Quote:
Originally Posted by old_tv_nut
Can you check with a scope set to DC coupling or maybe just with a voltmeter whether the VA62 output runs negative from ground (like the regular C1 voltage) or floats around zero?
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In short there is no DC voltage offset from the VA62. As I look over the schematic it looks like everything that gets signal from test point C1 is capacitively coupled so does the DC offset even matter? Now for more details I Took some measurements from both the VA62 feeding the RF generator into the tuner, and then also the VA62 injecting composite video (currently at L5 & C18 with the diode lifted).
Using the tuner:
- C1: -2.97 Volts DC
- C1: 0.25 Volts AC
Injection:
- C1: 0.043 Volts DC
- C1: 0.25 Volts AC
- Note I did adjust the VA62 signal amplitude up to match the 0.25 Volts AC
- Note the scope pictures are with DC coupling and no changes were made other than adjusting the trigger to get a clear waveform.
- Note with the tuner still tuned to the RF generator which is sending a blank signal I can kind of get the picture to sync, when I turn the tuner to an empty channel the sync from injecting is very scrambled.
- Note due to the camera shutter speed the below image looks way better
