Topics

K3s no power on TX

Brian
 

Hi All

Hope you are keeping well.

I have a K3s that has no power output that appears to have failed while not in use.

In tune there is no detected output on a Bird wattmeter with a 50 watt slug. When connected to a KX3 via a 30 dB attenuator the KX3 reports an S9 for an instant when the K3s tune is pressed, quickly dropping to S5.

There are no apparent problems on RX. The KPA3 has been set to bypass for test purposes. 

The TX filter is set to 2.8 kHz for SSB and CW. Testing is mostly being done in CW.

It would seem that the problem should be in the path between the SWR bridge and ANT 1 connector ( no ATU in K3s), however, as receiver works as well as another K3s on an AM broadcast station on 40M this seems unlikely.

I suspect the 10W PA driver or the switching diodes around it.

Has anyone seen this problem that can give advice before I start taking the K3s further apart?

Thanks

Brian KF6C.

Alan Baker
 

Hi Brian.

Have you checked that the rig is not in TEST mode?

RH Mode button, press and hold.

It's an easy one to miss when all else appears OK, but you get no RF output.

73,

Alan. G4GNX


------ Original Message ------
From: "Brian" <brian@...>
Sent: 18/05/2020 23:18:02
Subject: [Elecraft-K3] K3s no power on TX

Hi All

Hope you are keeping well.

I have a K3s that has no power output that appears to have failed while not in use.

In tune there is no detected output on a Bird wattmeter with a 50 watt slug. When connected to a KX3 via a 30 dB attenuator the KX3 reports an S9 for an instant when the K3s tune is pressed, quickly dropping to S5.

There are no apparent problems on RX. The KPA3 has been set to bypass for test purposes. 

The TX filter is set to 2.8 kHz for SSB and CW. Testing is mostly being done in CW.

It would seem that the problem should be in the path between the SWR bridge and ANT 1 connector ( no ATU in K3s), however, as receiver works as well as another K3s on an AM broadcast station on 40M this seems unlikely.

I suspect the 10W PA driver or the switching diodes around it.

Has anyone seen this problem that can give advice before I start taking the K3s further apart?

Thanks

Brian KF6C.

Everett N4CY
 

You also need to check to make sure you have ANT 1 selected, check to see what ANT is selected on the display. 

Everett N4CY 

On May 18, 2020, at 5:18 PM, Brian <brian@...> wrote:

Hi All

Hope you are keeping well.

I have a K3s that has no power output that appears to have failed while not in use.

In tune there is no detected output on a Bird wattmeter with a 50 watt slug. When connected to a KX3 via a 30 dB attenuator the KX3 reports an S9 for an instant when the K3s tune is pressed, quickly dropping to S5.

There are no apparent problems on RX. The KPA3 has been set to bypass for test purposes. 

The TX filter is set to 2.8 kHz for SSB and CW. Testing is mostly being done in CW.

It would seem that the problem should be in the path between the SWR bridge and ANT 1 connector ( no ATU in K3s), however, as receiver works as well as another K3s on an AM broadcast station on 40M this seems unlikely.

I suspect the 10W PA driver or the switching diodes around it.

Has anyone seen this problem that can give advice before I start taking the K3s further apart?

Thanks

Brian KF6C.

Brian
 

It is not in Test Mode, it is certainly possible it is somthing like this I have missed.

It displays ANT 1 and without the ATU I dont think it will go to ANT2.

Brian

Mel Marcus
 

I had something similar happen to me. it ended up that it was dirty contact on the XREF. if the PA does not get timing then there is not transmit. the suggestion from Elecraft was to clean the contacts both on the pin side and on the cable side. in fact they said the next step is to test those cables. if the cables are bad replace them

Mel
NE9A

-------- Original Message --------
Subject: [Elecraft-K3] K3s no power on TX
From: "Brian" <brian@...>
Date: Mon, May 18, 2020 5:18 pm
To: Elecraft-K3@groups.io

Hi All

Hope you are keeping well.

I have a K3s that has no power output that appears to have failed while not in use.

In tune there is no detected output on a Bird wattmeter with a 50 watt slug. When connected to a KX3 via a 30 dB attenuator the KX3 reports an S9 for an instant when the K3s tune is pressed, quickly dropping to S5.

