KPA3 output erratic


Chuck Miller
 

Still fighting a problem with my K3. When below 12 watts, every thing is fine. above 12 watts (where the KPA3 kicks in) most of the time it 0 watts, but about the same current you would expect for 100 watts. then after repeated tries, the power will come up and be stable. then the next time I press tune it is back to 0 watts. I notice if I press tune, or press the key in cw, the power is 0 for several seconds (long enough for me to send my callsign 3 or 4 times) and then the power comes back again. It will not pass TX gain calibration because the power does not rise immediately but takes several seconds. Any ideas?

73, Chuck
N0NC


mikerodgerske5gbc
 

I'm rusty on this, is this possibly gold pin syndrome?

73
Mike R

7!
Absolutely Awesome 


James Kvochick
 

Chuck;

Assuming you have already attempted to remove and reseat all of the connectors without any changes, and assuming you still can't get the KPA3 to pass the TX gain calibration, you may win a chat with Elecraft support about a PA swap.

73

Jim K8JK


Chuck Miller
 

Mike;
I had already done the gold pin replacement. The instructions said if the pins were hot and discolored to change the edge connector too. The short set of pins (the pins on the KPA3 were discolored, so I changed that edge connector. The pins on the main RF board weren't discolored, so I didn't change the longer edge connector. I thought maybe I should have, so this morning I changed the long edge connector, reassembled and checked it again. No difference.
I noticed if I set the power to about 35 watts, after a few seconds the power comes up, but oscilates a bit. I guess it's time to send Elecraft another email.

Thanks, Chuck
N0NC


Ray Maxfield
 

Hi Chuck..

I just seen your post…

Sorry if I repeat……..

It sounds like the SWR circuit is trying to Shut down the Output.

Inspect Everything on the Output of the Finals to the SO-239 Connector.

Change the Cable to your 50 Ohm Load.  

Ray WA6VAB  K3

 

From: Chuck Miller
Sent: Friday, August 7, 2020 12:00 PM
To: Elecraft-K3@groups.io
Subject: Re: [Elecraft-K3] KPA3 output erratic

 

Mike;
I had already done the gold pin replacement. The instructions said if the pins were hot and discolored to change the edge connector too. The short set of pins (the pins on the KPA3 were discolored, so I changed that edge connector. The pins on the main RF board weren't discolored, so I didn't change the longer edge connector. I thought maybe I should have, so this morning I changed the long edge connector, reassembled and checked it again. No difference.
I noticed if I set the power to about 35 watts, after a few seconds the power comes up, but oscilates a bit. I guess it's time to send Elecraft another email.

Thanks, Chuck
N0NC

 


Brian K0DTJ
 

Take a close look at the supply voltage as seen at the K3 during transmit. Significant sag will drive the power control algorithm nuts. I had a similar problem, although not as severe. Replacing the power lead with shorter, fatter wire and upping the supply voltage to 14.2 v did the trick. HTH

73,
Brian, K0DTJ

On Aug 6, 2020, at 20:16, Chuck Miller <cwmiller20@...> wrote:

Still fighting a problem with my K3. When below 12 watts, every thing is fine. above 12 watts (where the KPA3 kicks in) most of the time it 0 watts, but about the same current you would expect for 100 watts. then after repeated tries, the power will come up and be stable. then the next time I press tune it is back to 0 watts. I notice if I press tune, or press the key in cw, the power is 0 for several seconds (long enough for me to send my callsign 3 or 4 times) and then the power comes back again. It will not pass TX gain calibration because the power does not rise immediately but takes several seconds. Any ideas?

73, Chuck
N0NC


Chuck Miller
 

What amount of sag is useable? I removed the inline fuse from the power cable, and cranked the 35 amp Astron up to 14.2 volt according to the K3. It drops to 13 volts at 100w watts. The power cable is about 6 feet long as the Astron is a rack mount, and sits on the floor. The power is slow to rise mostly on 160 and 80, and to a less amount on 60 meters. 30 meters and up don't have that lagging power. Still got to check all my coax jumpers
.
73, Chuck
N0NC


Ray Maxfield
 

Have  you tested it with a Dummy Load ?

Ray  WA6VAB

 

From: Chuck Miller
Sent: Sunday, August 9, 2020 4:23 PM
To: Elecraft-K3@groups.io
Subject: Re: [Elecraft-K3] KPA3 output erratic

 

What amount of sag is useable? I removed the inline fuse from the power cable, and cranked the 35 amp Astron up to 14.2 volt according to the K3. It drops to 13 volts at 100w watts. The power cable is about 6 feet long as the Astron is a rack mount, and sits on the floor. The power is slow to rise mostly on 160 and 80, and to a less amount on 60 meters. 30 meters and up don't have that lagging power. Still got to check all my coax jumpers
.
73, Chuck
N0NC

 


mikerodgerske5gbc
 

I guess your running D.C. Straight from the astron to the k3 which is preferred. 

73
Mike R

7!
Absolutely Awesome 


Chuck Miller
 

Yep, I tested it with 2 different dummy loads, acts the same way on both. One in the MFJ tuner, and a cantenna.

