Rullebör

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  • in reply to: Beolab Penta 2 running hot, can’t adjust bias #9623
    Rullebör
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    Impressive work, it really does look better! Maybe I’ll try something similar in the future if I can’t find covers.

    in reply to: Beolab Penta 2 running hot, can’t adjust bias #9606
    Rullebör
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    Gotta ask, what is the alternative solution? Been trying to locate them online and through B&O with no luck…

    in reply to: Beolab Penta 2 running hot, can’t adjust bias #9141
    Rullebör
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    My dudes, thanks to everyone for your guidance! The amp is up and running with well-adjusted bias and offset.

    After both reflowing the suspicious looking transistor joints and replacing the lifted ground trace everything seems to work just fine. Hard to tell if it was the ground trace already making troubles before I started working on the amp or if it was the transitors soldered. Since they had obviously been serviced before and the soldering suggests work on the transistors both issues could have arisen through sloppy soldering.

    Happy to save these from becoming beovoxes : )

    Now I just need to find an intact yellow display cover…

    in reply to: Beolab Penta 2 running hot, can’t adjust bias #8994
    Rullebör
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    I also thought so but checked the ohm with dmm in circuit and it’s correct. One thing that puzzled me was that while turned the 220 trimresistor would read above 220 ohm and after turning off would steadily decline down to the ~110ohm it was set to. Something to do with how the circuit design or indicative of a fault?

    Thanks for the guidance, I’ll go over the board once more and inspect the joints more carefully. Afraid I have a hard time making out the crack on pin 7 in the pic but gives me an idea of what to look for.

     

    in reply to: Beolab Penta 2 running hot, can’t adjust bias #8982
    Rullebör
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    Thanks, really appreciate it!

    Yes I replaced the psu capacitors. Problem is now amp is going into protect mode again, too fast to get a measurement on the +/-68V.

     

    Transistors look fine to me but will check more closely.

    I have not reflowed the points of board connectors since I left them in, should that be done?

    I found a lifted trace at the ground wire that might have lifted more now, trying to fix it with wiring. So that’s the weird thing in the middle of the picture of the trace side of the board.

     

    20220924_17573520220924_180449

    in reply to: Beolab Penta 2 running hot, can’t adjust bias #8927
    Rullebör
    BRONZE Member
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    Yes, using the ones from the beoparts package. R59 adjusts offset just fine but R95 can’t get the bias down to the 30 mv range. Setting R95 at anything but minimum activates protection circuit and orange light.

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