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IT's good that you have the right hand side working now. Have you tested with any audio or a signal generator?
It would be worth removing the fuse from the + supply and inserting your DMM across the fuse receptacle and switched to a current range, probably 200mA, and then switch on and see what current is flowing in the O/P stage. I would expect it to be in the range of 10 to 50mA. Do this with no load on the output and with ideally the the power Amp input shorted. If not turn the volume control down to minimum and the measure. Make a note of the value.
It would be worth removing the fuse from the + supply and inserting your DMM across the fuse receptacle and switched to a current range, probably 200mA, and then switch on and see what current is flowing in the O/P stage. I would expect it to be in the range of 10 to 50mA. Do this with no load on the output and with ideally the the power Amp input shorted. If not turn the volume control down to minimum and the measure. Make a note of the value.
OK. That more or less answers my question. I was interested in how much quiescent current is flowing in the output of the working amp'. I suggest you now use the working amp as a template for the non working one. Take strategic voltage readings form the working one to diagnose and fix the non functioning one.
Yeah that was my thought's to
I think you need to go back a step and measure the quiescent current as I suggested earlier. Also, measure the d.c voltage on the output with no signal present and the input shorted. This should be low, certainly less than 100mV.
You really must get one bit at a time working correctly otherwise you just end up chasing your tail all the time.
You really must get one bit at a time working correctly otherwise you just end up chasing your tail all the time.
Thanks for the advice,
When you say input shorted, do you litteraly mean short + to -- where the input signal comes in,
Also when you say output, where exactly do you mean?
I can take as many readings and change as many parts as required but you need to be clear with your instructions,
As i said before, i am still learning, i know 12VDC single phase and three phase AC electric realy well, i do it for a job now,
Its the 0V part i have difficulty in understanding but i am getting better,
So, what would you like me to test ?
Thank you for your time and help, it realy is appreciated,
Pete
No i dont sorry, although i was thinking of buying an oscilloscope
bertus
Moderator
Hello,
When you do only audio work, you can have a signal generator and scope for about 100 pounds:
https://www.amazon.co.uk/Topiky-Function-Generator-Portable-FG-100-default/dp/B083TGVZ3Y
https://www.amazon.co.uk/Digital-Oscilloscope-ETEPON-Source-15001K/dp/B07FPDY3DK
Bertus
When you do only audio work, you can have a signal generator and scope for about 100 pounds:
https://www.amazon.co.uk/Topiky-Function-Generator-Portable-FG-100-default/dp/B083TGVZ3Y
https://www.amazon.co.uk/Digital-Oscilloscope-ETEPON-Source-15001K/dp/B07FPDY3DK
Bertus
Thats great thanks, i think thats mainly where my interest lies with audio equipment, will those 2 pieces of kit be usefull?, if so i will buy them, thanks
bertus
Moderator
Hello,
I was originaly looking for the nano scope, but that has a much higher price:
https://www.amazon.co.uk/Seeedstudio-109990013-DSO-Nano-v3/dp/B078YJYJDR
Bertus
I was originaly looking for the nano scope, but that has a much higher price:
https://www.amazon.co.uk/Seeedstudio-109990013-DSO-Nano-v3/dp/B078YJYJDR
Bertus
Those two items will be of more use than you could possibly imagine. They will make your fault finding so much easier. You will have to take a little time to get accustomed to them, especially the scope where you will have interpret what you are seeing and how to set it up. It won't take too long though and will be worth all the effort you put into it.
Ok. I will try to be more explicit with my instructions.
To check the output voltage, short the junction of R69 and C42 for the R.H. channel or R12 and C34 for the left hand channel to the nearest 0V connection on the PCB.
You will sometimes see 0V referred to as Ground. These are not to confused with Mains Earth.
Next make sure there is no load, test resistor or speaker, on the output of the channel you are testing.
Connect + lead of your DMM to the O/P of the Channel under test and the - lead to 0V at the power supply.
Set your DMM to 2V d.c. or whatever range you have in that region.
Turn on your amplifier and check the voltage reading on your DMM.
It should be less than ± 100mV or preferably less than ± 50mV. If you get substantially more then you have a problem.
You will next need to check the quiescent current but we will deal with that on another post.
You will sometimes see 0V referred to as Ground. These are not to confused with Mains Earth.
Next make sure there is no load, test resistor or speaker, on the output of the channel you are testing.
Connect + lead of your DMM to the O/P of the Channel under test and the - lead to 0V at the power supply.
Set your DMM to 2V d.c. or whatever range you have in that region.
Turn on your amplifier and check the voltage reading on your DMM.
It should be less than ± 100mV or preferably less than ± 50mV. If you get substantially more then you have a problem.
You will next need to check the quiescent current but we will deal with that on another post.
Is this a better option?
Are these points still valid ?
I will try to xo this tomorrow and post my results
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