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Thread: Help,Help, Gremlins attacked my B-52 Amp.

  1. #1
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    Help,Help, Gremlins attacked my B-52 Amp.

    I have a B-52 Stealth Series LG100a guitar Amplifier . The amp. had a humming feed back problem. I opened up the head case and searched for any obvious trouble, loose wires, bad grounds, burn and over heat conditions potentiometers, switches and plugs. When I plugged in the guitar and turned on the amp, there was a low output of sound. I checked all connections and cables all was good. I tapped on everything and nothing seemed to be intermittent (everything worked before I opened up the head case.
    I checked the resistance on all the switches,looked for any damage I may have done and everything looks okay.
    I can find no schematics or forum help for this B-52 head model. This is a LG 100a which is solid state not a tube amp. I can find plenty of information for the B-52 Tube amp.
    Can any one help me with this malfunction? I don't want to spend money on a service technician. I could fix this problem if I had the pr0per schematic and a suggestion on troubleshooting. I have no idea where to begin to find whats broke. No smells or obvious trouble that I have seen.
    I am a retired F-16 electrician, I have a decent repair shop in my basement. I would really appreciate any help or advice. e-mail [ ] [ telephone: 812-249-3823 ]
    Thank You,
    Dennis, Indiana U.S.A.

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    Last edited by bouttree; 01-27-2014 at 07:26 PM. Reason: add info

  2. #2
    Supporting Member The Dude's Avatar
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    Does the sound go away when you turn the volumes down? If so check solder on the input jack.

    Is the amp putting out DC voltage? Measure at the speaker terminals. If so, you have a problem in the amplifier section of the amp- shorted output devices or the like.

    Is the sound AC voltage? If so I'd check the solder connections on your filter caps and or check the caps themselves. Possibly one is bad.

    It's a start.

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  3. #3
    Old Timer soundguruman's Avatar
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    common things are oxidized jacks, which have internal switches,
    when the switches fail to close, the audio path is interrupted.
    try installing a patch cord between "send" and "return."
    If the jack switch fails to close, the patch cord can bypass the problem.

    Second is grounds on the circuit boards, which depend on screw posts.
    The screws holding the circuit board to the mounting posts are often used as ground conductors.
    If the post contacting the chassis oxidizes, the ground connection is intermittent or lost altogether.
    If the screw post contacting the circuit board oxidizes, the ground is lost.
    If the screws become loose, the ground to the circuit board is lost.
    These can be bypassed with soldered wires, which are then screwed to the chassis with ring terminals.
    This is a really common failure point in Chinese designed amplifiers, so look carefully.
    These type of grounds fail pretty predictably.

    The circuit board has tin plated tracks. Up against this track, is a steel screw post, sometimes aluminum, or plated brass.
    The screw posts are held to the board and the chassis by black powder coated screws....
    The dissimilar metals encourage oxide to form, between the contact points. Then the ground connection fails.

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  4. #4
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    Thanks, My grounds seem to be good,i haven't checked them all. The in and out jacks is interesting,I will check them out

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