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Old 15th August 2010, 03:43 PM   #1
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Default Another fried Kicker KX1200.1

Background - I have basic replacement experience, but very limited troubleshooting knowledge. I've replaced caps, convergence chips, repaired game consoles and have a collection of soldering irons in varying wattage to work on boards.

I've read Perry Babin's multiple answers to kx1200 threads and have a few questions regarding some smoked power supply FETs on this (red board) amp.

1) The amp appeared sealed and original, but the power FETs are 3205's with 100 ohm gate resistors (were they ever built with this combination?). Is it possible to run 3205's with this resistor or do they need to be changed to 47 ohm resistors? The resistors all read within tolerance.

2) If the resistors need to be changed, what is a good part number from Digikey? I tried crossing part number 660-RK73B2BTTDD470J that Perry Babin suggested, but came up blank. Using their search engine I found so many options that I got lost.

3) How can I check the gate drive transistors? They don't cost much to replace but I question my ability to not jack up the tighter/smaller soldering in that area.

Thanks!
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Old 15th August 2010, 07:52 PM   #2
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Still works great...
JBL BP 1200.1 Project
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Old 15th August 2010, 08:02 PM   #3
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The 3205's with the 100 ohm gate resistors are normal for this amp.
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Old 15th August 2010, 08:06 PM   #4
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I read through your thread and couldn't figure out what you were referencing from my questions. I do appreciate any help you can offer, though. Thanks.
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Old 15th August 2010, 08:13 PM   #5
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Quote:
Originally Posted by mike49504 View Post
The 3205's with the 100 ohm gate resistors are normal for this amp.
Okay, I wondered. The other posts about this amp suggested 'upgrading' the FETs to 3205's but needed the gate resistors to be changed out to 47 ohm. I assumed this meant someone had attempted a repair and botched the job.

On that note, do you believe the (within tolerance) resistors lead to a high probability of the gate drive transistors being okay, or would their condition be unrelated. I'll probably try to replace the transistors anyway, just trying to bump my chances of a successful repair.

THANKS!!! (for helping a newbie hack)
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Old 15th August 2010, 08:19 PM   #6
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The 100 ohm fate resistors are orginal . If they all test fine dont replace them.

If you switch to 47 ohm gate resistors you might have problems with the amp turning on to fast.

Your next question was how do you check the driver transistors for the power supply fets.

Set you meter to ohms and test between the legs of them 1-2 1-3 2-3

Post your results.
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Old 15th August 2010, 08:57 PM   #7
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Not sure if it matters, but these figures are with the bad FETs installed. (a repair shop wanted everything how I found it if I took it in, so I reinstalled them before I decided to attempt the repair myself.)

Q05:
1-2 = 11.1
1-3 = 29.6
2-3 = 37.4

Q11:
1-2 = 276.8
1-3 = 41.5
2-3 = 235.7

Sorry about the slow replies, I'm still a moderated poster so there is a bit of a delay.
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Old 15th August 2010, 09:14 PM   #8
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You can't tell much about the drivers with the defective power supply FETs in the circuit. If you're going to try to repair it yourself, you should remove the power supply FETs. If you're not going to try to repair it yourself, you should reassemble it and have it repaired.
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Old 15th August 2010, 09:21 PM   #9
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I understand. I'll pull it back apart and get those FETs yanked. I really do appreciate all the help and admire those of you that have elevated electronic repair to an art form.
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Old 15th August 2010, 09:51 PM   #10
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I should have known better.....

Anywho, here's the numbers:

Q05:
1-2 = 11.1
1-3 = 245.3
2-3 = 234.6

Q11:
1-2 = 31.56k
1-3 = 31.58k
2-3 = 235.6

I also check all the gate resistors again and found R16 now reads 111.3. All the others were still around 100.1 to 100.2. Yes, I had checked them earlier with the FETs removed. But, I guess I'll need to at least replace R16. I guess they are 1206 size, but what other specs do I need to know to order from digikey. (wattage, pulse withstanding, etc.)
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