Okay so i finally found the problem. It is coming from the output of the amp.. Looks like the output is not reaching fast enough 0V.. and that is triggering some sort of protection. I desoldered r577 and r578 one by one checking if the amp would start after each being desoldered. After i desoldered R578(leaving R577 in place) the amp would load up my lab supply(which is only capable of 5A..) which entered in Constant current mode, reaching its current limit then the amp would immediateley enter in protection mode, not powering up. But then i desoldered R577 and put R578 in place and tried powering the amp on, which well did nothing, didnt even try.. (like with R577 in place and R577 out of the circuit).. At this point i am not sure how to continue the repair.. Any ideeas?
Thanks again!
Thanks again!
Okay so, even closer, only once channel is bad, the other one actually works fine(R577 in place). Now i have no ideea where to search the problem, any tips for me?
i only tested it with bass so im not sure about highs but it sounds clear and it has the power... ihave to set the bias current which i cant set based on the instructions given in the service manual.. If the bias is not set correctly i cant really wait a clear audio output..
Okay, so interesting stuff, when i turn on the amp, the voltage gets offset. Between the input ground and(at the B-(GND)) the components of the amp except the finals. So where id usually measure +45V in the protection circuits etc ill measure +52V... Also measuring the supply voltage on the finals will be like -36V and +52V, but not if i measure compared to the DC-DC converters ground(TP1 and TP3) then the voltage is okay, +-45V. Also when the ground is offset if i switch the amp in Low impedance mode it would instantly cut out and it wont restart until i put it back to lowZ mode
If you connect the input RCA shield ground to the main ground, does the amp still go into protect mode (or have the offset issue)?
Okay so connecting the ground of the input jack to the ground of the supply fixes the thing totally, like iv put back the 12kohm resistor which is between output and speaker protection and now the thing pwoers up normally, ground is not shifted and my low impedance problem is solved too.. But what is the cause? I mean is this the permanent fix now?
Some alpine amps sense and indicate that the shield ground is open. Those amps look for a ground on the shield (normal head units have a grounded shield). I've never seen an amp that wouldn't power up without a grounded shield. I doubt that it's normal but it would have likely worked from the start if installed with a normal head unit.
Whaaat, that is crazy! But the joke is that the speaker protection circuit would not let the amp start, because of this thing.. Kinda crazy to me.. It might turn out it still has some problems but i will see when loading it properly with like a 2 ohm load or something. I have one last question, can you please tell me how to set the bias current on this?
Also it seems like it does not have a low voltage protection, i can drop the voltage way way down to like 8-9 volts where it starts clipping but still works.. is that normal? Shouldnt it stop earlier?
Also since we are here, have yo ugot any ideea what is the normal idle current for this amp? Its drawing like 1A with the biases on the minimum
Okay so i think i might have found the problem. There is a c109 cap which should connect the two grounds together but that cap is not 100pf its 1200pf, that might be the problem i think
It is mistaken, you cant set it based on that.. But i figured it out anyways. You have got to measure between the source of the finals and the 0.1ohm resistors 🙂
- Status
- Not open for further replies.