100 watt PA issue


Jeffrey griffin
 

Last summer I was running more data modes (FT8) when I started having an issue with the 100 watt PA failing with a ERR 12V message. I then did the KP3A power connector replacement. This worked fine for a few months. It was working fine till I once again noticed a strong burnt electronics smell coming from the K3's PA. I at that time just used it at 12 watts to Drive the KPA500 for a while as this worked fine. Today I decided to take it apart and try to determine what the issue is. After removing the KP3A module I noticed that L23 on the main board is severely heat damaged. I wasn't expecting this, I was looking to inspect the power connector that I had fixed with the gold pins 6 months ago. Anyone have any thoughts on why L23 would fail? Before I send it to Elecraft. Thanks...

73 Jeff kb2m


john ni0k
 

Running 12 watts on data modes is bad. The low power PA won't withstand that.

-de John NI0K

Jeffrey griffin wrote on 5/3/2020 12:35 PM:

Last summer I was running more data modes (FT8) when I started having an issue with the 100 watt PA failing with a ERR 12V message. I then did the KP3A power connector replacement. This worked fine for a few months. It was working fine till I once again noticed a strong burnt electronics smell coming from the K3's PA. I at that time just used it at 12 watts to Drive the KPA500 for a while as this worked fine. Today I decided to take it apart and try to determine what the issue is. After removing the  KP3A module I noticed that L23 on the main board is severely heat damaged. I wasn't expecting this, I was looking to inspect the power connector that I had fixed with the gold pins 6 months ago. Anyone have any thoughts on why L23 would fail? Before I send it to Elecraft. Thanks...

73 Jeff kb2m 






Jeffrey griffin
 

I remember all of this now. Actually  I was running about 7 watts to drive the AMP after I had the PA failure at 100 watts, there were no issues at 7 watts. I was trying to make the point that I was avoiding the 100 watt PA by running under 12 watts. Sorry for the confusing first email. This all happened in October while I was still at my summer home. Been awhile, I just got around to working on this here in Florida today. Use my Flex 6500 here and the K3 sat since November as I use it just in NJ but brought it here to work on.

 So to clarify the problem was at 100 watts or so while running data modes, SSB QSO’s were no issue. Data contacts at 7 watts to drive the KPA500 was also no problem. I never had a problem with my K3 since 2007 until last year or so with the more frequent data mode duty cycles

 

73 Jeff kb2m

 

From: Elecraft-K3@groups.io <Elecraft-K3@groups.io> On Behalf Of john ni0k
Sent: Sunday, May 03, 2020 17:59
To: Elecraft-K3@groups.io
Subject: Re: [Elecraft-K3] 100 watt PA issue

 

Running 12 watts on data modes is bad. The low power PA won't withstand that.

-de John NI0K

Jeffrey griffin wrote on 5/3/2020 12:35 PM:

Last summer I was running more data modes (FT8) when I started having an issue with the 100 watt PA failing with a ERR 12V message. I then did the KP3A power connector replacement. This worked fine for a few months. It was working fine till I once again noticed a strong burnt electronics smell coming from the K3's PA. I at that time just used it at 12 watts to Drive the KPA500 for a while as this worked fine. Today I decided to take it apart and try to determine what the issue is. After removing the  KP3A module I noticed that L23 on the main board is severely heat damaged. I wasn't expecting this, I was looking to inspect the power connector that I had fixed with the gold pins 6 months ago. Anyone have any thoughts on why L23 would fail? Before I send it to Elecraft. Thanks...
 
73 Jeff kb2m 
 
 
 
 

 


Wes Stewart
 

And the IMD will be awful.

Wes  N7WS

On Sunday, May 3, 2020, 2:59:43 PM MST, john ni0k <jasimmons@...> wrote:


Running 12 watts on data modes is bad. The low power PA won't withstand that.

-de John NI0K

Jeffrey griffin wrote on 5/3/2020 12:35 PM:
Last summer I was running more data modes (FT8) when I started having an issue with the 100 watt PA failing with a ERR 12V message. I then did the KP3A power connector replacement. This worked fine for a few months. It was working fine till I once again noticed a strong burnt electronics smell coming from the K3's PA. I at that time just used it at 12 watts to Drive the KPA500 for a while as this worked fine. Today I decided to take it apart and try to determine what the issue is. After removing the  KP3A module I noticed that L23 on the main board is severely heat damaged. I wasn't expecting this, I was looking to inspect the power connector that I had fixed with the gold pins 6 months ago. Anyone have any thoughts on why L23 would fail? Before I send it to Elecraft. Thanks...

