I picked up this amp for 30 bucks knowing it wasn't working properly. I powered it from my car battery and it powered up fine so I connected a subwoofer and audio in and no sound. I opened up the amp and noticed a burnt trace on the bottom side of the board. I repaired the trace and tried it again. I'm getting mild bass out of it but also a scratchy distorted sound. I'm lost at this point,any suggestions?
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What circuit was the burned trace in?
Have you tried operating all pots and switches through their entire range to see if that made a difference?
Do you have a scope?
Have you tried operating all pots and switches through their entire range to see if that made a difference?
Do you have a scope?
I'm not sure what circuit it was in, it was between the blue 106k250v caps, one of the pins on the driver board and to a resistor that is connected to tl074cn
I tried all the pots and switches through their entire ranges and gave them a wiggle and didnt seem to have any effect on it.
Unfortunately no scope.
I tried all the pots and switches through their entire ranges and gave them a wiggle and didnt seem to have any effect on it.
Unfortunately no scope.
Do you have positive and negative rail voltage?
Do you have positive and negative regulated voltage on the power supply pins of the op-amps?
Do you have positive and negative regulated voltage on the power supply pins of the op-amps?
Hi Perry, I have rail voltage(35v) and I'm getting 27v between Vcc+/- pins on the op-amps. Since my last post I discovered a shorted transistor on the driver board I believe it is a 2SA1797-Q. I've removed it from the board to test it just to make sure it was the trasistor that was shorted. Is it common for these devices to go bad or should I be looking for other bad components that may have caused it to short out?
Photo of location of shorted transistor?
Did you replace it with an exact replacement?
What were the markings on it?
Was the rail voltage ±35v?
Did you replace it with an exact replacement?
What were the markings on it?
Was the rail voltage ±35v?
Is that a photo of the driver board in your amp? Or a photo from some other amp?
The transistor you pointed to is in the protection circuit. If it's shorted, it could cause the signal to be badly distorted.
The transistor you pointed to is in the protection circuit. If it's shorted, it could cause the signal to be badly distorted.
The signal is badly distorted. When I was testing the voltages I turned up the gain with audio and the amp went into protection mode
Hi Perry, so I replaced the transistor(2sa1797) and the distorted sound issue has gone which is great but the output from the amp is very low,even with the gain set to max. It may be possible that my head unit connection are to blame. Since the head unit doesn't have subwoofer out, I paralleled the rca's for the rear output on the head unit and used one set of rca's for sub output but that setup worked fine with my kenwood mono amp rated at quarter of the power this amp is rated
So I swapped out my head unit with one that has rca's for a sub output and the amp is actually working great. Hopefully it stays that way. Thanks for your input and the advice on checking the resistors, there was one 4.7ohm that was open that I had to replace also
That 4,7 ohm was in series with the protection circuit transistor that failed.
The 470 ohm resistors often open when the protection circuit is engaged for an extended period of time.
The 470 ohm resistors often open when the protection circuit is engaged for an extended period of time.