So the 1k resistor was installed to give the circuit feedback. Is there a section in tutorial that explains the feedback circuit a little further.? Would it be easier to troubleshoot a broken connection in the feedback loop with or without the 1k.
There are many sections on feedback. You have to read all sections and follow all links (reading the linked pages top to bottom). There's no way to cover every aspect of every possible circuit in any tutorial. You have to read (until it's clear) all sections and see how they apply to the amp you're repairing.
In this amp, the BD_OUT is the feedback. It gets back to the servo/feedback op-amp via R316.
In this amp, the BD_OUT is the feedback. It gets back to the servo/feedback op-amp via R316.
Perry I have continuity from r316 to the speaker termunal. I also have continuity from pin 2 of r300 to the opposite side of R316. I also removed R313 and R317 to isolate that output.
Pin
1= 4.5v
2= 0.003v
3= -0.058v
Why do I still have 4.5 on pin 1 am I missing something?
Pin
1= 4.5v
2= 0.003v
3= -0.058v
Why do I still have 4.5 on pin 1 am I missing something?
With R317 removed pin 7 has a nice square on the output. To me it looks like u301 is defective unless I am missing something
I replaced u301 and still have 4.5v. I lifted pins 1,2,3 for curiosity and probe to grd I have 4.5 on all 3 legs.
I installed all the resistors back the way it should. Negative probe on grd and pin voltages on u300.
Pin
1= -4.5v
2= 0.110v
3= 0.004v
4= -6v
5=-0.025
6= -4.35
7= 5.79v
8= 6v
Pin
1= -4.5v
2= 0.110v
3= 0.004v
4= -6v
5=-0.025
6= -4.35
7= 5.79v
8= 6v
For both sets of voltages that you posted, the voltage on pin 1 was correct. That meant that the op-amp was working as it should. For the second set of voltages, 168mv on the output shouldn't produce 110mv on the inverting input.
What's the DC voltage on pin 7 of U300?
What's the DC voltage on pin 7 of U300?
U301. U300. Spkr terminal = 0.107v
Pin
1= -4.36v. 0.001v
2= 0.014v. 0.003v
3= 0.003v. 0.005v
4= -5.99v. -6.00v
5= -0.025v. -0.002v
6= -4.36v. 0.002v
7= 5.83v. 0.002v
8= 6.07v. 6.06v
Pin
1= -4.36v. 0.001v
2= 0.014v. 0.003v
3= 0.003v. 0.005v
4= -5.99v. -6.00v
5= -0.025v. -0.002v
6= -4.36v. 0.002v
7= 5.83v. 0.002v
8= 6.07v. 6.06v
Those op-amps appear to be working as they should.
Post the voltage on U302.
In the future, post the ICs in a vertical line. If you're trying to avoid re-typing the pin numbers, copy and paste.
Post the voltage on U302.
In the future, post the ICs in a vertical line. If you're trying to avoid re-typing the pin numbers, copy and paste.
I am slightly confused why the 4.5v on the output if the input are close to zero?
U301
1= 4.27
2= -0.004
3= 0. 001
4= -6.00
5= -0.022
6= 4.39
7= -4.29
8= 6.06
U301
1= 4.27
2= -0.004
3= 0. 001
4= -6.00
5= -0.022
6= 4.39
7= -4.29
8= 6.06
Sorry I was just frustrated and trying to figure where I was going wrong trying to determine how the op amp functioned. I was under the impression that 0 on both inputs would yield a 0 on tje output.
Read the page on op-amps (online if you don't have the tutorial).
You can have any voltage (as far as the op-amp can swing) with 0.000v on both inputs. the op-amp drives (in a circuit with local feedback) the output to make the inverting input match the non-inverting input. There is a bit of error so they may not match exactly but they will be close.
This amp is like a huge op-amp. The feedback and the drive signal drive pin 2 of U301. All of the components after pin 1 of U301 are essentially in the feedback loop.
You can have any voltage (as far as the op-amp can swing) with 0.000v on both inputs. the op-amp drives (in a circuit with local feedback) the output to make the inverting input match the non-inverting input. There is a bit of error so they may not match exactly but they will be close.
This amp is like a huge op-amp. The feedback and the drive signal drive pin 2 of U301. All of the components after pin 1 of U301 are essentially in the feedback loop.
Perry,
This morning I tried a different approach. I kept the hv disconnected and applied a 60hz signal into the rca input and traced input to pin 2 of the u301. At this point I believe my feedback loop is not broken and for some reason I cannot get both drive signals to from both opamps to operate simultaneously without some sort of input signal. Pin 1 had a small sine wave from audio and the output had a nice square wave on pin 7 of U301 and u302.
This morning I tried a different approach. I kept the hv disconnected and applied a 60hz signal into the rca input and traced input to pin 2 of the u301. At this point I believe my feedback loop is not broken and for some reason I cannot get both drive signals to from both opamps to operate simultaneously without some sort of input signal. Pin 1 had a small sine wave from audio and the output had a nice square wave on pin 7 of U301 and u302.
Did you reinstall the 1k resistor?
Without the outputs functioning, there is no output from them to send feedback back to the op-amp. That's why you have to use the resistor to provide local feedback.
Without the outputs functioning, there is no output from them to send feedback back to the op-amp. That's why you have to use the resistor to provide local feedback.
Correction to the statement above after applying and audio signal to the input the drive circuitry is operating as it should. I removed the input signal and now there are 2 drive signals on both u301 and u302. Perry any thoughts on this. The amp operates as it should.
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