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Adcom 5400 amplifier blowing all fuses

Discussion in 'Audio' started by Audiofreak1, Sep 20, 2018.

  1. Audiofreak1

    Audiofreak1

    32
    2
    Sep 20, 2018
    Ok now I installed 6 electrolytic capacitors on each board. The left side of the amp is fine. Everything checks out so far. Oh the thermal protection light on the left side does not light up on plug in. DC offset was good bias was good. The right side went distortion alert bright as all can be. I read the dc offset and it was out a good bit 3.78 so I went to adjust it a little and turned it up the whole way and the distortion light went off. Also the right side get warm quick and then starts to get to running tempitures I would say 10 minutes. While the left side started to loose its chill. Ok well not sure what sparked this. Well I am calling it will refresh and get back at it.
     
    Last edited by a moderator: Oct 16, 2018
  2. davenn

    davenn Moderator

    13,168
    1,713
    Sep 5, 2009

    good chance you have put one or more in around the wrong way
     
  3. Audiofreak1

    Audiofreak1

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    Sep 20, 2018
    Thats what I was thinking I will double check all my caps. Only thing I can think of is the one cap might be wrong it’s a 4.7uf 25v
     
  4. VenomBallistics

    VenomBallistics

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    26
    Aug 30, 2018
    check .....
    Q614
    D610
    SOMETHING is borked enough to drag the the OPS to the neg rail.
    Interestingly, your amp looks to be of a design that's fairly easily scaled, provided you have the power transformer to feed it.
    Just add OPS pairs, gate and balance resistors.
    Nice thing about MOSFET amps is that they are immune to thermal run away, thus omitting a somewhat confusing section of circuitry.
     
    Audiofreak1 likes this.
  5. Audiofreak1

    Audiofreak1

    32
    2
    Sep 20, 2018
    Here is my one drive link to the pictures of the amp https://1drv.ms/f/s!Ai1_z2pX1K8PhXJPCSzpxIzifHaZ
     
  6. Audiofreak1

    Audiofreak1

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    Sep 20, 2018
  7. Audiofreak1

    Audiofreak1

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    Sep 20, 2018
    Hey venom you would not know where I can get ahold of zener diodes rd8.2js-t1
     
  8. VenomBallistics

    VenomBallistics

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    Aug 30, 2018
    zener diodes are interesting devices in that they are often labeled according to rating. it should read 8.2V across it in action. if not, search according to voltage for a replacement
     
  9. Audiofreak1

    Audiofreak1

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    Sep 20, 2018
    Well I tested all the zener diodes and there fine. One side is a touch higher on the reading but good to go. Now the power transistor 613 is reading different from 614 this might be the culprit so I am ordering 2 of them one for each side. I will update after I receive parts and replace. Thanks for all the help so far greatly appreciated
     
  10. VenomBallistics

    VenomBallistics

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    Aug 30, 2018
    when you say 613 and 614 are reading differently what are you measuring? Resistance? Voltage?
    Kinda important as you stated in a previous episode of the amp saga that you had to crank what looks like VR604.
    Yeah that will swing voltage.
     
    Audiofreak1 likes this.
  11. Audiofreak1

    Audiofreak1

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    2
    Sep 20, 2018
    I mean q613 and q614 they read different I ordered them and I will replace both. As far as the zener diode I feel like a idiot read the numbers on the board wrong they were resisters. There all fine I pulled them to read and there good to go. I will check the zener diode you said tonight. And you or whoever said you pay a lot and get a little. Zener diodes are 5 a pice
     
  12. VenomBallistics

    VenomBallistics

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    Aug 30, 2018
    Zeners are used for voltage regulation. you can put 100V across them and it'll read rated voltage ... in your case 8.2.
    this also lends itself as a protection device ... If we know voltage over say .. 12V will bork the bork, and we anticipate needing only say .. 5V in operation, the 8.2V stone wall will save the component ... I see some of them being used in this way in your amp. D602 and D604 are examples of this. they protect the differential input FET gates from static and some degree of human error.
    calm down ... we're out to find why its got its pronounced startup offset.
     
