So I'm about to take a stab at repairing an alpine head unit for a car with non working preouts. There are a number of small smd components and some are unmarked. I'm assuming there's a resistor, or capacitor as small as 0401 causing this, hopefully just an IC, but how would I calculate the value of the part if it's blown or bad?
I don't blame you for wanting to repair something that probably has a simple fix. In this case however, you can't get very far without a schematic for the circuit.
I will add that since it is bad for both channels, a chip or power supply is a start. Something common to both channels.
I will add that since it is bad for both channels, a chip or power supply is a start. Something common to both channels.
I've been trying to get hold of Alpine support in 5 different countries so far with not a single word of a reply. Even just general inquiries.
Yes, all three preout channels are dead, front, rear, sub... everything else is perfect. I'll try to test the volume chip, but if that's dead I'd like to check if it's power to the chip, or the chip itself. I'm just trying to prepare as much as possible really in the event it is something like a component to ground shorted or something.
Yes, all three preout channels are dead, front, rear, sub... everything else is perfect. I'll try to test the volume chip, but if that's dead I'd like to check if it's power to the chip, or the chip itself. I'm just trying to prepare as much as possible really in the event it is something like a component to ground shorted or something.
I'd say, you will never ever get a schematic for that.
However, there is something you could do.
State the model number, show a high resolution and sharp picture of the area you suspect, find sample applications for the ICs and structurally compare to present parts on your PCB. Also, try to beep out components.
However, there is something you could do.
State the model number, show a high resolution and sharp picture of the area you suspect, find sample applications for the ICs and structurally compare to present parts on your PCB. Also, try to beep out components.
The model is X701D-A4.
There are traces coming out of a custom dsp chip which is working, they go to a volume IC and then split to opamps. I suspect the issue is the volume ic, power running to it, or something like that as everything is working aside from preout section.
I just ordered a new microscope so that will be helpful at least, and I still have yet to trace the lines on the reverse side of the board.
I'm just going to go through the other IC's to make sure there is another volume chip as the volume for the main amplifier is properly working, I'm just doing a stupid thing and assuming that chip only controls preout volume after signal processing.
There are traces coming out of a custom dsp chip which is working, they go to a volume IC and then split to opamps. I suspect the issue is the volume ic, power running to it, or something like that as everything is working aside from preout section.
I just ordered a new microscope so that will be helpful at least, and I still have yet to trace the lines on the reverse side of the board.
I'm just going to go through the other IC's to make sure there is another volume chip as the volume for the main amplifier is properly working, I'm just doing a stupid thing and assuming that chip only controls preout volume after signal processing.
Attachments
If you have an oscilloscope, use it or a signal tracer to follow the audio from the DAC or processor through op-amps and up to the RCA jacks.
If you have no signal at the op-amp output, it may be a mute circuit issue or the op-amp itself is dead.
I agree, likely related to the volume control as all 3 channels affected. Here is the 1st page of the datasheet to grab pin numbers to probe around on it. The part is "not for new designs" according to I think it was digikey. Possible problems are as you say, power, fried or possibly whatever sends the I2C commands to it has a problem.
Any chance the preouts are just turned off in the settings?
I see in the manual the rear and subwoofer preouts can be turned on/off.
I see in the manual the rear and subwoofer preouts can be turned on/off.
Yea, I'll get it apart again this weekend, hopefully it will be a labeled part that's dead! First thing I'll do is check the power there and peek at the thermal camera. Then trace signal and see.
I'd suggest you ask a moderator to move your post to the car audio section.
where people that repair car audio all day tend to reside....
where people that repair car audio all day tend to reside....
And this is where threads go to die! 🤣
So let's go hypothetical...
Let's say a resistor or capacitor to ground is shorted and unmarked..
Would there be a safe, trial and error way of testing a new component? I'm assuming since it's already shorted and not doing any further harm, starting with a higher impedance or an average capacitance, depending on application, wouldn't do much harm. Though I would think that it could be calculated judging by the surrounding components in the circuit somehow no?
So let's go hypothetical...
Let's say a resistor or capacitor to ground is shorted and unmarked..
Would there be a safe, trial and error way of testing a new component? I'm assuming since it's already shorted and not doing any further harm, starting with a higher impedance or an average capacitance, depending on application, wouldn't do much harm. Though I would think that it could be calculated judging by the surrounding components in the circuit somehow no?
Yes, and one method is to get the data sheets for the chips in the area of, or that have traces going to the dead unknown component. Then you have an idea of the application / circuit and this may help narrow down a value. If you’re really lucky the chip data sheet will have a few examples of applications with schematics and values similar to yours.
Another way is to look for repetition of circuitry, like left and right channels in audio. If the dead component is one channel, chances are the same component in the other channel is still good, and you can measure the value. Again, the chip data sheets are a big help with this.
Another way is to look for repetition of circuitry, like left and right channels in audio. If the dead component is one channel, chances are the same component in the other channel is still good, and you can measure the value. Again, the chip data sheets are a big help with this.