[Elecraft] REF: KXPA100 SN 707 Total Frustration with this Amp

[maxwelltl at aol.com]

Hey Rich, 


Problems like these can be very frustrating.  Not lecturing to you, but take a deep breath.  You will get it going.  I know the tendency is to throw the baby out with the dirty diaper (or however that saying goes) but from my experience and what I am reading we have a very good amp in the KXPA100.  I started my career in electronics 42 years ago and 9 times out of 10 the reason for a problem is really quite obvious - once it is fixed that is. :)




I don't see where the schematic and firmware is available for the KXPA100.  It may be, I just don't see it.  But lets do some logical troubleshooting.  First, the front plate and the nut have nothing to do with the operational problem.  Granted, it shouldn't have happened but it did.  Elecraft made good on it so that one is no reason to be talking about returning the amp.  The two are simply not connected.  I will say that I had parts problems with mine also - not Elecraft's but my bone-headed failure to read the Eratta.  I twisted off a standoff lug.  Elecraft sent me a new one.  And guess what, I wasn't really short lock washers either, I just didn't read the part that said I didn't need them under the standoffs.  Duh!  So it sounds like your parts situation is OK now.


So, the KX3 seems to work fine going around the amp.  That tells me your problem is definitely in the amp.  OK you knew that.  But there is no need to be changing out the tuner and what not.  The problem is in the KXPA100.  I buy that.  It appears the KX3 is talking to the KXPA100 just fine.  It recognized it and adjusted itself for proper power etc.  That is an RS232 serial interface so there isn't much that can go wrong with it.  All of the data goes down 1 wire.  Unless it intermittently and randomly just starts switching or tuning or changing something, I wouldn't suspect the RS232 link.  It should either work (as it appears to be doing) or it doesn't. So there is no need to mess with that interface. 


The SWR of 99.9 is probably not so puzzling when you think about it.  What would happen if you didn't have any antenna connected?  Or if the antenna connector or cabling were shorted?  In theory, the SWR would be infinite.  But I suspect the firmware in the amp can't handle infinite SWR too well.  So I am guessing that when SWR goes over a particular limit it just says, "The SWR is too freekin high.  I am just going to display 99.9 to tell the user it is way out of wack."  I suspect that what is happening is that your antenna is not really connected to the radio when you think it should be.  If your amp is seeing an open antenna line when it tries to transmit, you should see what you are getting.  Now stick with me.  The fact that you are seeing some weird switching indications between ANT1, ANT2, and Bypass, tells me that you may have your coax connectors inside the amp connected to the wrong receptacles on the board.  I don't know how that would effect the LED lights and such, but it could sure mess up operations.  Ask me how I know?  When I first powered mine up, I noticed the KX3 was very very quiet.  More so than it should be.  So I started playing around and discovered that when I connected my antenna to the ANT2 connector I got an increase in noise.  HMMM!  Switch to Antenna 2 on the KX3 and the noise drops to nothing.  Move the antenna cable over to the ANT1 connector and it comes back.  I had crossed the ANT1 and ANT2 connectors when I plugged them into the board.


Now in your situation, you may have something similar.  I don't know what the switching circuits and relays all look like in there, but it appears that your problem could be similar.  There is one symptom you mentioned that I can't answer.  You said you were getting 30 or 40 watts out of the big amp instead of 300-400.  I don't understand that.  If the RF drive is not going into the amp, I would say you should get zero output.  Maybe there is something going on there with keying the amp with no drive that would cause some strange meter readings.  Or maybe the coax cable in your KXPA100 is partially open or shorted.


Anyway, I would open up the KXPA100 and double check those connectors to be sure they are plugged into the appropriate sockets.  You could also get an infinite SWR if a cable were almost fully shorted.  Check for that also.  Also check to make sure you didn't flex the cables so much that one broke off the back of the SO239 connector.   Finally, double check to make sure that when you plugged in the tuner board you didn't bend or miss a pin in one of the connectors.  Just triple check, I know you have double checked.  Then hook up your antenna again to the KXPA100 (the big amp isn't needed for this troubleshooting) and use the listen test I mentioned earlier.  You should be able to tell pretty quickly if you have a good path between the antenna and the radio through the KXPA100.  You should then be able to switch antennas and tell that everything is hooked up cleanly and you have good paths and everything is switching properly.  Having a dummy load to test with is a good idea but you shouldn't need it until after the listening test.  Finally, if all is OK and you still can't find anything, it may be time to send it back for a look see.  Contact Elecraft and they  may have more ideas, but I bet they will works something out with you if it can't be resolved over the phone.


Good luck and let us know what you find.  My money is on something simple only because I have made so many mistakes in my career that I have learned to trust the equipment and look at myself first.  If I had a nickle for every time something worked worse after I worked on it than before, I would be rich!  Hi!  Keep your chin up and keep on keepin on.  Let us know how it goes, please.


73,


Tom/AE5QB