[HighAltitude]

In the process of setting up my Telemaster fixed wing system, I lost communication between my OPLink mini serving my ground station and the Revo board on my aircraft.  After flailing around for more time than I should have checkin/resetting the communication parameters on the OPLink tab on configuration, checking that the firmware versions were compatible, etc. etc., I finally tried it with one of my quads.  Lo and behold, it connected with -16 dB signal strength. The OPLink Receiver settings are the same for both Revo boards.
I think I've been compulsive about making sure there was an antenna connected to my Revo board before I've powered up from either the receiver (PWM) or USB connection, but may have forgotten to reconnect it sometime during my machinations.
Everything on the Revo board in the Telemaster seems to work properly when it's connected to the GCS via the USB cable.
Is there a way to determine if the transmitter on the Revo board has been fried?

[TheOtherCliff]

What RF power level did you have the Revo set to?

In my own experience, I ran a quad for a while that had a loose Revo antenna.  I only had it set up for telemetry.  When I later found that my logging range was very short, the antenna was completely disconnected at that point.  I reconnected it and got back the full range with everything OK.  Just offering a data point that they don't have to always burn up.  I recall that I was running 50mW.

The non-coordinator end (the Revo) will never transmit until it hears the coordinator poll it for data, configuring it to talk to a known working GCS-OpLink is the easiest way to test.

I would also check the antenna connectors.  In particular, disconnect them and look at them with a magnifying glass.  Try the known good antenna with the questionable Revo.

If you have the same software/firmware version on OpLink, Revo, and GCS, then it should work.  There are cases where they don't have to match, but start with them all matching is easiest.  I am assuming that you are very familiar with the OpLink settings that must be made to get it working.  GCS is oplinkcoordinator, quad is oplinkreceiver.  Data, Control, or DataAndControl must be set the same on both sides.  Device ID on coordinator side must be typed into the receiver side.  Max chan / min chan's must match.  Max power must be non-zero on both sides.  Com speeds must match.  Leave the other stuff set to default.

I would start by saving settings for working boards (for instance your working quad), because this testing will erase them.  Beware that you should save and restore settings via USB, not via OpLink RF because, some versions of LibrePilot save the GCS OpLink settings, not the airborne Revo-Oplink settings, when you try to save the aircraft settings via OpLink... 

Do upgrade and erase on the working Revo board.  Do a quick setup to the point where you can test the RF connection.  Do the same thing with the questionable Revo board.  If the good board works with this complete reset, but the bad one fails, you know you have bad hardware.

It is possible that the Revo-OpLink can receive but not transmit.  In that case, it can actually still be used for control, but not for data.

[karla]

In my experience, there have been several cases where different editions/makers of the oplink units don't talk well to each other but fine with others. By trial and error I found pairs that works fine together.

[HighAltitude]

1. RF is set at 100 and data only.
2. After a couple of days of letting the Telemaster project lie fallow, I set up my bench testing rig again this morning, connected everything and powered up.  The OPLink and Revo were talking to each other with an indicated -22 dB signal strength. 
Insofar as I can remember, I didn't change any parameters on the OPLink, the Telemaster or the quad Revo boards before testing with the quad. 
Regardless, since all my vehicles are again communicating with my ground station, I can move on to trying to get two of my Revos to recognize the mag sensor in the uBlox Neo M8N modules to which they're connected.
Thanks again to TheOtherCliff and karla for the input.   

[trust]

As I recall I had issues with different units and it turned out to be the antennas - some antennas did not work at all or poorly on some units. I ended up testing a bunch of antennas and found ones that seemed to work well on all the units I tested (4 or 5).
I could also "detune" antennas by placing bits of foil wrapped around and moved up and down and improved antennas that didn't work well. But it was not a very good solution - I only recommend it for a temp fix.