Kg3v Ham Radio Blog

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Your Elecraft KAT-500 Tuner Protects your KPA-500 Amp - until it doesnt

Posted: 24 Jul 2019 06:16 PM PDT
https://kg3v.com/2019/07/24/your-ele...til-it-doesnt/


I have been using an Elecraft KPA-500 linear amplifier and a KAT-500
Antenna tuner with my Icom radios (mostly the IC-7600 and briefly with the
IC-7300) After much research and discussion, I figured out what I thought
was the best way to interconnect the IC-7600 with the KAT/KPA-500 so that
the Amp would be protected by the Automatic Tuner, in the case of antenna
problems. The Tuner was configured to know that it was being used with a
KPA-500. According to the Manuals, that means that in the event of any
antenna issue, the KPA-500 would be immediately disabled from transmitting.

I thought the key to this protection was to use the INHIBIT line from the
Tuner to unkey the Amp in the event of a Fault in the antenna or a bad
match on the Tuner for any reason. I connected it all, and began operating
with this setup. I worked a few contests using a Vertical, a ZS6BKW, and a
160m Dipole fed with Ladder Line. All seemed to be going well until

One night I was working a Contest and the Tuner started having problems on
80m CW using the 160 Dipole. I had used this before, so I kept retuning as
I moved up the Band, but something was wrong. The Tuner kept retuning when
I keyed the rig. Suddenly I smelled that awful well-known odor of burnt
electronics. I shut down the Amp and disconnected it, for further
investigation.
Damage to the Elecraft KPA-500 Amp

Testing showed that the AMP could be used on all Bands except 80 meters. On
80 meters, there was no power output that I could measure. I started
looking online and quickly determined that I had probably damaged
components in the 80 meter Low Pass Filter (LPF) on the RF/LPF module. I
began conversing with Elecraft about the possible damage. I must say that
my interaction with Elecraft was outstanding. They were very concerned
about my problem and helpful with the troubleshooting. We exchanged several
emails and they even sent me step-by-step instructions for making numerous
measurements on the RF/LPF module. This led to the discovery that the
270-volt line was dead, disabling the Power section when 80 meters was
selected.

I decided to remove the RF module to see if I could make a repair (some had
reported success in similar situations). Further online research uncovered
a detailed set of photos for disassembly of the AMP, and removal of the
RF/LPF module. This was incredibly helpful and saved me from several
potential mistakes. I successfully removed the module and could immediately
see the damage. There were a couple components that were obviously fried,
and a couple PC Board traces that did not look good.
Return the KPA-500 RF module to Elecraft for Repair

Elecraft offered to help me through the repair if I chose to do it myself.
We discussed several other options, including sending just the RF/LPF
module to them for repair. Since the damage was in a fairly dense section
of surface mount components and toriods, and I had no surface mount rework
equipment, I decided to let them do the repair.

I shipped the module to Elecraft. They had told me that the lead time might
be a couple weeks for the repair. After approximately that time period, I
received a phone call from the Technician at Elecraft that was doing the
repair. That was a shock! He said the repair was in progress, and he just
wanted to offer to discuss it. As I had a number of questions, I called him
and we discussed it for something like 20 or 30 minutes. This was extremely
valuable to me and again demonstrates how Elecraft goes above-and-beyond in
dealing with their customers.
Reassembling and Testing the KPA-500 NOT all Good News.

I received the repaired RF/LPF module and I could easily see the repairs.
They had replaced some Caps and repaired a couple traces on the LPF Board.
I installed the module and connected all of the wiring. When I connected
all of the equipment and keyed the Amp NOTHING happened. NO OUTPUT POWER!
Well this was disappointing. I thought I had probably failed in my
reassembly. I knew they had run a several-hour test and burn-in after
completing the repair. It turns out that there was still no 270-volts
present on the RF/LPF module.

