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Stage Line 500W amp repair project

I was going to suggest that you connect your signal generator to you scope and have a play with them trying out different setting to see what happens. This will get you accustomed to using them and to have some idea of what to expect with various setups. A BNC to BNC lead would be the easiest way to connect the two together but you could also do so using one of the BNC to Cro Clip leads and one of your Scope leads.
 
I was going to suggest that you connect your signal generator to you scope and have a play with them trying out different setting to see what happens. This will get you accustomed to using them and to have some idea of what to expect with various setups. A BNC to BNC lead would be the easiest way to connect the two together but you could also do so using one of the BNC to Cro Clip leads and one of your Scope leads.
Yes i have already done this as i have 2 sers of BNC to crock clip leads
 
If you do decide to buy a BNC to BNC, get a 50Ω lead as well as a direct connection.
It had me scratching my head only getting half the peak to peak voltage.

Martin
 
I am at the point where the protection circuit is no longer activating and the unit powers up with no faults, the left chanel has little to no output at all, the right chanel has some amplification but is badly distorted, the pre amp and gain seems to work ok on both chanels
 
Read these instruction through before acting upon them!

Take a note of all the input and output conditions for the following tests.

These tests are conducted with no output load unless otherwise stated.

1) Connect your Sig' Gen' to one of the inputs of your amp. You may have to make a suitable lead unless you can access the input connector from inside your amp'.

2) Using one of your Scope' leads Connect the input of your Scope' to the appropriate output of your amp.

3) Set the Sig' Gen' output to 1KHz sine wave to a level of 100mV.

4) Set the output of your Scope to 10V/div'.

5) Turn the amp's volume control to minimum.

6) Turn on the Amp'

7) Monitor the Scope to see if there is any output that should not be there.

8) Whilst still monitoring your Scope', gradually turn up the Amp's volume control. Check that the output is still a clean sine wave.
You may need to adjust the volts per division of you Scope' to get a full screen display.

9) The output of your amp should be a faithful reproduction of the input signal and should be symmetrical about 0V i.e. of equal magnitude above and below 0V.

10) If the output is not as it should be, take a clear picture of your scope screen and post on here.

11) If the output is clean, gradually turn up the amp's volume control until you get max output from the amp'. Max output is just as the tops and bottoms of the sine waves start to flatten off. This is known as Clipping and in normal use is a condition to be avoided.

12) Back off the volume control until you amp' is just out of clipping.

13) Make a note of the peak to peak voltage.

14) Repeat for the second channel

15) Report all of your results here.
 
Read these instruction through before acting upon them!

Take a note of all the input and output conditions for the following tests.

These tests are conducted with no output load unless otherwise stated.

1) Connect your Sig' Gen' to one of the inputs of your amp. You may have to make a suitable lead unless you can access the input connector from inside your amp'.

2) Using one of your Scope' leads Connect the input of your Scope' to the appropriate output of your amp.

3) Set the Sig' Gen' output to 1KHz sine wave to a level of 100mV.

4) Set the output of your Scope to 10V/div'.

5) Turn the amp's volume control to minimum.

6) Turn on the Amp'

7) Monitor the Scope to see if there is any output that should not be there.

8) Whilst still monitoring your Scope', gradually turn up the Amp's volume control. Check that the output is still a clean sine wave.
You may need to adjust the volts per division of you Scope' to get a full screen display.

9) The output of your amp should be a faithful reproduction of the input signal and should be symmetrical about 0V i.e. of equal magnitude above and below 0V.

10) If the output is not as it should be, take a clear picture of your scope screen and post on here.

11) If the output is clean, gradually turn up the amp's volume control until you get max output from the amp'. Max output is just as the tops and bottoms of the sine waves start to flatten off. This is known as Clipping and in normal use is a condition to be avoided.

12) Back off the volume control until you amp' is just out of clipping.

13) Make a note of the peak to peak voltage.

14) Repeat for the second channel

15) Report all of your results here.
I will try do this ASAP
 
Ok, i connected my sig gen to the rleft chanel as this is the worst one, injected 1000hz sine wave, connected my scope to the output, no gain/volume the scope reads nothing, turn the volume up and i get 1.000hz, see photos, same for the right chanel,
Not sure on the peak to peak voltave20210219_183251.jpg 20210219_183307.jpg 20210219_183313.jpg 20210219_183321.jpg 20210219_183329.jpg
 
CIMG4399.JPG CIMG4399.JPG CIMG4398.JPG CIMG4397.JPG CIMG4396.JPG

The output signal looks as though it might be a bit distorted.

Is your scope single or dual channel?

If it is dual channel, can you connect it to the output of your sig' gen' so that it is displayed on the same screen so that we can do a comparison.

If not, can you take a separate picture of the sig' gen' output.

Did you manage to get your amp's output up to the point of clipping. Your scope is showing 20V peak to peak (Pk to Pk) output. I would have expected it to be at least 80V Pk to Pk. You can always increase the sig' gen' output to achieve it.

A further question, are you getting the same output level on each channel for the same input level?

Also, for maximum resolution, can you expand the signal on your scope so that it occupies the full depth of the screen.

What is the green LED indicating in the last picture?

Plus some pictures of my work room and a recent project!
 
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My scope is single chanel, i didnt manage to get it to clip and i did increase the sig gen output but something started to fizzle, i think it was a resister fuse, as for the same output level i will have to check, the green led is just stereo indicator the one next to it is bridged,
And thats an impressive work room :)
 
Can you track down which fusible resistor it was. Did it fail or just get hot?

All that junk in my work room has taken many years to accumulate.
 
If it was the fuse resiator it was F2, its burned but not gone open circuit, thats +45v for the right chanel, it was when i cranked the sig gen output up
 
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