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Old 3rd November 2005, 04:18 AM   #1
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Question amp protection circuit malfuntion

I have a newer Lanzar opti 1000d and recently it turned on with the protection circuit activated with a red light instead of a green light. I pulled the amplifier apart to find that a screw had gotten loose somehow and touched the circuit board, it touched one of chips simalar to appearence to this one (http://n1vg.net/opentracker/images/chip-large.jpg) I know this due to the mark on one of the pins. can anyone help me troubleshoot this problem and give me and idea what could have blown or what to check. any help is appreciated!
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Old 3rd November 2005, 05:56 PM   #2
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Hi androtaker56

Can you maybe post a couple of photo's of the IC that was shorted by the screw? As well as the IC number? It would be a bit easier, as I do not know what IC was shorted (Could be an OPAMP, Comparator, PWM IC, ClassD control IC, etc). For now I'd recommend looking for any obvious problems, like burnt resistors, diodes, all the usual stuff. Also do you maybe have a schematic, then I'll be able to be more specific to help solve the prob.

Regards,
Werner
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Old 3rd November 2005, 06:02 PM   #3
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Thats your PWM IC. You could always desolder it and replace it if you have decent soldering skills.
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Old 3rd November 2005, 06:31 PM   #4
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It may also be one of the other IC's that I have mentioned. I have seen alot of car amps whose protection circuit relies on more than just the PWM IC.
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Old 4th November 2005, 06:50 AM   #5
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I have been searching for schmatics on it but no luck yet. as for the photos I will try to post them as soon as possible. but I should be able to get it on here tomorrow if I remember. ill also post the chip number.
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Old 5th November 2005, 07:26 AM   #6
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heres a pic of the chip attatched, this is the actual amp.
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File Type: jpg closeup.jpg (26.2 KB, 307 views)
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Old 5th November 2005, 11:07 AM   #7
sdoom is offline sdoom  Germany
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that looks like a dual-flipflop IC. here is the Datasheet

http://www.fairchildsemi.com/ds/CD/CD4013BC.pdf


Itīs probably used for the protection curcuit, but it could also be used for a square wave generator to drive the mosfets. Is there no IC with the numbers 494 , 2525 or 3525 on the board ?

As you say the amp always stays in protection mode, itīs more like that the power supply (including the protection curcuits) are ok and itīs more likely that the music-power section has a fault. Check for shorts in the music section power parts.
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Old 5th November 2005, 06:44 PM   #8
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yeah theres a tl494cn. its on the opposite side of the amp that the one marked is
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Old 5th November 2005, 06:44 PM   #9
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heres a pic of the whole amp
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File Type: jpg whole amp_033.jpg (27.5 KB, 290 views)
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Old 6th November 2005, 08:55 AM   #10
sdoom is offline sdoom  Germany
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Hi


ok, I`m not too familiar with digi-amps, but the protection curcuits basically follow the same rules as they do in analog amplifiers. "If anything goes wrong ---> disable the PWM-controller".

The PWM-controller is the TL494 , that means this IC delivers the driving signal for the SMPS-mosfets and controls everything that has to do with the SMPS.

But the protection is usually done with a couple of transistors or a Op-Amp IC. (that could be the small IC next to the 494 on your picture) , in korean amplifiers this usually is a KIA4558 - OpAmp.
Usually the protection curcuit is divided , that means there are more than one protection curcuit. E.g. one monitors the temperature, the other one is activated by a short @ the output stage of the music amplifier.

The protection curcuits usually combine their output signal , this is fed to the TL494. The TL494 has an output control pin, but in most car amplifiers this pin is always connected to the reference voltage pin (The TL494 has a precision volatge output pin that delivers 5V) , that means the TL494-outputs are always enabled. The shutdown function usually is achieved with the error-amplifiers of the TL494 .

Here you find a basic application of the TL494 . in most amplifiers the TL494 is used in the same way or close to that. There you see whenever one op-amp delivers 5V at itīs output, the TL494 is shut down and the red LED is turned on.


TL494 application ( car amp)


Try to find similarities with your amplifier. You should be able to find out where the shut-down signal comes from in your amplifier.

BTW: When you want to power up your amp on the workbench add a 2Ohm/10W resistor in series to the +12V power cable. this will prevent parts when there would something go terribly wrong , or use a power supply that will only deliver 1-2Amps
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