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KPA500 Question

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ws6x.ars

KPA500 Question

I just purchased a used KPA500 (SN 0456) from a close friend. The amp was
just back to the factory for several repairs and was thoroughly tested. The
report reads, "KPA500 #0456 meets or exceeds all factory specifications." My
friend unboxed the amp and made several QSOs to be sure all issues were
fixed. He then personally delivered the amp to my QTH.
Over the weekend I got the amp added to my operating position and was quite
surprised to find that input signals are attenuated significantly when the
amp is switched from STBY to OPER. No, this is NOT the issue with having the
aux cable and the PA key line connected at the same time. This is with NO PA
key, and NO aux cable connected. The amp has no connection but RF input and
output. It is independent of band. This is with a matched antenna, band
switched manually with the front panel buttons. When I engage OPER the input
signal is attenuated by ~20 dB.
On the TX side, the amp is fine. On most bands I get full rated output into
a dummy load with approx. 20 Watts of drive from the K3.
I noticed on the service report, one of the tests was, "Tested receive
attenuation and IMD." I'm curious about "receive attenuation." This would
seem to be related to my problem. Looking at the block diagram, I surmise
something in the TR switch is malfunctioning.
Before I bug an already-overloaded Elecraft support, I am open to
suggestions. Am I missing something obvious?
TIA es 73,
Jim - WS6X
P.S. Yes, I have read the manual, and scoured the archives. The only thing I
can find regarding input attenuation in the OPER mode involves incorrect
cabling.

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ANDY DURBIN

KPA500 Question

" When I engage OPER the input signal is attenuated by ~20 dB."

I can detect no difference in received signal between OPER and STBY. This was for an "on air" test. I did not test with a signal generator.

Andy, k3wyc
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Mark Goldberg

Re: KPA500 Question

In reply to this post by ws6x.ars

Is the key line indication on all the time? This may be indicative of a
stuck key line. There was an unsoldered resistor on mine causing the issue.

73,

Mark
W7MLG

On Sun, Apr 18, 2021, 2:38 PM <[hidden email]> wrote:

> I just purchased a used KPA500 (SN 0456) from a close friend. The amp was
> just back to the factory for several repairs and was thoroughly tested. The
> report reads, "KPA500 #0456 meets or exceeds all factory specifications."
> My
> friend unboxed the amp and made several QSOs to be sure all issues were
> fixed. He then personally delivered the amp to my QTH.
> Over the weekend I got the amp added to my operating position and was quite
> surprised to find that input signals are attenuated significantly when the
> amp is switched from STBY to OPER. No, this is NOT the issue with having
> the
> aux cable and the PA key line connected at the same time. This is with NO
> PA
> key, and NO aux cable connected. The amp has no connection but RF input and
> output. It is independent of band. This is with a matched antenna, band
> switched manually with the front panel buttons. When I engage OPER the
> input
> signal is attenuated by ~20 dB.
> On the TX side, the amp is fine. On most bands I get full rated output into
> a dummy load with approx. 20 Watts of drive from the K3.
> I noticed on the service report, one of the tests was, "Tested receive
> attenuation and IMD." I'm curious about "receive attenuation." This would
> seem to be related to my problem. Looking at the block diagram, I surmise
> something in the TR switch is malfunctioning.
> Before I bug an already-overloaded Elecraft support, I am open to
> suggestions. Am I missing something obvious?
> TIA es 73,
> Jim - WS6X
> P.S. Yes, I have read the manual, and scoured the archives. The only thing
> I
> can find regarding input attenuation in the OPER mode involves incorrect
> cabling.
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>

Thomas Kluge-2

Re: KPA500 Question

In reply to this post by ws6x.ars

Hi Jim,

Sounds like an issue with the T/R circuit, you'll find some reports in
the history of this list. I had a very similar case just one week ago -
in my case it was R7 which was blown. The original type seems to be a
51 Ohm (type 1206 SMD) resistor - I've used now two 100 Ohm 1/4 watt
resistors in parallel... Please check the diodes D8 and D9 if the
resistor is ok - but in my case it was very obvious: At least I've seen
the remainders of the SMD and not just a black spot (as others reported
earlier)...
Taking the PA apart and put everything back together took more time
than the repair ;-)

