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Help with amp repair
Help with amp repair
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Old 27th May 2009, 02:37 AM   #1
yobobrox is offline yobobrox  United States
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Join Date: May 2009
Default Help with amp repair

Alright, I've been lurking here for a few months trying to figure out what to do with my damaged Kicker KX700.5 and I've finally caved in and registered so I can ask for some help. I've read over a lot of Perry Babin's site, and I've read a lot of posts, but I'm not sure what to do next...

My amp was attacked by rainwater that leaked into my trunk somehow. Now, it's stuck in protection mode. So, I pulled it open and found (what I think is) a FET that was highly corroded, along with a few tiny resistors. Nothing else appears to be affected. I cleaned the corrosion off with acetone and alcohol. Then, I tried powering up the amp without any speakers attached and it still went straight to protection mode. I have a DMM, and I tried testing some FETs and resistors, but got pretty mixed up and wasn't sure if I was even identifying FETs properly. I'm hoping someone here can give me some tips on what to do....it's a bit overwhelming.

Thanks
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Old 27th May 2009, 07:35 AM   #2
Perry Babin is offline Perry Babin  United States
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Location: Louisiana
Can you send me a few photos off the damaged area and one showing the overall layout?

babin_perry@yahoo.com
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Old 27th May 2009, 03:22 PM   #3
yobobrox is offline yobobrox  United States
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Absolutely; coming up within an hour.
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Old 27th May 2009, 06:28 PM   #4
Perry Babin is offline Perry Babin  United States
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When checking the power transistors (those mounted to the heatsink), you should not read anything near 0 ohms between the legs of any individual transistor. Did you have any that read near 0 ohms?
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Old 28th May 2009, 03:45 AM   #5
yobobrox is offline yobobrox  United States
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Ah, ok. That was where I was getting confused. I wasn't sure if polarity of the meter mattered or if I was supposed to be testing between all the legs (giving 3 combinations to test for a 3 legged part).

Alright, I tested them again and found around 5 that read ~0 ohms. I'm going to try more cleaning of the board around them (one is on the bottom row of transistors, and the others are on the top row), but I imagine that they are toasted. If so, I just read the numbers off the part and purchase replacements? Where do I purchase replacements? And do they all have to be the same batch? I read something about problems between batches, but I didn't understand it all.
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Old 28th May 2009, 08:14 AM   #6
Perry Babin is offline Perry Babin  United States
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Location: Louisiana
What are the numbers on the ones that appear shorted.
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Old 28th May 2009, 12:03 PM   #7
yobobrox is offline yobobrox  United States
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I said that backwards - one is on the top of the board and the rest are on the bottom. I can point them out in pictures if needed.
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Old 28th May 2009, 12:14 PM   #8
Perry Babin is offline Perry Babin  United States
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Location: Louisiana
What are the numbers on the ones that appear shorted.
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Old 28th May 2009, 08:52 PM   #9
yobobrox is offline yobobrox  United States
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Hmm, I can't figure out what the deal is, but I got different readings on several of the transistors today (checked out OK today). Anyway, I desoldered 4 of them that all read zero ohms across the two outside legs. The part numbers are:

Top Row, 5th from right:
YG225N2
(NPN diagram)
35

Top Row, 6th from right:
YG225C2
(PNP diagram)
35

Bottom Row, 5th from right:
YG225N2
(NPN diagram)
35

Bottom Row, 6th from right:
YG225C2
(PNP diagram)
35
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Old 28th May 2009, 08:57 PM   #10
Perry Babin is offline Perry Babin  United States
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Location: Louisiana
Those are the rectifiers. The outer legs are shorted by the transformer windings when they're in the board. That's normal.

Are any others shorted?
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