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1979 Combo 300 problem

Discussion in 'Amps and Cabs [BG]' started by cmccaig, Aug 11, 2005.


  1. cmccaig

    cmccaig

    Aug 11, 2005
    Hey guys. new member and first thread. woohoo. i have a pretty annoying problem. when i play my amp, the volume cuts down to about 1/5, or more, of the actual output or it starts to sound like you are trying to plug your cord in and can't find the hole. it is very loud. i have found that playing with the pre-gain button a little bit will usually fix the problem, but only for a very short while. so my question to you gurus is, does the head need cleaning or is it something more serious. it is very annoying and makes for a very difficult time trying to practice, and there is noooooooo way to play live with it doing that. any and all help would be greatly appreciated. thx. i await your repies.

    chris :bassist: :confused: :help:
     
  2. Chef

    Chef Moderator Staff Member Supporting Member

    May 23, 2004
    Columbia MO
    Staff Reviewer; Bass Gear Magazine
    Yeah, BTDT. Here's the thing:
    The IC chips on the circuit board are hung *upsidedown*

    So...over time, they vibrate loose. Pull the amp out and re-seat the chips and you'll be good for a while again. Seems like very time I re-seated the chips it lasted shorter and shorter times til I finally just stuffed the old girl in a corner.

    Pretty decent rig, really.
     
  3. cmccaig

    cmccaig

    Aug 11, 2005
    so where are the ic chips. not very familiar with the electronic parts of amps. i know what a resistor and capacitor is, but that is about as far as it goes. lol but if that will fix it for a while then that is fine, hoping to get me a hartke kickback 12 soon. only 42 pounds and 120 watts but that is all i need, and the weight difference is a tremendous blessing.. :D :hyper:
     
  4. Chef

    Chef Moderator Staff Member Supporting Member

    May 23, 2004
    Columbia MO
    Staff Reviewer; Bass Gear Magazine
    Yep, she's a heavy one.

    The amp chassis is bolted into the combo from the top. Remove all those screws, disconnect the speaker wire, pull it out...the IC chps are like little rectangles with 12-16 legs on each side. You can get a little chip puller at radio shack or someplace. Pull them gnetly out, slide them gently back in. Careful:) The legs can bend...
     
  5. ras1983

    ras1983

    Dec 28, 2004
    Sydney, Australia
    I had the same problem, the high-gain input would buzz very loudly after a few minutes. i took it in to have the speaker reconed (because the suspension had collapsed) and had the guy look at the input. it turned out that IT WASN"T EARTHED!!!!!!!! :meh: :meh:

    So now i just use the low gain input (its plenty loud) and problem solved.
     
  6. ???
    The input jacks are usually grounded through the chassis. So if the jack is tight, it's grounded. If it's not grounded through the chassis, it'd have a ground wire going to it. If indeed "the input jack wasn't earthed" he should've been able to fix that in about 2 minutes....
     
  7. ras1983

    ras1983

    Dec 28, 2004
    Sydney, Australia
    Maybe he was wrong then.
     
  8. cmccaig

    cmccaig

    Aug 11, 2005
    I'm assuming the IC Chips are black. i have the head out but the black chips, if those are the correct ones, all feel secure and don't move.???????
     
  9. cmccaig

    cmccaig

    Aug 11, 2005
    any other suggestions as i am uncertain as to whether this worked or not because of my previous statement. I am thinking of taking it in to get it looked at but if i can save the money and do iot myself i would prefer to do that. thx.