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

Mon Mar 10 00:33:26 EDT 2014

An excellent, well-reasoned discussion.

73

Ken Kopp - K0PP
On Mar 9, 2014 10:23 PM, <maxwelltl at aol.com> wrote:

> 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 su
>  ch, 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
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