'll try cleaning. I do notice when playing in phono mode, If I touch the right tube the right channel[red wires] hums. If I do that to the left[green wires], no hum. I switched the tubes, no change.

    opa1

    Posts : 8
    Join date : 2012-08-31

    Re: pas3 phono

    Post by opa1 on Fri Sep 07, 2012 6:30 pm

    I tried deoxit. No change. The unit has some kind of updated boards in it.Ps is updated to.

    Bob Latino
    Admin

    Posts : 2374
    Join date : 2008-11-26
    Location : Massachusetts

    Re: pas3 phono

    Post by Bob Latino on Fri Sep 07, 2012 6:34 pm

    See if you can post a photo of the interior wiring. Check out the sticky on the main "basket" of the forum for instructions on how to place a photo in with the text of your post ...

    Bob

    opa1

    Posts : 8
    Join date : 2012-08-31

    Re: pas3 phono

    Post by opa1 on Fri Sep 07, 2012 6:48 pm

    http://audiokarma.org/forums/showthread.php?t=462544 There is a photo here.I dont know if link will work. If I'll photobucket one up.

    opa1

    Posts : 8
    Join date : 2012-08-31

    Re: pas3 phono

    Post by opa1 on Sat Sep 08, 2012 12:45 am

    I did some voltage checks on the 12ax7's.
    LT RT
    1=106.5 1=102.7
    2=0 2=0
    3=.6 3=.21
    4=0 4=0
    5=11.1 5=10.94
    6=126.5 6=128.8
    7=0 7=0
    8=.7 8=.6
    9=5.6 9=5.5
    Looks like the cathode section 2[#3 pin] is low for the right 12ax7. Now what do I look for?
    Thanks,
    Mark

    hawaii.ken

    Posts : 157
    Join date : 2012-01-31

    Re: pas3 phono

    Post by hawaii.ken on Sat Sep 08, 2012 7:19 am

    The photo link does not work for me.

    Double check that the knob for balance control is positioned properly on the pot.

    Next, connect the leads from the turntable to the "Special" input and move the selector switch to the same.

    After warmup, play a record on your turntable. It won't sound right but notice if the volume is balanced.

    opa1

    Posts : 8
    Join date : 2012-08-31

    Re: pas3 phono

    Post by opa1 on Sat Sep 08, 2012 10:23 am

    I tried that already. No change.

    tubes4hifi
    Admin

    Posts : 1261
    Join date : 2008-11-30

    Re: pas3 phono

    Post by tubes4hifi on Sat Sep 08, 2012 11:16 am

    do you have the schematic? The cathode is connected to a 1K resistor, but is also connected to the RIAA EQ negative feedback loop,
    and also to the 3rd position of the selector switch.

    opa1

    Posts : 8
    Join date : 2012-08-31

    Re: pas3 phono

    Post by opa1 on Sat Sep 08, 2012 12:14 pm

    I looked at the schematic. Pin 3 and pin 8 should read the same. I see what your talking about. The fb is going to the plate with a .05 cap and a 1.2m resistor correct? I'll trace it out and try to check values.

    opa1

    Posts : 8
    Join date : 2012-08-31

    Re: pas3 phono

    Post by opa1 on Sat Sep 08, 2012 5:03 pm

    I fixed it. The #5 connection on selector was connected to the #5 on board. It should be connected to #6. I wonder how long it was that way!!
    Thanks for the help,
    Mark

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