Back to taking with Elecraft and searching the Web for answers. Apparently
there is a capacitor on this module that is known to fail in a mode that it
shorts when voltage is applied.Â* This appears to be a common failure. It is
possible that it has been remedied on newer Amps. My Amp was used and about
4-5 years old when I got it. Just my luck that it would fail now, just
after other repairs were done. I guess it could have happened in shipping.
Following Elecrafts instructions, I confirmed this was the failure.

Elecraft was as disappointed as I was. They offered to send me replacement
capacitors if I could make the repair. They also offered to fix it quickly,
at no cost, if I shipped it back to them. While I appreciated the offer of
the no-cost repair, I decided it was time to learn to do some SMT repair
work. We identified 2 capacitors that should be replaced. One was obviously
physically damaged and they recommended replacing the other one as well.
Both of the caps were fairly easy to access, so I was going to give it a
try. I got several of each; Elecraft had one value in stock and sent
several of them, and I bought the other one online at Digikey, opting not
to wait for Elecraft to get new stock.
Repairing the RF/LPF Module at Home

I found a very inexpensive SMT rework station online which is sold by a
number of Vendors. It got pretty good reviews, so I thought I would give it
a try. I had some old Computer boards that could be used to see if the
Rework Station and the Operator (me) were up to the task. The hot-air
worked fine for removing and attaching SMT capacitors. I did blow a couple
off the PC Board in the process from the moving air.

One of the first caps I had ready to put on the board was shot across the
room by my tweezers, never to be seen again. Fortunately both I and
Elecraft had provided multiple pieces of each capacitor. Finally I was able
to replace the small caps. I reassembled the Amp and measurements show that
all the necessary voltages are now present on the RF/LPF module.
Preparing to Use the Repaired Amp WHAT HAD HAPPENED??

This story is not over yet. The Amp is ready but I want to have a better
understanding of what happened, and must make sure there is no repeat
performance. There are several possibilities for the failure of he RF/LPF
module:

An antenna problem caused high and varying SWR that the Tuner could not
handle
RF was getting into the Tuner
There was simply a component failure it is known to happen


Due to the retuning that I saw just before the failure, I think there is a
good chance that my antennas and/or grounding were the culprit. I did find
a splice in my feedline that was near-failure and might have been arcing
when this happened. I also found that my station grounding is not good,
after reading several good articles on Grounding. Some antennas are very
close to my shack, and I will be taking some EMI/RFI mitigation steps in
the wiring.
Why did the Tuner NOT Protect the Amp?

This is the question that I still cannot answer. Reading the manuals, I
would have thought the Tuner would have quickly FAULTED and UNKEYED the
Amp. This damage looked to be caused by high voltages which I thought were
a result of high SWR between the Amp and the Tuner. Maybe my expectations
were too high. I will be much more careful in the future when using the Amp
and Tuner.
Final Outcome

I am still in the process of rebuilding antennas and Grounding. I will post
some follow-up comments, once I get everything assembled and try the Amp
again.

In article , rec-radio-amateur-
says...

I found a very inexpensive SMT rework station online which is sold by a
number of Vendors. It got pretty good reviews, so I thought I would give it
a try. I had some old Computer boards that could be used to see if the
Rework Station and the Operator (me) were up to the task. The hot-air
worked fine for removing and attaching SMT capacitors. I did blow a couple
off the PC Board in the process from the moving air.




Ebay has the rework stations for around $ 60 or so. Not very wxpensive
at all for a small soldering iron and hot air wand.

I did find that buying an Amscope micorscope for about $ 200 was a good
investment. The Amscope SE400 version with the 10x lenses are a good
place to start. The Z version comes with the 10 and 20 x if they have
not changed it.

If you get some Kapton tape and put it over the SMD area and just cut a
hole in it over what you want to replace, the hot air will not blow the
other components away.

Not conting a microscope you can get set up for SMD for about $ 100 to
$ 150 for the home hobby user. I was around 60 some when I started
working with the SMD and found it really easier than the other equipment
in many cases.

Get o youtube ans look at the videos and practice on some of the old
circuit boards first.