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    PAS 2 - Normal Behavior?

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    Pillo69

    Posts : 105
    Join date : 2012-04-11
    Location : Granada (España)

    Re: PAS 2 - Normal Behavior?

    Post by Pillo69 on Sat Sep 10, 2016 2:39 pm

    You have tried to connect to another line input PAS ??.

    Peter W.

    Posts : 142
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: PAS 2 - Normal Behavior?

    Post by Peter W. on Sat Sep 10, 2016 3:26 pm

    Yes, he has. So, we are trying next steps as there is clearly a problem with the preamp itself. This is the difference between the unit in front of me and the unit somewhere else. Most of the individuals here with experience would have found whatever the issue is already. It is much harder to find it through another, not so experienced, pair of hands. But I am sure it will be found.

    rodneyk915

    Posts : 16
    Join date : 2016-08-29

    Re: PAS 2 - Normal Behavior?

    Post by rodneyk915 on Sat Sep 24, 2016 3:13 pm

    Just a breif update,

    I opened it up and took another look around because there was also a hum going on. I pulled all tubes and sprayed deoxit on them and worked them in and out several times. I discovered a wire that must have gotten trapped between the chassis and bottom plate because it had about a 1/4 inch of insulation missing. I relocated the wire and took some measurements on the quad capacitor and rectifier as well as Pins 16 and 19 on PC 5 and Pins 16 and 15 on PC 6. I got very high readings that I don't believe could possibly be right. All readings were with the unit plugged in and meter set to 300 v~

    On the 12x4

    1   342  (335)
    2     0    (  0 )
    3     0    (  0 )
    4     10  (10.5)
    5     0     ( 0 )
    6   343   (335)
    7   931   (405)

    Capacitor

    1   937   (405)
    2   774   (335)
    3   690   (330)
    4   468   (210)

    PC 5

    Pin 16    675
    Pin 17     25

    PC 6

    Pin 16    462
    Pin 15    25

    I just received another quad cap but have not installed it. Not sure if that is the culprit. After relocating the wire and closing it back up unit is dead silent and volume works correctly for the right channel but still bleeds through on the left so further investigation needed there. Opinions about the voltage readings would be appreciated. Thanks.

    Peter W.

    Posts : 142
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: PAS 2 - Normal Behavior?

    Post by Peter W. on Tue Sep 27, 2016 1:12 pm

    >>I just received another quad cap but have not installed it. Not sure if that is the culprit. After relocating the wire and closing it back up unit is dead silent and volume works correctly for the right channel but still bleeds through on the left so further investigation needed there. Opinions about the voltage readings would be appreciated. Thanks.<<

    https://www.manualslib.com/manual/1006756/Dynaco-Pas-2.html

    The above is a link to the PAS2 manual, look to the function served by the crimped wire on the right channel, then trace the same function for the left channel. DO NOT assume that the unit was correctly assembled in the first place, but check everything. Then:

    I have to ask, have you recapped *all* the small-value caps? Start with everything on PC5 as that will be the most likely place where a shorted cap may cause you problems - as it applies to all sources. That is 'not many' caps and perhaps a couple of hour's work doing both channels. Mouser et.al. will sell you the parts, go with 600V-or-more caps.

    Keep at it! You are already 50% there!

    rodneyk915

    Posts : 16
    Join date : 2016-08-29

    Re: PAS 2 - Normal Behavior?

    Post by rodneyk915 on Wed Sep 28, 2016 8:09 am

    Thanks Peter! Personally I have not recapped anything. As far as I can tell, the previous owner only removed the selenium rectifier, replaced the filter caps, and added diodes. Everything else looks original including the dynaco tubes. I was contemplating getting one of those mica / metal film capacitor upgrade kits from ebay to replace the current ones.

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