[Skimmertalk] QS1R rescue - almost there... But not quite

[Jeff Blaine]

I've been working on a QS1R and have it mostly operational. 
Unfortunately in the case of an SDR, "mostly" also means "not yet" 
operational from a "does it do something useful" standpoint.

Wanted to see if anyone had any comments on the symptoms observed.  At 
this point I'm out of ideas...

Background:  The unit was subjected to reverse voltage and was thought 
to be operational.  There was shipping damage with some 
adhesion-attached heat sinks coming loose in transit and banging around 
in the box enough to knock a couple of the larger electrolytic loose.  
The reverse protection diode had exploded but the voltage regulators are 
all operational and functioning correctly.  physical component damage 
has been repaired with replacement caps and a close examination for 
physical damage under magnification has been performed.

General operation - current draw are consistent with an operational 
unit; several hundred mA at idle, and about 1.3A with Skim Server 
loaded, without a big spot loading.  Voltages on the several regulators 
are stable and noise levels are the same as the operational unit.  
Heating and cooling and flexing the board shows no impact to the 
operational status.

On the chance that the often cited USB chip was at fault, I did manage 
to replace it (which initially was "how hard can that be" only later to 
become "I'll never do THAT again...") with no change in board behavior.  
So that's not part of the problem.

LED:  In the operational unit, LED D2 (LED most near the board edge) is 
lit, and adjacent LED D3 (2nd from the edge) is not lit. But in the 
defective board, LED D3 is lit as well as D2.  This is the only visually 
observable difference seen.  Power LED is on, CLIP light is off as 
normal.  From the VERB manual, I think the illumination of D2 means 
"program loaded" (VERB manual, page 14). This seems to imply that the 
FPGA and the USB are in fact functional, at least from the ability to 
handle USB transactions and get the FPGA loaded.

Further on the CLIP led.  I was thinking maybe the ADC function could be 
established using the CLIP as an indicator of overload so that I would 
know the ADC is doing it's thing.  However I could not get a CLIP 
indication with even +15 dBm on the board which caused me to think maybe 
the ADC was dead.  Unfortunately this is not conclusive as on the 
operational (known good) unit, the CLIP indication does not fire either 
at this level and given the cost of the ADC, I'm not interested in 
possibly destructive testing of the ADC...  So for now, I'm assuming the 
ADC is working although that's a stretch.

External clock:  both units are configured for external clocking.  This 
provides an additional diagnostic via the CLIP LED.  When an application 
is loaded, and there is no clock signal, the CLIP light will light.  
With the clock signal connected, the CLIP light extinguishes.  This 
behavior is the same in both the operational and defective unit.  I'm 
assuming this means the ADC is at least somewhat operational as the CLIP 
light is run directly by the ADC.

Running Skim Server, the USB device shows up in device manager. The FPGA 
loading window comes up and completes, and skimmer opens.  Then skimmer 
toggles between "SDR RECEIVER OK" and "SDR_FAILURE: USB_BULK_READ 
FAILED" on a several second basis. From a prior post, there was a 
comment about the voltage regulators cutting out and causing this effect 
but monitoring the regulators at the time this is occurring shows stable 
power on all regulator outputs.

Running the QS1R SDR app, the server applet loads with success. The GUI 
loads as normal.  But when RUN is clicked, there is no further response 
by the app.

Appreciate any advice or insights from guys who may have been there, 
done that and got their QS1R to rock and roll for another day.  Thanks!

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