Best regards
Tom, DL3DTH

Am Sonntag, dem 18.04.2021 um 17:36 -0400 schrieb [hidden email]:

> I just purchased a used KPA500 (SN 0456) from a close friend. The amp
> was
> just back to the factory for several repairs and was thoroughly
> tested. The
> report reads, "KPA500 #0456 meets or exceeds all factory
> specifications." My
> friend unboxed the amp and made several QSOs to be sure all issues
> were
> fixed. He then personally delivered the amp to my QTH.
> Over the weekend I got the amp added to my operating position and was
> quite
> surprised to find that input signals are attenuated significantly
> when the
> amp is switched from STBY to OPER. No, this is NOT the issue with
> having the
> aux cable and the PA key line connected at the same time. This is
> with NO PA
> key, and NO aux cable connected. The amp has no connection but RF
> input and
> output. It is independent of band. This is with a matched antenna,
> band
> switched manually with the front panel buttons. When I engage OPER
> the input
> signal is attenuated by ~20 dB.
> On the TX side, the amp is fine. On most bands I get full rated
> output into
> a dummy load with approx. 20 Watts of drive from the K3.
> I noticed on the service report, one of the tests was, "Tested
> receive
> attenuation and IMD." I'm curious about "receive attenuation." This
> would
> seem to be related to my problem. Looking at the block diagram, I
> surmise
> something in the TR switch is malfunctioning.
> Before I bug an already-overloaded Elecraft support, I am open to
> suggestions. Am I missing something obvious?
> TIA es 73,
> Jim - WS6X
> P.S. Yes, I have read the manual, and scoured the archives. The only
> thing I
> can find regarding input attenuation in the OPER mode involves
> incorrect
> cabling.
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

marvwheeler

Re: KPA500 Question

In reply to this post by Mark Goldberg

What happens if you reduce the rf output on the k3 to some value below 12
watts. I have the same symptoms and thought it was the KPA500 but after
disconnecting the K3S from the rest of the station I accidently determined
that if I decreased the RF output to less that 12 watts the receiver is no
longer attenuated. I am waiting until Elecraft is on a more normal footing
before sending it back for repair.

Marv
KG7V

-----Original Message-----
From: [hidden email] <[hidden email]> On
Behalf Of Mark Goldberg
Sent: Sunday, April 18, 2021 3:20 PM
To: [hidden email]
Cc: Elecraft Mailing List <[hidden email]>
Subject: Re: [Elecraft] KPA500 Question

Is the key line indication on all the time? This may be indicative of a
stuck key line. There was an unsoldered resistor on mine causing the issue.

73,

Mark
W7MLG

On Sun, Apr 18, 2021, 2:38 PM <[hidden email]> wrote:

> I just purchased a used KPA500 (SN 0456) from a close friend. The amp
> was just back to the factory for several repairs and was thoroughly
> tested. The report reads, "KPA500 #0456 meets or exceeds all factory
specifications."

> My
> friend unboxed the amp and made several QSOs to be sure all issues
> were fixed. He then personally delivered the amp to my QTH.
> Over the weekend I got the amp added to my operating position and was
> quite surprised to find that input signals are attenuated
> significantly when the amp is switched from STBY to OPER. No, this is
> NOT the issue with having the aux cable and the PA key line connected
> at the same time. This is with NO PA key, and NO aux cable connected.
> The amp has no connection but RF input and output. It is independent
> of band. This is with a matched antenna, band switched manually with
> the front panel buttons. When I engage OPER the input signal is
> attenuated by ~20 dB.
> On the TX side, the amp is fine. On most bands I get full rated output
> into a dummy load with approx. 20 Watts of drive from the K3.
> I noticed on the service report, one of the tests was, "Tested receive
> attenuation and IMD." I'm curious about "receive attenuation." This
> would seem to be related to my problem. Looking at the block diagram,
> I surmise something in the TR switch is malfunctioning.
> Before I bug an already-overloaded Elecraft support, I am open to
> suggestions. Am I missing something obvious?
> TIA es 73,
> Jim - WS6X
> P.S. Yes, I have read the manual, and scoured the archives. The only
> thing I can find regarding input attenuation in the OPER mode involves
> incorrect cabling.
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net Please help support this email
> list: http://www.qsl.net/donate.html Message delivered to
> [hidden email]
>

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ws6x.ars

Re: KPA500 Question

In reply to this post by ANDY DURBIN

"When I engage OPER the input signal is attenuated by ~20 dB."

