Hi all
I bought a pait of Aleph 3 boards from Kristijian a while back, put the amp together and everything was working great until today :-( one of the channels just died. The LED does not come on and initially I thought there might be a problem with the connections - I tried wriggling the speaker connections and I saw sparks at the speaker connector!
At this point I disconnected all the inputs and outputs and examined the boards. Nothing seems to be fried, all resistors look ok. Does anyone have any thoughts on where I should start from?
I checked the power supply circuit and that part seems just fine. If I look at the circuit (link below) it looks certain that the 244 device on the top right hand corner closest to the LED has blown, any thoughts?
http://web.vip.hr/pcb-design.vip/aleph-3.html
thanks in advance
vsr
I bought a pait of Aleph 3 boards from Kristijian a while back, put the amp together and everything was working great until today :-( one of the channels just died. The LED does not come on and initially I thought there might be a problem with the connections - I tried wriggling the speaker connections and I saw sparks at the speaker connector!
At this point I disconnected all the inputs and outputs and examined the boards. Nothing seems to be fried, all resistors look ok. Does anyone have any thoughts on where I should start from?
I checked the power supply circuit and that part seems just fine. If I look at the circuit (link below) it looks certain that the 244 device on the top right hand corner closest to the LED has blown, any thoughts?
http://web.vip.hr/pcb-design.vip/aleph-3.html
thanks in advance
vsr
Hi!
Although having never built an Aleph so far, I think that most of the time the integrated devices (transistors, diodes) are the cause for a fault, so check first the power transistors, then the drivers.
But a fault in power transistors can also cause the emitter resistors to blow (the 0.47 ohms), so you might check them, as well.
And always check devices unsoldered from the circuit, since connection to other devices changes the values you get while measuring...
And look for the reason why a specific device has blown... too much heat? bad solder joint? Short with probes (unlikely in your case, but my #1 cause for failure
)? Or bad luck...?
Bye,
Arndt
Although having never built an Aleph so far, I think that most of the time the integrated devices (transistors, diodes) are the cause for a fault, so check first the power transistors, then the drivers.
But a fault in power transistors can also cause the emitter resistors to blow (the 0.47 ohms), so you might check them, as well.
And always check devices unsoldered from the circuit, since connection to other devices changes the values you get while measuring...
And look for the reason why a specific device has blown... too much heat? bad solder joint? Short with probes (unlikely in your case, but my #1 cause for failure
)? Or bad luck...? Bye,
Arndt
Hi vsrvsr123 said:
Assuming you have a DMM, you should provide some more details about the voltages you have on the critical points in the circuit.
What do you measure at the output? DC? How much?
What voltage between emitter and collector of the MPSA18 of the current source?
What voltage over the source resistors and so on.
The link you provide is a nice schematic, but for more in dept measurements the PDF at Passlabs is better IMHO.
Keep us informed and (small but important warning) : Discharge the big cans properly before poking around with the soldering iron :nod;
/Hugo
First thing to do is measure the fets.
You will have to take them out to measure accurately.
Here's a good link to know how to measure them:
http://www.eatel.net/~amptech/elecdisc/ampfail.htm
Start with the diff-pair then work yourself trough the outputs.
You can always compare measured values with the good working side.
Check the zeners as well.
/Hugo
You will have to take them out to measure accurately.
Here's a good link to know how to measure them:
http://www.eatel.net/~amptech/elecdisc/ampfail.htm
Start with the diff-pair then work yourself trough the outputs.
You can always compare measured values with the good working side.
Check the zeners as well.
/Hugo
Banned
Joined 2002
Banned
Joined 2002
MPSA18
Hi
Sorry, the MPSA 18 I was referring to is the one on the top of the circuit.
I will take the measurement across the 390 ohm later and post it here.
As for why I didnt number the components, I did not draft the figure, its from Kristijan's web site, the Aleph 3 service manual at www.passdiy.com also has the same circuit and the MPSA 18 I was referring to is labelled as Q105.
thanks
vsr
Hi
Sorry, the MPSA 18 I was referring to is the one on the top of the circuit.
I will take the measurement across the 390 ohm later and post it here.
As for why I didnt number the components, I did not draft the figure, its from Kristijan's web site, the Aleph 3 service manual at www.passdiy.com also has the same circuit and the MPSA 18 I was referring to is labelled as Q105.
thanks
vsr
Banned
Joined 2002
With pleasure and thanks to Nelson and Passlabs we got the whole series of Alephs here: http://www.passlabs.com/aleph.htmJasonL said:
To answer your second question: I don't know, but I guess it should be possible.
A variac should make life easier IMO. Nothing to disconnect.
/Hugo
Banned
Joined 2002
What i ment was not to power the aleph's up with the out-puts attached to the main board. i am not Rich and cant afford to rune all my fets. not that i have but i take lots of practice in being care full. ill get a nice var-iac and power it up slowly also. just want to be care full and take it one step at a time.
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