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Old 9th August 2011, 03:49 AM   #1
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Default Please help me repair this amp.

Hi Everyone,

I was given an Altec Lansing inMotion IM7 a while back and I accidentally shorted the built in subwoofer amp. One of the IRF7379 chips caught fire and two other small components were also damaged. I replaced the 7379 chip and the amplifier was partially working but the sound was very "muddy" and there was a constant crackling noise. I removed the other two damaged components entirely and the sound quality improved, most of the crackles went away but the sound is still not very clear. The problem is that I have no idea what to use to replace the two small components (outlined in the picture below) The upper one reads "KA2" and the lower reads "Z 2".

Click the image to open in full size.

I haven't been able to find anything other than that they are bipolar junction transistors. Does anyone know of a suitable replacement for these? Everything works perfectly, including the amps for the two main speakers, except for the sub amp. Thanks in advance!
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Old 9th August 2011, 05:39 AM   #2
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KA2 could be a diode, replace with 4148
Z 2 may be a zener, measure the voltage from a working circuit...
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Old 9th August 2011, 05:48 AM   #3
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Hi,
Did you check closely the Q9 and D20. It is look like burned out or something happened in there. The Q9 chip is close to L6 or next capacitor C58 or 50. I can not read the number right. Do you have an schematic?
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Old 9th August 2011, 05:24 PM   #4
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Thanks for the help!

The Q9 chip is an IRF7379, it looks messed up because I replaced it. When the original one burned, it damaged two of the solder pads (upper left) and they came off. I had to improvise to make the connections.

I decided that since it didn't work anyway that I would take the KA2 and Z 2 parts from elsewhere on the board (I took them from the left channel), and the sub still doesn't work properly. It sounds great when turned down low but when the volume is turned up it is very distorted and muddy. I guess that other components were damaged also. I don't know a whole lot about this sort of thing so is there any other components I could check or is this board pretty much dead? Thanks!
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Old 12th August 2011, 11:08 PM   #5
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Use for the headline this:
Altec Lansing inMotion IM7 - damaging IRF7379 and file this topic about "class-D"
Then you will receive much more advices.
http://datasheet.octopart.com/IRF737...heet-55827.pdf
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File Type: jpg Altec Lansing inMotion IM7 front.jpg (67.4 KB, 55 views)

Last edited by tiefbassuebertr; 12th August 2011 at 11:13 PM.
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