73 Jeff kb2m 






Jeffrey griffin
 

Well I was asking anyone if they had a clue about L23, I guess not  :-)

 

I will call Elecraft tomorrow…

 

73 Jeff kb2m

 

From: Elecraft-K3@groups.io <Elecraft-K3@groups.io> On Behalf Of Wes Stewart via groups.io
Sent: Sunday, May 03, 2020 18:34
To: elecraft-k3@groups.io; Elecraft-K3@groups.io
Subject: Re: [Elecraft-K3] 100 watt PA issue

 

And the IMD will be awful.

 

Wes  N7WS

 

On Sunday, May 3, 2020, 2:59:43 PM MST, john ni0k <jasimmons@...> wrote:

 

 

Running 12 watts on data modes is bad. The low power PA won't withstand that.

-de John NI0K

Jeffrey griffin wrote on 5/3/2020 12:35 PM:

Last summer I was running more data modes (FT8) when I started having an issue with the 100 watt PA failing with a ERR 12V message. I then did the KP3A power connector replacement. This worked fine for a few months. It was working fine till I once again noticed a strong burnt electronics smell coming from the K3's PA. I at that time just used it at 12 watts to Drive the KPA500 for a while as this worked fine. Today I decided to take it apart and try to determine what the issue is. After removing the  KP3A module I noticed that L23 on the main board is severely heat damaged. I wasn't expecting this, I was looking to inspect the power connector that I had fixed with the gold pins 6 months ago. Anyone have any thoughts on why L23 would fail? Before I send it to Elecraft. Thanks...
 
73 Jeff kb2m 
 
 
 
 

 


Wes Stewart
 

According to the schematic I have, L23 is part of the 20/30 meter output LPF.  If it's been overheated I suspect a mismatched load was encountered at some time. Does your problem occur only 30 and/or 20 meters?  If so, I think you have your answer.

Wes  N7WS

On Sunday, May 3, 2020, 4:37:40 PM MST, Jeffrey griffin <kb2mjeff@...> wrote:


Well I was asking anyone if they had a clue about L23, I guess not  :-)

 

I will call Elecraft tomorrow…

 

73 Jeff kb2m

 

From: Elecraft-K3@groups.io <Elecraft-K3@groups.io> On Behalf Of Wes Stewart via groups.io
Sent: Sunday, May 03, 2020 18:34
To: elecraft-k3@groups.io; Elecraft-K3@groups.io
Subject: Re: [Elecraft-K3] 100 watt PA issue

 

And the IMD will be awful.

 

Wes  N7WS

 

On Sunday, May 3, 2020, 2:59:43 PM MST, john ni0k <jasimmons@...> wrote:

 

 

Running 12 watts on data modes is bad. The low power PA won't withstand that.

-de John NI0K

Jeffrey griffin wrote on 5/3/2020 12:35 PM:

Last summer I was running more data modes (FT8) when I started having an issue with the 100 watt PA failing with a ERR 12V message. I then did the KP3A power connector replacement. This worked fine for a few months. It was working fine till I once again noticed a strong burnt electronics smell coming from the K3's PA. I at that time just used it at 12 watts to Drive the KPA500 for a while as this worked fine. Today I decided to take it apart and try to determine what the issue is. After removing the  KP3A module I noticed that L23 on the main board is severely heat damaged. I wasn't expecting this, I was looking to inspect the power connector that I had fixed with the gold pins 6 months ago. Anyone have any thoughts on why L23 would fail? Before I send it to Elecraft. Thanks...
  
73 Jeff kb2m 
  
  
  
  

 


K9MA
 

L23 is in the 20/30m low pass filter. The only thing I can imagine could cause it to fail is a very badly mismatched load with just the wrong impedance. It's also possible, of course, that L23 was just defective.

It would not have affected operation on any other bands.

73,
Scott K9MA




On 5/3/2020 18:37, Jeffrey griffin wrote:

Well I was asking anyone if they had a clue about L23, I guess not  :-)

 

I will call Elecraft tomorrow…

 

73 Jeff kb2m

 

From: Elecraft-K3@groups.io <Elecraft-K3@groups.io> On Behalf Of Wes Stewart via groups.io
Sent: Sunday, May 03, 2020 18:34
To: elecraft-k3@groups.io; Elecraft-K3@groups.io
Subject: Re: [Elecraft-K3] 100 watt PA issue

 

And the IMD will be awful.

