Thanks Lawrence.?
Evan, the Si5351 breakout board has short leads and is nearly on top of where the 5351 used to be on the main board. Please see the photo. Also, the cable to the RTC board already has chokes per your previous suggestion. For the purposes of this testing the RTC unit itself is not connected.
I now have a half decent scope which is light years more useful than the cheap scope I had been using. I can now clearly see what¡¯s on the I2C lines and store images. It¡¯s much easier to see clearly whether there should activity or not. Same goes for the clock outputs.?
Here¡¯s what I¡¯ve seen tonight: the Si5351 breakout board appeared dead, or was not active, for days regardless of restarting the sBitx process or rebooting the unit or recycling power. Previously in weeks past it apparently wouldn¡¯t start and the waterfall would run but without any signal or noise whatsoever, and there was no rf output on key down. Tonight, however, that inactivity once again became intermittent. It happened about three times but came completely back to life with a power recycle. And later on it became more stable, reliably starting up with good audio, good FT8 signals and good CW output to a dummy load. So the board is not fried. ?Why it¡¯s intermittent is a mystery. I¡¯ve checked all of the solder connections and they look fine but perhaps I should reheat each joint in case there¡¯s a cold one. This is with the front panel and RTC clock removed.
Now that I have a scope that¡¯s easier to use I can see more clearly (with better triggering circuits) when there is activity on SDA and SDL, and output on the clock outputs. See the stored traces that I uploaded. First, there¡¯s a signal on the I2C lines even when the main power is off, and this is clearly present only when the HDMI is connected to the Raspberry Pi. Next are the traces from the SDA, SCL and CLK0 CLK1 and CLK2 lines. When the sBitx process is running but there¡¯s no audio or waterfall noise or signal, there¡¯s no activity¡ªnothing¡ªon the I2C lines and no clock output at all. I am not sure why I am having this intermittent problem but at least it¡¯s working now. I wonder whether there is a problem with one of the pull-up resistors on the Adafruit Si5351a breakout board. I could always reinstall the pull-up resistors on the main board which are sitting there tombstoned. I also put some heat sinks on the 2N2219A¡¯s. They were getting hotter than the IRFZ24Ns! I¡¯ll take a closer look tomorrow.
73
Jack?
N6LN
John Terrell, N6LN