开云体育

I've finished a v5.2 board and the VNA seems to be operating properly.? However there was one odd observation that I was hoping someone in the group may have seen before, or have a theory about.

The 3.3V regulator that feeds the CW master osc shows 3.3V **without** the CW MO connected.? With the CW MO connected, the 3.3V terminal reads about 3.55V.? Roughly 0.25V high.

Notes:

1. The voltage tracks the 5V rail.? If the 5V rail is set to 5.1V, the observed voltage is higher yet, about 3.6V.

2. The regulator is not oscillating.? I have measured the voltage at the terminal with 2 HP lab DVM, a fluke, an oscilliscope and a SA.? There is some level of the 156 Mhz present on the +3.3V line, but I'm not sure if that's just being picked up by the near proximity of the oscillator's ajacent output.? I've replaced both the 0.1 & 10 uF caps ajacent the CW osc just for good measure.

3. The VNA seems to work fine with as-expected noise floor levels.

4. While the CW part is a 3.3V nominal, the abs max voltage is 5V so even if the circuit is truly running at 3.55V, the oscillator is probably not in mortal peril.

5. Checks of nearby points show nothing in the 3.55V or 0.25V range.

6. With the +3.3V feed from the regulator pulled, the voltages around the CW osc are all zero.

7. The CW oscillator output is clean and stable.? I can see 2nd/3rd harmonic levels but it looks like it's working fine.

8. Current consumption of the oscillator is about 30 mA which I think is in line with the datasheet values.

At the moment I have no explanation for this.? Hoping someone would have a theory.? Or be able to check their board and see if they have a similar observation on the MO voltage.

73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com

Sounds like the gnd terminal of the regulator is floating. Mine behaved normally.

Gary NA6O

Thanks Gary.

Unfortunately it shows solid continuity when I test it.

I have replaced the regulator as well - the replacement and the original behaving the same, unfortunately.

73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com