Thanks, and 73
Chuck
N0NC


Brian K0DTJ
 

Hi Chuck,
I would say that 1.2v is excessive.  I started out with the 60 inch or so #12 Elecraft standard power lead and had a slow power hunting problem.  It varied by band but each time I changed the power setting or bands it go to max and then drop down and slowly come to set power.  The power calibration ran OK but didn't solve the problem.

I changed to about 3 ft of #10 stranded automotive wire in a twisted pair setup.  I set the RS-35A Astron supply to about 14.2v.  With that I get 14v at the K3 on receive and 13.3v on transmit at 100w (80m).  Measuring the voltage at the PS under load I get less than 0.1v sag in the Astron regulator.  Then ran the K3 Utility TX gain calibration _twice_ and all is OK now.

Note, in all cases the high current K3 power lead was connected directly to the Astron terminals, not though the RigRunner I use for low current 12v distribution in the shack.

Hope this helps.  Good luck.

73,
Brian, K0DTJ

On 8/9/2020 16:23, Chuck Miller wrote:
What amount of sag is useable? I removed the inline fuse from the power cable, and cranked the 35 amp Astron up to 14.2 volt according to the K3. It drops to 13 volts at 100w watts. The power cable is about 6 feet long as the Astron is a rack mount, and sits on the floor. The power is slow to rise mostly on 160 and 80, and to a less amount on 60 meters. 30 meters and up don't have that lagging power. Still got to check all my coax jumpers
.
73, Chuck
N0NC


KE1F Lou
 

I have similar issues.
Where is the internal K3 Volt meter measures the voltage?
Lou KE1F 



Sent from my Galaxy Tab® A

-------- Original message --------
From: Brian K0DTJ <huntinhmb@...>
Date: 8/10/20 12:12 AM (GMT-05:00)
To: Elecraft-K3@groups.io
Subject: Re: [Elecraft-K3] KPA3 output erratic

Hi Chuck,
I would say that 1.2v is excessive.  I started out with the 60 inch or so #12 Elecraft standard power lead and had a slow power hunting problem.  It varied by band but each time I changed the power setting or bands it go to max and then drop down and slowly come to set power.  The power calibration ran OK but didn't solve the problem.

I changed to about 3 ft of #10 stranded automotive wire in a twisted pair setup.  I set the RS-35A Astron supply to about 14.2v.  With that I get 14v at the K3 on receive and 13.3v on transmit at 100w (80m).  Measuring the voltage at the PS under load I get less than 0.1v sag in the Astron regulator.  Then ran the K3 Utility TX gain calibration _twice_ and all is OK now.

Note, in all cases the high current K3 power lead was connected directly to the Astron terminals, not though the RigRunner I use for low current 12v distribution in the shack.

Hope this helps.  Good luck.

73,
Brian, K0DTJ

On 8/9/2020 16:23, Chuck Miller wrote:
What amount of sag is useable? I removed the inline fuse from the power cable, and cranked the 35 amp Astron up to 14.2 volt according to the K3. It drops to 13 volts at 100w watts. The power cable is about 6 feet long as the Astron is a rack mount, and sits on the floor. The power is slow to rise mostly on 160 and 80, and to a less amount on 60 meters. 30 meters and up don't have that lagging power. Still got to check all my coax jumpers
.
73, Chuck
N0NC


Ed Pflueger
 

Push the DISP button and turn the VFO B knob until you see the voltage.

 

Ed.. AB4IQ

 

From: Elecraft-K3@groups.io [mailto:Elecraft-K3@groups.io] On Behalf Of KE1F Lou
Sent: Monday, August 10, 2020 8:41 AM
To: Elecraft-K3@groups.io
Subject: Re: [Elecraft-K3] KPA3 output erratic

 

I have similar issues.

Where is the internal K3 Volt meter measures the voltage?

Lou KE1F 

 

 

 

Sent from my Galaxy Tab® A

 

-------- Original message --------

From: Brian K0DTJ <huntinhmb@...>

Date: 8/10/20 12:12 AM (GMT-05:00)

Subject: Re: [Elecraft-K3] KPA3 output erratic

 

Hi Chuck,
I would say that 1.2v is excessive.  I started out with the 60 inch or so #12 Elecraft standard power lead and had a slow power hunting problem.  It varied by band but each time I changed the power setting or bands it go to max and then drop down and slowly come to set power.  The power calibration ran OK but didn't solve the problem.

I changed to about 3 ft of #10 stranded automotive wire in a twisted pair setup.  I set the RS-35A Astron supply to about 14.2v.  With that I get 14v at the K3 on receive and 13.3v on transmit at 100w (80m).  Measuring the voltage at the PS under load I get less than 0.1v sag in the Astron regulator.  Then ran the K3 Utility TX gain calibration _twice_ and all is OK now.

Note, in all cases the high current K3 power lead was connected directly to the Astron terminals, not though the RigRunner I use for low current 12v distribution in the shack.

Hope this helps.  Good luck.

