(fault now fixed – am copying to main Elecraft Reflector in case anyone else
has similar fault or further comments)
From: G3PQA
Sent: Friday, November 07, 2014 12:13 PM
To: ZL3IO [via Elecraft]
Cc: Gary Surrency, W3FPR, GM3SEK
Subject: Re: KAT3 Mistuning (in response to email from ZL3IO below)
Hi Holger,
Firstly, nice to work you on 80m cw recently and on 160m from ZL2IO!
My KAT3 mistuning symptoms were similar to those you describe, except it was
worse on the LF bands, improving and almost normal on higher HF bands.
My main wattmeter and swr functions appeared to be working, so the usual
suspects (swr bridge diodes D36, D37) did not seem to be the cause.
I would say that those diodes and associated components, and L10 C10 on the
KAT3 are the first things to check.
I was given very comprehensive (and as it turned out, good advice) from Gary
Surrency over what to look for (summarised below), but it did not fix the fault
initially in my case (perhaps because of multiple causes), I was chasing around
for ages.
1. To replace the swr bridge diodes D36, D37 (I used 1N5711 but the swr bridge
worked just the same so refitted the original smd diodes)
2. To re-fix all earthing screws and connectors around the LPA (3 screws
underneath), KAT3 and the SO-259 antenna sockets.
3. To check for dry joints or touching wires on the LPA HFP filters and KAT3.
4. To check filter L10 C10 on the KAT3 (8.215MHz IF trap, can be temporarily
shorted, only a parallel tuned circuit)
5. To check relay function if a specific band or bands (which does not appear
to be your fault)
5. After these checks and changes every time do a re-calibration (Wattmeter
and TX gain)
I did all this (but without re-cal every time), found no definite fault even
though it improved slightly, without a complete cure. It was still hunting. At
this stage I was thinking of sending the motherboard back to UK or USA but
reluctant to do this because of the trouble involved and I wanted to fix it
myself!
On checking further I looked at the swr toroids and found one (T3) where the
centre insulation was missing partly and the copper wire may have been touching
the ferrite – if so this could have caused an intermittent. I replaced the
small “U” wire with another using PTFE insulation.
Also I found correspondence relating to KAT3 earthing. (thanks to GM3SEK,
W3FPR, G3TJP and others). The KAT3 is earthed via a screw holding its pcb to a
hex pillar and 2D fastener to the side panel connected to the back panel, what
appears to be rather an indirect route. If any of these dis-similar metal
fixings go high resistance, or there is higher than normal RF induced in the
K3, then this may cause a problem. I fitted an extra 1mm flex wire on tags
between the bottom SO-259 bolt and the back of the KAT3 pcb. I cut the side of
the tag behind the KAT3 pcb to avoid a track which ran close, and used a new
nickel plated screw with very small flat washer to fix the pcb. Surfaces
cleaned and with thin layer of professional contact lubricant.
After re-calibration again the fault had gone!
Unfortunately because of its intermittent and non-precise nature, it was
difficult to pinpoint the exact cause. Possibly general deterioration via
several factors listed above ?
Am sure Elecraft support or others can either correct any errors above or
suggest other things to try in your case.
73 gl
John G3PQA
(K3 s/n 1123)
From: ZL3IO [via Elecraft]
Sent: Friday, November 07, 2014 3:47 AM
To: John G3PQA
Subject: Re: KAT3 Mistuning
Hi John
I have a similar problem on all bands. The antenna tuner worked nicely for many
years and now tunes everything worse. Antennas that are 1.5:1 get tuned into 4
: 1 no matter what band.
Got the advice to clean contacts which I did many time but nothing changed.
I'm not using the tuner anymore.
73 Holger
If you reply to this email, your message will be added to the discussion below:
http://elecraft.365791.n2.nabble.com/KAT3-Mistuning-tp7592847p7594461.html
To unsubscribe from KAT3 Mistuning, click here.
NAML
__
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Elecraft@mailman.qth.net
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to arch...@mail-archive.com