 

Wes  N7WS

 

On Sunday, May 3, 2020, 2:59:43 PM MST, john ni0k <jasimmons@...> wrote:

 

 

Running 12 watts on data modes is bad. The low power PA won't withstand that.

-de John NI0K

Jeffrey griffin wrote on 5/3/2020 12:35 PM:

Last summer I was running more data modes (FT8) when I started having an issue with the 100 watt PA failing with a ERR 12V message. I then did the KP3A power connector replacement. This worked fine for a few months. It was working fine till I once again noticed a strong burnt electronics smell coming from the K3's PA. I at that time just used it at 12 watts to Drive the KPA500 for a while as this worked fine. Today I decided to take it apart and try to determine what the issue is. After removing the  KP3A module I noticed that L23 on the main board is severely heat damaged. I wasn't expecting this, I was looking to inspect the power connector that I had fixed with the gold pins 6 months ago. Anyone have any thoughts on why L23 would fail? Before I send it to Elecraft. Thanks...
 
73 Jeff kb2m 
 
 
 
 

 


-- 
Scott  K9MA

k9ma@...


Bob Hammond G4DBW
 

Jeff,
The “Achilles heel “ in the K3 power stages is the 12 watt amplifier which is only conduction cooled. In normal use on SSB/ CW modes it seem to be fine all day at 12 watts out ( 8 watts out on 50MHz) Running data modes with 100% duty cycle at fully rated power 12 watts you can feel the back of the K3 chassis is uncomfortably hot after 30 minutes “running” . 

Running a K3 at 100 watts out,  the 12 watt amp is probably running 10 watts plus to drive the PA? The fan will cool the PA but don’t know how effective that is at cooling the 12 watt amp stage. 
Having said that ....have run my  K3 at 100 watts in CQ WW RTTY for long periods without problems .... 

Maybe the clever guys at Elecraft could introduce a mod to set the max power out of the 12 watt amp to only say 6 watts when running data modes? , and thus engaging the final PA stage sooner than is currently the case? 

I have a choice here on data modes running either 75 watts out of the KPA500 using a conservative 6-7 watts out of the K3 , or to set 14 watts out of the K3 to run around 175 watts out of the KPA500. This avoids the 12 watt PA being run greater than half power on 100% duty modes. 

73

Bob G4DBW


Jeffrey griffin
 

I honestly don’t think I ran the K3 at more than 7 watts, to drive the AMP there is much info on this in the archives about the 12 watt usage, I just don’t remember. Unless 7 watts data usage is a problem?  Or the failure must have been brought on by the occasional 100 watts data usage? Most of the time, about 99%, I would just use the KPA500 with the K3 at around 20 watts drive on the data modes. The KAT500 in all operating modes was always on line. I’m using a fan dipole that is pretty close to resonant on the banks in question. So maybe the KAT500 has an issue? Anyway I’m going to call Elecraft and see if I can order a replacement L23. I’m going to replace it and do some testing. Hopefully I just did do something dumb, and this fixes the problem…

 

73 Jeff kb2m

 

From: Elecraft-K3@groups.io <Elecraft-K3@groups.io> On Behalf Of robert hammond via groups.io
Sent: Monday, May 04, 2020 4:21
To: Elecraft-K3@groups.io
Subject: Re: [Elecraft-K3] 100 watt PA issue

 

Jeff,
The “Achilles heel “ in the K3 power stages is the 12 watt amplifier which is only conduction cooled. In normal use on SSB/ CW modes it seem to be fine all day at 12 watts out ( 8 watts out on 50MHz) Running data modes with 100% duty cycle at fully rated power 12 watts you can feel the back of the K3 chassis is uncomfortably hot after 30 minutes “running” . 

Running a K3 at 100 watts out,  the 12 watt amp is probably running 10 watts plus to drive the PA? The fan will cool the PA but don’t know how effective that is at cooling the 12 watt amp stage. 
Having said that ....have run my  K3 at 100 watts in CQ WW RTTY for long periods without problems .... 

Maybe the clever guys at Elecraft could introduce a mod to set the max power out of the 12 watt amp to only say 6 watts when running data modes? , and thus engaging the final PA stage sooner than is currently the case? 

I have a choice here on data modes running either 75 watts out of the KPA500 using a conservative 6-7 watts out of the K3 , or to set 14 watts out of the K3 to run around 175 watts out of the KPA500. This avoids the 12 watt PA being run greater than half power on 100% duty modes. 

73

Bob G4DBW