Vasquez Rich Posted March 29, 2008 Share Posted March 29, 2008 A mate of mine had this combo left in his rehearsal room and the owner don't want it, he's a drummer so he's thrown it at me. It has a loud, and I mean loud, buzz from the speaker when it's powered up. The speaker is fine when connected to my Harke so is in decent nick. There was a loose end of a jack plug tip stuck in the high Z input, and I have removed this.. the input section appears fine and the meter thing these Ashdowns have on them responds OK to a bass played into either input. I think the issue may well be in the power section as there is a 2.1V appearing at the speaker out jack (tip of the jack) that I an sure shouldn't be there. The input and output potentiometers have no effect on this. I am OK with electronics and soldering so if I have a clue as to which components are bust or need replacing then I can do that, just need some help in either finding the problem parts or finding out how to find them. Thanks, Richard Quote Link to comment Share on other sites More sharing options...
Vasquez Rich Posted March 29, 2008 Author Share Posted March 29, 2008 I've just stripped the power stage out and one of the large electrolytic capacitors (4700 microfarad, 100V) has one of it's connections loose. In addition it looks like something has got it hot enough to melt the solder connection leaving the metal strip loose through the circuit board, there are some small black "burn" marks on the underside of the circuit board, but only around where the solder should have been. I can obviously resolder this back, but was wondering if the connection has got hot enough then is it likely that the capacitor has blown? What could get that connection so hot? Richard Quote Link to comment Share on other sites More sharing options...
DHA Posted March 29, 2008 Share Posted March 29, 2008 [quote name='Vasquez Rich' post='165981' date='Mar 29 2008, 05:45 PM']I've just stripped the power stage out and one of the large electrolytic capacitors (4700 microfarad, 100V) has one of it's connections loose. In addition it looks like something has got it hot enough to melt the solder connection leaving the metal strip loose through the circuit board, there are some small black "burn" marks on the underside of the circuit board, but only around where the solder should have been. I can obviously resolder this back, but was wondering if the connection has got hot enough then is it likely that the capacitor has blown? What could get that connection so hot? Richard[/quote] Looks like some DC has got on to the speaker connection. This will be due to a power supply fault and the current drawn will have caused the burning on the board. I expect there was a low ohm resistor between the pre-amp and power section grounds as this stops earth loops. But when there is a problem this resistor will overheat. Beware - this sort of fault will burn out speakers if the DC flowing gets to large. I would say that there is a fault in the power section and the other damage you are seeing is an effect of this and maybe not the cause. This needs to be looked at by someone that has the diagrams and the knowhow to fix it IMHO. Dave Quote Link to comment Share on other sites More sharing options...
Vasquez Rich Posted March 29, 2008 Author Share Posted March 29, 2008 Dave, Thanks for that. I re soldered the capacitor connection as it was on a direct run on the circuit board to the point at which I was getting the DC on the speaker out terminal. I rebuilt everything up and it seems to be working, there is no voltage at the speaker terminal and the speaker itself sounds normal with just the normal hissing when it's turned up. I take your point about having probably repaired a result of a fault and not the fault itself.. I will test the thing out properly in the next few days. If I keep it it will be my 3rd best amp in anycase. If the fault returns then it will be a dead giveaway with the loud buzzing. Thanks again, Richard Quote Link to comment Share on other sites More sharing options...
DHA Posted March 29, 2008 Share Posted March 29, 2008 [quote name='Vasquez Rich' post='166134' date='Mar 29 2008, 09:52 PM']Dave, Thanks for that. I re soldered the capacitor connection as it was on a direct run on the circuit board to the point at which I was getting the DC on the speaker out terminal. I rebuilt everything up and it seems to be working, there is no voltage at the speaker terminal and the speaker itself sounds normal with just the normal hissing when it's turned up. I take your point about having probably repaired a result of a fault and not the fault itself.. I will test the thing out properly in the next few days. If I keep it it will be my 3rd best amp in anycase. If the fault returns then it will be a dead giveaway with the loud buzzing. Thanks again, Richard[/quote] Hi Richard, sounds like you got a good result. Might just have been the connection to the cap that caused the problem. Dave Quote Link to comment Share on other sites More sharing options...
Vasquez Rich Posted March 30, 2008 Author Share Posted March 30, 2008 Yes, it may have been dodgy soldering leading to a bit of heat build up, maybe a small bit of arcing.. anyway will test it and let you know. Thanks, Richard Quote Link to comment Share on other sites More sharing options...
Vasquez Rich Posted April 5, 2008 Author Share Posted April 5, 2008 Had it switched on for 4 hours and no ill effects. Looking good. Will give it a good run at a rehearsal next week. Richard Quote Link to comment Share on other sites More sharing options...
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