    Audiofreak1 likes this.
  13. Audiofreak1

    Audiofreak1

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    Sep 20, 2018
    F36502A9-B1F4-4734-836A-006EFA8E0AA3.jpeg
    Yeah it just weird the right side is 3.87 on the dc offset. I got the left side working. I am not positive but I think q613 was a cold soilder or the source might have had a bad connection. Either way left side is all normal again sounds better with those new caps from what I hear. New power caps and amp board got new caps. I was just listing to the amp floor of the left side and I notice a slight hum from about 4 feet away. My guess is it’s something on the right side making it. Cause when I turn it up with nothing playing you can hear the fuzz in the back ground get louder not bad loud. Well q614 might be the culprit we will see here I will let the amp drain overnight and soilder q614 with fresh soilder and try it to see if that one has cold soilder too looks like it might. As far as the zener diodes I check most on left they were good still. Did not pull right side out yet. Waiting till I check and solder q614. Then to the zener on the right. Also right side not getting as hot anymore.
     
    Last edited: Oct 18, 2018
  14. VenomBallistics

    VenomBallistics

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    Aug 30, 2018
    You might have mentioned it and I missed it ... did the right side ever work in your testing?
    I know it sucked the driver in hard at start up and gradually released ... did it function after it "sobered up"?
     
    Audiofreak1 likes this.
  15. Audiofreak1

    Audiofreak1

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    Sep 20, 2018
    No it never sobers up stays in it drunkin state. It plays at over a quarter volume very staticky and only when it gets to loud parts. The louder I turn it the more static and some music audible in the speaker. I am going to head to workshop here in a bit to get this q614 re soldered and tested. It’s a 3.3 watt n channel mosfet. We will see. Just wanted to say thanks again for your help and continuing help:)

    Oh and I just remembered that the right side was the side I hooked up the bridge wrong :( so dead components are there. I resldered the n channel and now no sound from that side still got the low hum
     
    Last edited: Oct 18, 2018
  16. Audiofreak1

    Audiofreak1

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    Sep 20, 2018
    I checked all of them there fine but you know how the mind is. Always thinking.

    I want cookies :)
     
  17. VenomBallistics

    VenomBallistics

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    Aug 30, 2018
    I'm starting to get the vibe that you're kinda new to this sort of thing, but versed enough to try.
    C614 and C618 are DC blockers so the front end can be devastated and not cause an offset, so we need not look in front of those caps ... yet.
    That means we can work from there toward output till its stable.
    This design makes a lot of use of MOSFETs.
    MOSFET and CMOS devices are the most sensitive to damage by ESD You would be wise to figure out a way to ground yourself as you handle these things.
    Also, all semiconductors are susceptible to damage from overheat. find some kind of tools to clamp the leads (hemostats are common) so that they can take up the heat while you solder.
    I just have this feeling that your borking good parts on your way through as acts taken seem to have been detrimental.
     
    Audiofreak1 likes this.
  18. Audiofreak1

    Audiofreak1

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    Sep 20, 2018
    Yes I am new to electronics repairing. I should have known better I used to build and repair computers and I have a lot of electrical experience. We always wore a wrist band grounded to the unit. And I had that feeling too. I am being as cautious as I can. Like I said I am new to repairing boards trying to learn as much as I can in this area of expertise. I will check in front of c614 and c618 tonight. I need to get a scope and a dc power supply test unit also. I set a goal for myself to learn this field of study. Should have done this along time ago when I was younger just never knew I enjoyed it as much as I do. Love a challenge
     
  19. VenomBallistics

    VenomBallistics

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    Aug 30, 2018
    yup ... thought something along those lines.
    In this field, it helps to visualize how things are supposed to work.
    Transistors, MOSFET or BJT have a set of specs where they are completely on, and completely off. known as saturation and cut off.
    That whole line of transistors Q608, Q610, Q612 and Q614 work with all the associated passives in that line across to hold the output transistors exactly at cutoff with no signal applied.
    You need to get them doing that again before we even start to look to the left of the aforementioned capacitors ... stuff over there can be fried without having any effect on the sections we are looking at.
    So logically, it is best to resolve this sections issues before we evaluate any damage that may have occurred to the left of those DC blocking capacitors.
     
  20. Audiofreak1

    Audiofreak1

    32
    2
    Sep 20, 2018
    Ok I got the right side working replaced two zener diodes. Bios and offset is normal. Now the left side produces a loud hum at about 120 hz and I am getting 31.9v ac out of the left channel. Right channel is working ok now. I have no idea why it keeps going back and forth to channels. But I am sure it has something to do with the rails. Maybe the fets are bad. I want to test the power board first then test the right channel to see if I can find it. Any suggestions? I am going to look to buy a scope also.
     
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