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Old 7th February 2007, 08:38 AM   #1
Dan2 is offline Dan2  South Africa
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Default Problem with small car amp

i have a 4 channel car amp (200w pmpo) which i want to use for a small home theater system. it was working fine, then two channels stopped working (Rear left and rear right). i replaced 2 caps that were a bit swollen, watched a movie to test it and all 4 channels were working. the next day there was a really loud buzz on one channel. i checked the dc voltage across the channels - front left and right had a dc voltage of abt 0.01v but rear left and right were at close to 5 volts!!! nothing seems blown in the amp, so my only guess is the amp chip is busted. can anyone confirm this and give me a solution???
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Old 7th February 2007, 11:32 AM   #2
sek is offline sek  Germany
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From 5V output DC I wouldn't say the chip is busted. But without any information on what we're talking about...

200Wpmpo is one point to look at, for example. It likely means 20Wrms per channel. As you post this in the chipamps category, this order of magnitude would be reasonable. Why don't you post a schematic, a parts list or a picture. Or all of em.

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Old 7th February 2007, 11:54 AM   #3
impsick is offline impsick  United States
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what are you using to power this car amp indoors? maybe you over juiced it or aint giving it enough.
what kind of chip? maker of amp?
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Old 11th February 2007, 11:49 AM   #4
Dan2 is offline Dan2  South Africa
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its a sansui car amp - and it as about 20w rms. i have opened it up and there are two stereo amp chips. the one chip shows no dc on the output, the other shows about 5v, and that is the same chip that is giving me problems.

before i knew much about electronics, i had this amp in my room. i had a 12v transformer, diode rectifier and a 4700uF cap as my power supply, which pushed out about 17v dc (oops). thats why the caps in the amp were a little swollen (i think). now im just using an off-the-shelf 1A transformer which delivers just enough power. the wierd thing is it was working fine the first night i hooked it up, and the next day the channel was buzzing.

i don't have schematics for this amp, and the numbers on the chips have rubbed off, so thats a bit of a problem.

i checked the voltages of the pins on both chips - the only difference was the 5v on the output.
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Old 11th February 2007, 04:07 PM   #5
impsick is offline impsick  United States
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did you say you replaced the swollen caps? probably should if not.
post some pics up.
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Old 16th February 2007, 06:27 AM   #6
Dan2 is offline Dan2  South Africa
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still getting the pics - sorry

yes i replaced the caps. before i replaced the caps, i only had one stereo chip working, i replaced them, then both stereo chips were working fine. the caps are relatively big (2200uF,16v)
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Old 17th February 2007, 04:33 AM   #7
impsick is offline impsick  United States
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ok pics should help. but watch out if you have 16v caps and your using a 17v power supply. i'd put some 25v or 35v caps in there to be safe and longer life
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