Disaster
Hi people, I am in urgent need of help before going mad!
This is the amp I’ve just made and it took me a whole week to do it and managed to make it working perfectly.
( http://www.ampslab.com/c300.htm )
I wasn’t so lucky the second time I hooked it up because as pumping up some music, the center tap wire (ground of amp) went loose and the thing just freaked out!
I switched of immediately and rehooked the ground properly, however only a loud buzzing sound was heard! A disaster!
Checked out the components, no components were carbonized.
Checked out two power transistors any hfe resulted to be fine (aprox150)
As a start I’m thinking of replacing all small power bjt transistors.
I’m not an expert in troubleshooting, PLS what is your opinion about the problem
Here below is a schematic of the amp with grounds illustrated with red boxes
Hi people, I am in urgent need of help before going mad!
This is the amp I’ve just made and it took me a whole week to do it and managed to make it working perfectly.
( http://www.ampslab.com/c300.htm )
I wasn’t so lucky the second time I hooked it up because as pumping up some music, the center tap wire (ground of amp) went loose and the thing just freaked out!
I switched of immediately and rehooked the ground properly, however only a loud buzzing sound was heard! A disaster!
Checked out the components, no components were carbonized.
Checked out two power transistors any hfe resulted to be fine (aprox150)
As a start I’m thinking of replacing all small power bjt transistors.
I’m not an expert in troubleshooting, PLS what is your opinion about the problem
Here below is a schematic of the amp with grounds illustrated with red boxes
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Keep in mind that a transistor that measures a normal hfe,
may be damaged (it has happened to me). Your desicion to replace small transistors is quite reasonable, as they are more commonly damaged in such situations. In a situation like this, where I couldn't find a solution, I simulated the whole thing, found voltages in different places in the simulator, and compared them with real life. Wrong voltages existed around a small signal transistor (previously measured with a normal hfe). When I replaced it everything was ok.
I am not a repairer professionally, so this approach may be wrong. It's just what I did. Anyone else with more experience please contribute. It may be even a passive component (capacitor perhaps), which would be very unfortunate, because I thing it will be much more difficult to find it.
may be damaged (it has happened to me). Your desicion to replace small transistors is quite reasonable, as they are more commonly damaged in such situations. In a situation like this, where I couldn't find a solution, I simulated the whole thing, found voltages in different places in the simulator, and compared them with real life. Wrong voltages existed around a small signal transistor (previously measured with a normal hfe). When I replaced it everything was ok.
I am not a repairer professionally, so this approach may be wrong. It's just what I did. Anyone else with more experience please contribute. It may be even a passive component (capacitor perhaps), which would be very unfortunate, because I thing it will be much more difficult to find it.
jaycee said:Q8 and Q10 form an EF VAS. Q9 is a safety cutoff, when the VI limiter activates it can result in Q10 being saturated. Q9 detects this and cuts the base current.
Leach explains this for his own amplifer here
Yes and no :collector of Q9 must go to base of Q8, R18 should be zero!
Supply voltages seem to be fine.
+/- 72v before accident (without amp connected)
+/-70v after accedent (without amp connected)
dont know why this 2 volts drop, maybe filter electrolytycs had a hard time during the accident.
Do you think driving transistors have been damaged ? because I have 10 of them and they are quite costy. how can I check if the are fine or not ?
+/- 72v before accident (without amp connected)
+/-70v after accedent (without amp connected)
dont know why this 2 volts drop, maybe filter electrolytycs had a hard time during the accident.
Do you think driving transistors have been damaged ? because I have 10 of them and they are quite costy. how can I check if the are fine or not ?
replaced all bjt transistors from the line shown back, amny of them seemed to be faulth after hfe check, however still somthing wrong !
Now i`m going to replace Q10 and Q12
Do you think that the new replaced components cab be destroyed in the falty circuit
Now i`m going to replace Q10 and Q12
Do you think that the new replaced components cab be destroyed in the falty circuit
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