73,
Brian, K0DTJ

On 8/9/2020 16:23, Chuck Miller wrote:

What amount of sag is useable? I removed the inline fuse from the power cable, and cranked the 35 amp Astron up to 14.2 volt according to the K3. It drops to 13 volts at 100w watts. The power cable is about 6 feet long as the Astron is a rack mount, and sits on the floor. The power is slow to rise mostly on 160 and 80, and to a less amount on 60 meters. 30 meters and up don't have that lagging power. Still got to check all my coax jumpers
.
73, Chuck
N0NC

 


mikerodgerske5gbc
 

Lou, I thought it was where did it read the voltage?  

Maybe not. 

Mike R

7!
Absolutely Awesome 


Bob McGraw - K4TAX
 

Power distribution strips will always add series resistance of some value. Likewise, it is strongly suggested one connect the radio power leads directly to the power supply terminals.

In-line fuses will always add series resistance and likewise for any in-line switch. Remember E = I x R? Therefore, any value of series R will cause a voltage drop, E, with the TX current of the radio.

Bob, K4TAX


James Kvochick
 

Chuck;

If you’d like, and we can get our schedules to align, I would be happy to chat with you via phone and or zoom.
For my money, I’m still betting on an issue with the final module, assuming low power TX gain calibration works.

Jim
k8jk@...


Keith_WE6R
 

What does the internal K3 show when you do a TUNE and the radio IS drawing normal current at 100 watts? (approx 18amps, depends on band etc). 
If it shows around expected power, and your external meter says zero, then the problem is somewhere between where the KAT3 or KANT3 board plugs into the RF board and your external meter. 
Check for loose center-socket on the SO-239 Ant 1 socket. Try Ant 2.

Inspect T4 on the RF board next to the KAT3 or KANT3 board, it is in the SWR/PWR sense circuit and can get burnt from DC being applied to the antenna.

But if the power drops exactly when the KPA3 kicks in, and the internal meter says 0, it is probably not the above.
I have seen one of those big blue caps, C43 & C44, right at the output of the KPA3 go bad and the radio will draw current but no RF makes it out of the amp (but they usually work or not, IE not intermittent).
Pull the KPA3 and inspect for burnt parts. Look at the big blue/black diode D10, replace if it does not look right.
You did the right thing replacing the corresponding Riser-Board connector when replacing the burnt pins. (they have always been gold-plated inside and only need to be changed if the pins get burnt).

Your slow rise of power is a puzzler. Voltage sag would result in a HI CUR message as the radio would increase gain to try to make power.
However, it could just be that you have not done a successful TX gain calibration.
**Can you get it to pass manual TX gain cal? IE set TUN PWR to nor, set to exactly 50watts, then do a TUNE for several seconds.
You should see the TXGN HP number change if successful, or get an ERR TXG if not.

You have something else beside DC voltage sag because you have issues right at 13W when the KPA3 kicks in.
But FYI;
On my Tech bench, I have about 2 feet of beefy Motorola DC cable (from their 100W trunk-mount units).
I have a digital meter remotely connected right at the Anderson cable end at the back of the radio.
I see 13.8 only drop to 13.7 at ~20 amps.
The internal K3 Display volt-meter drops from 13.8 to 13.5.  It is measured after a few things, so it is just rough accuracy.
Don't forget to set the config-menu item ADC REF. That will make the K3's internal measurements more accurate.
Keith WE6R Elecraft K3 Tech.


Chuck Miller
 

Thanks everyone for the suggestions and info. Sorry I haven't replied earlier, but we had a BIG wind come through last week (106mph straight line winds), and have not had power for a week. Just now have time and internet to answer emails.

More to come.

73, Chuck
N0NC


Chuck Miller
 

Well it's not a voltage related issue. I changed to a 3 foot power cable to a different 35 amp Astron set to 14.2 volts at the K3 Front panel. Voltage measured at Astron stable with no drop at 100 watts, voltage on the panel drops about .5 volts. I finished the mods I'm going to do for now, and it works perfect using the LPA, but once the KPA100 kicks in, the power becomes unstable. It doesn't matter if the power is set at 15, 50, or 100 watts. The power is slow to rise, especially on 160 and 80 meters, but to some extent on all bands.

"Your slow rise of power is a puzzler. Voltage sag would result in a HI CUR message as the radio would increase gain to try to make power. "
No HI CURR indication

"However, it could just be that you have not done a successful TX gain calibration.
**Can you get it to pass manual TX gain cal? IE set TUN PWR to nor, set to exactly 50watts, then do a TUNE for several seconds. You should see the TXGN HP number change if successful, or get an ERR TXG if not."

I did a TX gain cal and the TXGN HP Number changes.

Thanks for the help,
73
Chuck
N0NC


Chuck Miller
 
Edited

Well, I was grasping at straws, and remembered I had installed a used KAT3A a while back, it seemed to be working fine at first. At a loss for any thing else to try, I removed the KAT3A and the problem is gone. The funny thing is that the problem occurs whether the tuner is inline or bypassed. Now I need to trouble shoot the tuner, I'm guess, since it is a common factor, that it may be the bypass relay.

I've ordered the replacement relay from Elecraft, so I will see if that helps.

Thanks for all the help guys.
73, Chuck
N0NC