r 151 accent resistor burns

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  • gihaume
    Posts 298
    Joined: May 12th, '14, 14:48

    As stated in the thread VCA accent troubles, we are 2 people to have this same problem, and at least me without any other unfindable mistake (yes only another one but I know why).

    I also checked many times a lot of things, so much that with all the movements, I broke the "Cable 10Pos" linking both PCBs! I checked every component's place and way, resistors values, and transistor's proper functioning of the accent section.
  • User avatar
    e-licktronic Site Admin
    Posts 519
    Joined: Feb 16th, '11, 13:36

    Dear Diyer,

    R151 burned because you get a short cut between ground and +15v psu rail.
    C34, Q27 or the 4011 could be the problem.

    Best regards,
    e-licktronic
    Best regards,
    e-licktronic
  • keen
    Posts 7
    Joined: Jan 13th, '14, 06:27

    Hello franzkleid,

    I had same problem on 4th batch kit.
    Please try unbuffered 4011UB.
    I solved R151 problem by it.

    cheers
  • gihaume
    Posts 298
    Joined: May 12th, '14, 14:48

    Thank you!

    The batch before the 4th did have a different 4011 than BE?
  • zmb
    Posts 21
    Joined: Feb 28th, '14, 23:07

    keen wrote:Hello franzkleid,

    I had same problem on 4th batch kit.
    Please try unbuffered 4011UB.
    I solved R151 problem by it.

    cheers
    wow is that really the issue? My local electronics retailers don't seem to differentiate, just listing "4011" without any suffix. I guess I could go in-person or call to verify the buffered vs unbuffered versions...

    EDIT: I just checked the TR-808 service manual and as far as I can tell they used 4011B type NAND gates. So maybe that's not the problem?
    Attached screenshot from the service manual:
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  • keen
    Posts 7
    Joined: Jan 13th, '14, 06:27

    Hello.

    Sorry, I'm not sure why UB version solved it.
    I have 2 kits of 4th batch. Both kits had same problem. And solved it with 4011UB.
    BTW, 4011UB is used for 9090 too.

    regards,
  • krisbo
    Posts 33
    Joined: Apr 23rd, '14, 09:12

    Replace your 4011. I replaced mine with a 4011BE and it's rocking now!
  • gihaume
    Posts 298
    Joined: May 12th, '14, 14:48

    I also have a few yocto kits so I tried with the 4011BE of another kit (not built yet), and again the same problem!
  • krisbo
    Posts 33
    Joined: Apr 23rd, '14, 09:12

    By the sound of it there may be some issues with the 4011 used seeing as a fewguys have had issues with them. Pick yourself up a new one from an electronics shop and see how you go.
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