[DSP-10] Resolved - the DSP-10 problem!

[Don AE5K]

I am happy to report my DSP-10 is now putting out approximately 13 mw  ( 
+11 dbM ) and I believe we found the cause of the power jump intermittent.

Today, as previously planned, I brought my DSP-10 and instrumentation to 
Gary K5QNM's residence (50 mile drive) and we both worked on it trying 
to first find the source of the intermittent and secondly to see what we 
could do to increase the power output from about +3.6 dBm. It pays to 
troubleshoot with an extra pair of eyes present along with a 2-way 
discussion in real time.

While looking for poor solder joints or other problems around the 
transmit chain (U4-U5-Q2), we had the DSP-10 turned on but in receive 
mode at one point, and Gary was moving the multicolored short ribbon 
cable (at least on my TAPR kit) to get a better view when we heard a lot 
of scratchy static on the speaker.  Ah-ha!  Removed power and I tried to 
remove J5 at the end of this cable going to P5 on the main board.  In so 
doing, the wire ends came right out of the connector!  J5/P5 contains 
the following signals from the DSP box: ADC-L, GND, ADC-R, DAC-L, GND, 
DAC-R.

Further investigation showed that my "crimp" job of those 6 conductors 
left an awful lot to be desired.  Instead of re-crimping, Gary soldered 
the connector parts and I re-installed the connector and the DSP box.

That did it!  The power was actually the same as before the discovery, 
but we think that was the cause of the power jumping lower at times.  I 
might add that before this wire pull-out happened, the sidetone on 
transmit seemed much weaker today than in the past.  After repair, there 
was NO SIDETONE!

We went ahead and with makeshift coil core tuning tool, managed to go 
thru L8 thru L12 peaking for maximum transmit power.  (This had been 
done once the other day)  The end result: +11.1 dBm (13.1 mw) but still 
no sidetone at all.  I had only the mono unpowered speaker connected 
thru a mono jack. [Note: later at home, at cold start power measured 
+11,2 dBm 13.8 mw.)

Upon returning home, I re-setup the DSP-10 and added a pair of powered 
stereo speakers with the stereo 3.5mm jack.  Voila!  Nice sidetone in 
the right speaker.

I've not checked out everything, but I have confidence we found the real 
problem. The only mystery in my mind remaining is why previously we 
heard the sidetone on the mono connected speaker and after the fix only 
could hear it on a stereo connected speaker.  I know the sidetone is 
only produced on one channel, but what wire failure would cause the mono 
to work before the fix?

I would like to thank Mike KD5TS who once again came to my rescue (we 
had some previous correspondence a year or so ago too) and for sticking 
with me on this.  And to all the rest of you who contributed 
suggestions.  And to Gary K5QNM who assisted me today.  It is all 
sincerely appreciated.

Now, onward to getting an old NTMS (North Texas Microwave Society) 1296 
transverter back to working condition plus power amplifier that will 
allow me to eventually put out about 15 watts on that band.  I'm ashamed 
to admit it, but Gary and I have been at this 1296 project for over FIVE 
years now and I expect very soon we'll easily cover our 32 mile as the 
eagle flies path.  A rovering I shall go!

73,
Don AE5K
EM36pc Marion County, northern Arkansas