Thanks to all for the prompt and informative replies. Apparently the culprit
has been found. Several reported the exact same issue, one as recently as
one week ago. According to one reply, an Elecraft Tech told him, "This is a
known failure mode." (Not very encouraging!)
Here is a copy of an Elecraft repair report:

Reported problem(s):
Receive signal is attenuated when in operate. Receive signal is normal when
in standby.

Problem(s) found:
Confirmed problem. Found that D8, D9 and R7 in the T/R circuit had failed.

Repair(s) performed:
Replaced D8, D9, and R7 on the LPF board.

Looks like my KPA500 is in for some "belly up" treatment!
One thing has me a bit puzzled though. If this is a known weakness, why
hasn't Elecraft designed a "beefed up" mod? My amp had 5 updates / mods done
while it was at the factory. This "known failure" was not one of them.
Thanks again, for all the help!
Jim - WS6X

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KENT TRIMBLE

Re: KPA500 Question

Just because a tech says it's a known failure today doesn't mean it's
been a known failure throughout its production run. Component
availability and sourcing necessarily change over the years. A robust
component from a former supplier ten years ago may not be as robust from
a different supplier today. There is no way of knowing which components
exhibit early failures until they fail early.

Consider yourself now an experienced beta-tester!

73,

Kent K9ZTV

On 4/18/2021 6:59 PM, someone wrote:
> According to one reply, an Elecraft Tech told him, "This is a
> known failure mode." ... If this is a known weakness, why
> hasn't Elecraft designed a "beefed up" mod?

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ws6x.ars

Re: KPA500 Question

Point taken.
FWIW: This "known failure" tech comment was in 2018.
Jim - WS6X

On Sun, Apr 18, 2021, 8:33 PM KENT TRIMBLE <[hidden email]> wrote:

> Just because a tech says it's a known failure today doesn't mean it's
> been a known failure throughout its production run.
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Iain MacDonnell - N6ML-2

Re: KPA500 Question

In reply to this post by ws6x.ars

On Sun, Apr 18, 2021 at 5:02 PM <[hidden email]> wrote:

>
> "When I engage OPER the input signal is attenuated by ~20 dB."
>
> Thanks to all for the prompt and informative replies. Apparently the culprit
> has been found. Several reported the exact same issue, one as recently as
> one week ago. According to one reply, an Elecraft Tech told him, "This is a
> known failure mode." (Not very encouraging!)
> Here is a copy of an Elecraft repair report:
>
> Reported problem(s):
> Receive signal is attenuated when in operate. Receive signal is normal when
> in standby.
>
> Problem(s) found:
> Confirmed problem. Found that D8, D9 and R7 in the T/R circuit had failed.
>
> Repair(s) performed:
> Replaced D8, D9, and R7 on the LPF board.
>
> Looks like my KPA500 is in for some "belly up" treatment!
> One thing has me a bit puzzled though. If this is a known weakness, why
> hasn't Elecraft designed a "beefed up" mod? My amp had 5 updates / mods done
> while it was at the factory. This "known failure" was not one of them.

There definitely has been "beefing up" of the T/R circuit over the
years. I don't know about dates.

You might find this interesting (although I think your failure is
different - I've been "lucky" enough to experience both, and more):

http://ok1rp.blogspot.com/2017/02/elecraft-kpa500-lpf-tr-switch-rework.html

Mine when back in late 2019, and had the following performed (amongst
other fixes and updates):

"Replaced Q5, D7, R3, R9 and R24 for Transmit/Receive MOD (Improves
robustness in Transmit/Receive circuitry)."

Good luck getting a response from Elecraft support now. Apparently
they don't respond to email any more (mine from April 5th has been
ignored so-far, and I've seen similar reports from others here).

73,

~iain / N6ML
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