Sick Radioberry board and TVS diode D401

[Jack KD4IZ]

Trying to troubleshoot a sick Radioberry Board. The tuned frequency is received but with large sensitivity loss and apparent junk signals getting through the antialias filter with the .

If the TVS diode D401 in the RX input circuit (between the antialias filter and T402 fails (after static/transient?) could that result in a significant reduction in sensitivity and loss of some of the alias blocking?

If that is unlikely, would that indicate that AD9688 RX + and RX- (pins 37/38) input is damaged but otherwise chip is working?

I would think that if AD9688 were damaged I would have no signal at all.

TIA for any assistance interpreting these findings.

--
Jack
KD4IZ

[Rick Koch]

Hi Jack,

An easy thing to try, depending on your soldering skills, is to lift one led

of D401. If it's defective/damaged you should see your signals come back.

-Rick / N1GP

[Jack KD4IZ]

Rick,

Thanks, I’ll give it a try.

Jack - KD4IZ

[Jack KD4IZ]

Rick, All,

Well, I had no problems with the soldering, have a rework station, but a quick tap with desolder ribbon on each end and the diode came right off. The signal issues did not change, so I conclude that I somehow damaged the front end on the AD9688BCP chip. Signals registering S9+20 on the other Radioberry board I have barely read S3 and there is lots of hash plus periodic (about 10KHz apart) birdies on the pihpsdr waterfall. I priced an AD9866 and (even from Shenzen) the price plus shipping is almost half the price of the board. This board is a scrapper unless someone has a spare ADC chip they want to part with.

The good board is now stacked with the "preamp" board and the Juice. Using a buck converter board to limit supply voltage to the preamp board to 7.5V. Little system works like a champ, so now waiting for a 4X4X4 extruded aluminum Hammond box to put it in. It will be mounted on a piece of circuit board in the case with all important leads to external connectors. Also have a small muffing fan that will mount in the space. Figure heat dispersion could be critical without the fan.

I have been running the stack with Thetis and the both transmit and receive performance is impressive for what it is. The learning curve with Thetis is a little challenging, but there seem to be plenty of online resources to extract useful info from.

Thanks for answering!

Jack Spitznagel
KD4IZ FM19oo
Parkton, MD