car amp repair question!!!!!!!!

[sndtch6]

i am new to this but i have an amp that i am trying to fix and is bugging the heck out of me. it is a Alpine FLEX MRP-F356 amp. 4 ch @ 75W and a sub @ 150W. the problem is that when i hook it up to my car it keeps blowing my fuse now so i hooked it up to a 12v psu in my house, everything connected except the remote. looks fine untill i connect the remote and it draws so much power that my Psu over heats. i checked it and it is going from 12 v to 5 v with a half second delay. it looks like the power supply in the amp. maybe a deac Cap. can any one help me with this?

 

[sss]

if u are not experienced then fixing car amps will be very difficult to u, anyways dont do those test with the power supply when no fuses connected , probably all amps psu transistors allready dead

 

[ddog]

Hi,

look for shorts in PSU part, switcher transistors, transformer, caps etc.

I think it's propably transistors shorted

 

[sndtch6]

thanks for telling me that. i didn't even think of the transistors shorting.

also is there a schematic on this model that is public domain, if not it's ok?

 

[Eva]

Most common causes of that are :

- Shorted transistor(s) in the audio output stages [most usual cause]

- Control circuit of the PSU malfunctioning and causing heavy cross-conduction or transformer saturation [rare]

- Shorted rectifiers in PSU transformer secondary [very rare]

 

[dkemppai]

i am new to this but i have an amp that i am trying to fix and is bugging the heck out of me. it is a Alpine FLEX MRP-F356 amp. 4 ch @ 75W and a sub @ 150W. the problem is that when i hook it up to my car it keeps blowing my fuse now so i hooked it up to a 12v psu in my house, everything connected except the remote. looks fine untill i connect the remote and it draws so much power that my Psu over heats. i checked it and it is going from 12 v to 5 v with a half second delay. it looks like the power supply in the amp. maybe a deac Cap. can any one help me with this?

From what you describe, it makes me think that your output transistors are blown. Possibly (but rarely) the rectifier diodes. Chances are if you open it up, you'll see what's blown. If any of the output transistors are blown in the audio section, I'd recomend replacing them all... ...same goes for power supply tranistors...

-Dan

 

[sndtch6]

thats the thing though is that there is no brown marks or any visual confirmation that anything is blown up of dead

 

[sndtch6]

added note, how would i check the transistors to see if they are bad?

 

[sss]

if u got a multimetter theres an option to check diodes
the transistor is like 2 diodes
NPN- negative - positive - negative

 

[HDTVman]

thats the thing though is that there is no brown marks or any visual confirmation that anything is blown up of dead

blown power transistors don't show any external marks unless they are plastic case type. these can have the top poped off if they fail violently.

later BZ

 

[Eva]

The most common pinout of the bipolar power transistors used on these kind of amps is :

[Device seen from marking side and with legs pointing down]

Base - Collector - Emitter [from left to right]

Most common fault is a short between collector and emitter. Some devices may appear to be almost shorted due to the circuit showing a low impedance path, in that case try testing the devices removed from the circuit