Hi all.
I was wondering if anyone could point me in the right direction.
Playing a 1khz test tone into the amplifier, Left channel is pretty good. Right channel is damaged.
I was wondering what the most likely faulty component is. I was going to order a pair of transistors. But thought it would be a good idea to ask on here first.
Left reading 15 volts and right reading 8 volts. (Under no load)
Thanks.
I was wondering if anyone could point me in the right direction.
Playing a 1khz test tone into the amplifier, Left channel is pretty good. Right channel is damaged.
I was wondering what the most likely faulty component is. I was going to order a pair of transistors. But thought it would be a good idea to ask on here first.
Left reading 15 volts and right reading 8 volts. (Under no load)
Thanks.
No schematics... okay, measure all Vbe, Vce and see if the readings look normal. Vbe = around 0.6V, and Vce not equal to 0V (which may signify a shorted transistor).
Visual test ... anything look burnt?
Smell test ... anything smell burnt?
Touch test ... anything too hot to touch?
You're in luck, you have a working channel. Just compare voltage readings with the other channel for reference. Maybe you can narrow down which stage/section is the culprit.
Visual test ... anything look burnt?
Smell test ... anything smell burnt?
Touch test ... anything too hot to touch?
You're in luck, you have a working channel. Just compare voltage readings with the other channel for reference. Maybe you can narrow down which stage/section is the culprit.
Nothing is getting hot. (quick measurements with ir thermometer)
No popped / bulged caps.
Should I get a data sheet on the transistors and test the pi s directly?
No popped / bulged caps.
Should I get a data sheet on the transistors and test the pi s directly?
The scale on both channels is not the same.
Do you know how to use a scope?
No doubt, you don't even give us brand and model.
We also need a few sharp pictures of the front, back, and inside.
Specially the transistors, transformer and power supply.
Do you know how to use a scope?
No doubt, you don't even give us brand and model.
We also need a few sharp pictures of the front, back, and inside.
Specially the transistors, transformer and power supply.
One possible cause: problem in the power supply of that channel - if it is too low, the output also is.
You really need a schematic. And a multimeter.
Jan
You really need a schematic. And a multimeter.
Jan
The scale is the same on the pictures. The images went funny when I resized them.
I know the basics with a scope.
It's a vibe black box 4 from 2003
I'll take some pictures after work. But it's mat black solder mask. Really hard to trace.
I know the basics with a scope.
It's a vibe black box 4 from 2003
I'll take some pictures after work. But it's mat black solder mask. Really hard to trace.
I probed the pins on the 6 large transistors. The sine. wave is almost square like the output.
I'm going to take the board out next and test the voltage of those four big caps. That I'm guessing are the output caps from a switch mode power supply for each channel.
Last edited:
1) you forgot to tell us a most important detail: it's a CAR amp !!!!
Very different from what we normally see here.
I didn't find the transformer until I noticed the ferrite toroid surrounded by quite small supply type caps,into what looks like the PSU area.
I suggest you ask the Moderator to move this to the Car Audio area, where they have more experience on this and in fact might know this amp very well.
Not obscure at all ... in the Car Audio World.
Side note:
shows two waves side by side, as if inviting comparison .... which can't be compared at all.
The left one shows 4 vertical (voltage) divisions (meaning 4 horizontal lines) , the right one shows 8 . 😱
That's not a "resizing" problem but using different voltage scales ... unknown to us by the way.
The left one shows 13 horizontal (time) divisions, worse is that they are irregular 😱 , never seen anything like that on a scope screen; the space between 4 and 5 is wider and between 8 and 9 is narrower.
Yet the sinewave looks regular (it should be horizontally distorted at those points). Weird.
The right one shows 24 horizontal (time) divisions .
Unknown voltage scales, unknown time scales, for all we know the left signal might be a 1 KHz sinewave and the right one the SMPS 40 KHz switching signal ... or anything else.
EDIT: you speak of left and right, but this is a 4 channel amp.
So what does that mean?
You use 2 of them for left and righ?
Are they bridged?
Please move this to Car Audio section.
Never seen anything like that.
Very different from what we normally see here.
I didn't find the transformer until I noticed the ferrite toroid surrounded by quite small supply type caps,into what looks like the PSU area.
I suggest you ask the Moderator to move this to the Car Audio area, where they have more experience on this and in fact might know this amp very well.
Not obscure at all ... in the Car Audio World.
Side note:
shows two waves side by side, as if inviting comparison .... which can't be compared at all.
The left one shows 4 vertical (voltage) divisions (meaning 4 horizontal lines) , the right one shows 8 . 😱
That's not a "resizing" problem but using different voltage scales ... unknown to us by the way.
The left one shows 13 horizontal (time) divisions, worse is that they are irregular 😱 , never seen anything like that on a scope screen; the space between 4 and 5 is wider and between 8 and 9 is narrower.
Yet the sinewave looks regular (it should be horizontally distorted at those points). Weird.
The right one shows 24 horizontal (time) divisions .
Unknown voltage scales, unknown time scales, for all we know the left signal might be a 1 KHz sinewave and the right one the SMPS 40 KHz switching signal ... or anything else.
EDIT: you speak of left and right, but this is a 4 channel amp.
So what does that mean?
You use 2 of them for left and righ?
Are they bridged?
Please move this to Car Audio section.
Never seen anything like that.
Last edited:
Haha sorry. I thought the amps would be pretty much the same after the power supply. (which seems to be working fine)
The front two channels are working fine. It's the rear channels I'm working with.
I'll re upload the scope pictures. And try and get the thread moved.
The front two channels are working fine. It's the rear channels I'm working with.
I'll re upload the scope pictures. And try and get the thread moved.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Both with the same 1khz test tone.
If you decrease the 1kHz input amplitude do you get sine waves out of the bad channel? Or is it just smaller square waves?
The distorted channel looks heavily clipped. Look for a ground trace blown open or a shorted input transistor. Follow the signal through the amp and see where it starts to clip. I think you are getting way too much gain somewhere.
Okay so I noticed one pnp transistor on the front which I thought was fine was red hot. Removed it and it reads as a pair of diodes on a cheap ebay component tester.
On the bad channel, I removed the four big transistors and then probed the empty holes to fine clean signal.
So I'm wondering if they're dodgy transistors or is it because I've opened a circuit?
On the bad channel, I removed the four big transistors and then probed the empty holes to fine clean signal.
So I'm wondering if they're dodgy transistors or is it because I've opened a circuit?
Follow the circuit after the overheating transistor. There's likely something shorted downstream causing it to overheat.
You might want to repost this in the car audio section. Perry Babbin is always watching that part of the forum and is excellent at troubleshooting these things.
Seeing the screens I believe the fault is closer to the input than the output, compare both channels before clipping and you'll see the slope on both signals is the same, and after you told that the clipped signal is the same at low volume it means that the output is fine and is amplifying the problem that is before the output stage, if it were an output fault or a power fault the clippin will occur always at the same output voltage, it wont decrease with the signal.
On the other hand, on cars amps the dominant technology these days is Class D, so it would help you to read in that section too.
Regards!
- Status
- Not open for further replies.