alpine 3553 amp, 5 amps at idle & runs hot - diyAudio
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Old 17th June 2010, 09:17 AM   #1
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Default alpine 3553 amp, 5 amps at idle & runs hot

my alpine 3553 amp got flooded a while ago, all the 2sd1669 ( 6pcs ) blew so i replaced them, now the amp works but runs extremely hot and draws 5 amps, even without speakers attached. any suggestions on what to do? a tech guy here said i should adjust the bias, any one care to explain how this is done?
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Old 17th June 2010, 09:32 AM   #2
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With all transistors clamped tightly to the heatsink, does the heatsink heat up under the power supply transistors (the ones you replaced) or under the output transistors?

If it gets hot under the outputs, the bias may need to be adjusted, especially if someone has moved them from their original setting.

It's also possible that some component has been damaged by the moisture and that's causing the overheating.
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Old 17th June 2010, 11:11 AM   #3
Plammox is offline Plammox  Denmark
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If it turns out not to be the bias:
Were the old transistors isolated from the heatsink, or was the heatsink isolated from the chassis previously?
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Old 18th June 2010, 03:19 PM   #4
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its heating up under the power transistors i replaced, it only takes a couple of minutes to get really hot. turns out there are no provisions to adjust the bias, i dont see any trim pots. the transistors are clamped to the heat sink, any suggestions what to check out next?
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Old 18th June 2010, 03:21 PM   #5
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I don't have any information on that amp. Can you post a photo of the inside of the amp (specifically the area near the transistors you replaced).
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Old 19th June 2010, 06:51 AM   #6
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here some pics
Click the image to open in full size.

Click the image to open in full size.
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Old 19th June 2010, 09:25 AM   #7
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There are 1 and 10 ohm resistors just in front of the power supply transistors you replaced. You need to check each of them to confirm that they're within tolerance.

If those are OK, check the C3852 transistors. You will need to desolder them to check them.
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Old 24th June 2010, 09:52 AM   #8
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i checked the resistors and they read all 1.5 and 4.5, i attribute the 4.5 ohm reading to the fact that its connected to the transistor. i replaced the c3852 transistors, turns out they weren't bad. Now the power supply goes up to 10 amps when i turn the amp on! what did i do wrong?
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Old 24th June 2010, 10:02 AM   #9
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Remove the resistor and re-check it.
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Old 28th June 2010, 02:20 AM   #10
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rechecked the resistors, they're .5 ohms over spec, is that a big deal? or is that within acceptable spec?
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