Electronics > Beginners

Anyone with a Vibe CBR12 car powered subwoofer.

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qoole:
Hiya,

I have recently been asked to repair a Vibe CBR 12 powered sub. Having traced the board out and found the problematic area (the SMPS PWM IC) I noticed something else.

If anyone has one of these and is willing to pop the back cover off and take a photo of the main board for me I'd much appreciate it.

On the board in front of me I have a slot marked 'R81' with a resistor silkscreen footprint but the actual component is a Ceramic 100nF cap.
What I want to know is it a wrong component or a silkscreen mistake?

Thanks,

Alex

EDIT: I have attached a photo of the cap in question. Please also notice the audio wankery (to use one of Dave's phrase) of 'Vibe' branded Electrolytics!

Jonny:
Would be curious to know but probably irrelevant. Trace the circuit and look at datasheet for IC  http://www.fairchildsemi.com/ds/KA/KA3525A.pdf  and decide if it should be a cap or resistor. Either way, it used to work so is probably ok (i.e. slikscreen error)

I've seen a few failed car amps and is usually FETs and associated drive transistors and resistors that get smoked along with them, doesn't usually take out the drive IC but I guess anything's possible if it went bang loud enough.

SeanB:
Probably was a resistor to trim voltage a little in production, but was replaced by a capacitor ( who cares if the voltage it makes now is 5% different) as it had an oscillation problem and this was an easy way to reduce loop gain and calm it. Most likely you have a lot of crispy FETs and drivers, along with some burnt resistors, along with the failing "Vibe" OHL junk caps that caused the carnage by going high ESR. Replace them all, and the caps as well, and put a 6A diode across the input as a crowbar diode as well, it might have been reverse connected. Power up with a H1 lamp in series with the power ( or a 20A power supply) with both filaments in parallel, so that you do not fry anything too fast if there is another fault.

Edit: Check that optoisolator D9 as well, I do not trust them at all. It looks like C14 has popped the bottom seal in any case, from the stain on the PCB.

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