Measuring Vpp Sony PS-X9 with Rigol DS1054Z

I am having some difficulties measuring Vpp with my Rigol DS1054Z. According to the Sony service manual I have to adjust two pots so that it measures 6Vpp for H1 and H2 (after removing a bridge and feeding the circuit 1VDC).

Somehow I can't get a stable sine wave and the Vpp fluctuates. I am sure it's down to me not understanding all the features of the scope. Attached you will find the service manual instructions for the Sony.

Could anyone give me some tips to get a clearer steady wave form? Perhaps I need to reduce resolution or average the signal? Your help is much appreciated.
 

Attachments

Here's a photo of the wave form.
 

Attachments

  • IMG_20200407_142630.jpg
    IMG_20200407_142630.jpg
    838.5 KB · Views: 215
That's because the waveform isn't stable, not the 'scope. Have you tried a little switch-cleaner in the pots, they may be very dirty inside. Don't go crazy with it. If its not the pots then try a bit of tapping with an insulated stick to see if there's intermittency in any other components or solder joints.
 
The adjustment procedure assumes an analog scope, set at a low sweep rate to see the envelope of the signal.
You should activate the "digital phosphor", or "peak" or "envelope" mode on your scope to mimic that.

If the variations are too large, it would point to mechanical problem: something off-centered for example
 
That's why you need to average lots of different traces.
The acquisition/display modes on this scope model look scanty.
You could try the infinite mode, in free-running mode: trigger disabled or set to an unused channel:

attachment.php


You should see a band having a more or less homogeneous brightness, and the height of that band should be 6Vpp.

If you see too many irregularities, it probably means you have some kind of mechanical issue
 

Attachments

  • Rigol.png
    Rigol.png
    51.4 KB · Views: 192
I still think you have noise. I'm not familiar with the Rigol but my Tektronix has filters. Look for filters in the manual and give them a try.


Also are there electro caps in the circuit if so they might need replacing. I am not in the replace all caps camp, only the ones that are faulty.