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

sndtch6 · 10th April 2004, 09:12 PM

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 · 10th April 2004, 10:26 PM

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 · 10th April 2004, 10:55 PM

Hi,

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

I think it's propably transistors shorted

sndtch6 · 10th April 2004, 11:13 PM

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 · 11th April 2004, 12:06 AM

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 · 11th April 2004, 03:27 AM

Quote:

Originally posted by 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?

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 · 11th April 2004, 03:29 AM

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

sndtch6 · 11th April 2004, 03:30 AM

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

sss · 11th April 2004, 10:47 AM

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

HDTVman · 11th April 2004, 01:41 PM

Quote:

Originally posted by sndtch6
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

10th April 2004, 09:12 PM	#1
sndtch6 diyAudio Member Join Date: Apr 2004 Location: california	car amp repair question!!!!!!!! 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?

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10th April 2004, 10:26 PM	#2
sss diyAudio Member Join Date: Jul 2003 Location: Israel , haifa	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

10th April 2004, 10:55 PM	#3
ddog diyAudio Member Join Date: Oct 2003 Location: Finland	Hi, look for shorts in PSU part, switcher transistors, transformer, caps etc. I think it's propably transistors shorted

10th April 2004, 11:13 PM	#4
sndtch6 diyAudio Member Join Date: Apr 2004 Location: california	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?

11th April 2004, 12:06 AM	#5
Eva diyAudio Member Join Date: Oct 2003 Location: Near the sea	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]

11th April 2004, 03:29 AM	#7
sndtch6 diyAudio Member Join Date: Apr 2004 Location: california	thats the thing though is that there is no brown marks or any visual confirmation that anything is blown up of dead

11th April 2004, 03:30 AM	#8
sndtch6 diyAudio Member Join Date: Apr 2004 Location: california	added note, how would i check the transistors to see if they are bad?

11th April 2004, 10:47 AM	#9
sss diyAudio Member Join Date: Jul 2003 Location: Israel , haifa	if u got a multimetter theres an option to check diodes the transistor is like 2 diodes NPN- negative - positive - negative

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