There are no apparent problems on RX. The KPA3 has been set to bypass for test purposes. 

The TX filter is set to 2.8 kHz for SSB and CW. Testing is mostly being done in CW.

It would seem that the problem should be in the path between the SWR bridge and ANT 1 connector ( no ATU in K3s), however, as receiver works as well as another K3s on an AM broadcast station on 40M this seems unlikely.

I suspect the 10W PA driver or the switching diodes around it.

Has anyone seen this problem that can give advice before I start taking the K3s further apart?

Thanks

Brian KF6C.

Bob Evans
 

Brian,

 

If this rig has been sitting unused for a while, I’ll bet it is simply a connection problem between board/components.  If you have the KAT3, try reseating the coax cables connected to it…both ends.   Same with the KSYN3A and KRX3 (if you have it).  Another batch of connections that might be the culprit can be reseated by removing the front face and carefully replugging it.  I believe the K3S may have gold pins there but it is worth a shot.  Lastly, you might reseat the KLPA3A board (the little square board inserted in the main board accessible from the bottom I think).  I had this problem once on one of my three K3s and it was scary until I fixed it and it never happened again on any of them.  My money is on the KLPA3 and/or the KSYN3 being the culprit.

 

Hopefully, someone else will give you a better answer since I’m basically an appliance operator(engineer wannabe) but these would be where I would look.  Probably in reverse order as I listed them now that I’m thinking about this a bit.  😉

 

Good luck,

 

Bob K5WA

Waiting on a pair of K4HDs

Bob Novas
 

Brian - if you’re using CW to test transmit, make sure you’ve got VOX and not PTT selected.  Bob

 

From: Elecraft-K3@groups.io [mailto:Elecraft-K3@groups.io] On Behalf Of Brian
Sent: Monday, May 18, 2020 8:41 PM
To: Elecraft-K3@groups.io
Subject: Re: [Elecraft-K3] K3s no power on TX

 

It is not in Test Mode, it is certainly possible it is somthing like this I have missed.

It displays ANT 1 and without the ATU I dont think it will go to ANT2.

Brian

K9MA
 

Brian,

Do you have an oscilloscope and some experience using it? Unlike a lot of modern radios, the K3 is really pretty easy to work on. With an oscilloscope, you should be able to look at the signal train and determine where the fault is.

Meanwhile, as others have suggested, clean the connectors, as that's the most likely thing to have failed while sitting unused.

73,
Scott K9MA

On 5/19/2020 09:19, Bob Evans wrote:

Brian,

 

If this rig has been sitting unused for a while, I’ll bet it is simply a connection problem between board/components.  If you have the KAT3, try reseating the coax cables connected to it…both ends.   Same with the KSYN3A and KRX3 (if you have it).  Another batch of connections that might be the culprit can be reseated by removing the front face and carefully replugging it.  I believe the K3S may have gold pins there but it is worth a shot.  Lastly, you might reseat the KLPA3A board (the little square board inserted in the main board accessible from the bottom I think).  I had this problem once on one of my three K3s and it was scary until I fixed it and it never happened again on any of them.  My money is on the KLPA3 and/or the KSYN3 being the culprit.

 

Hopefully, someone else will give you a better answer since I’m basically an appliance operator(engineer wannabe) but these would be where I would look.  Probably in reverse order as I listed them now that I’m thinking about this a bit.  😉

 

Good luck,

 

Bob K5WA

Waiting on a pair of K4HDs


-- 
Scott  K9MA

k9ma@...

Keith_WE6R
 

See if it will make MW power with the KXV3 in test mode (if equipped). That will tell you if the problem is before or after.
Does the RX work fine?
Keith WE6R, Elecraft K3 Tech.

Bob Wilson, N6TV
 

Long shot:  

In normal mode (not TEST mode), no power out can happen if CONFIG:TX INH is set to Lo=Inh instead of to the default: OFF.  To check that CONFIG menu setting, first set CONFIG:TECH MD to ON.  

But if the TX LED lights up when you're in CW mode, and you can still hear CW sidetone, then it's not the Inhibit line, but something else.  Also, when transmissions are inhibited, the TX symbol will blink on the LCD display, like it does when in TEST mode.

73,
Bob, N6TV


On Mon, May 18, 2020 at 3:18 PM Brian <brian@...> wrote:
Hi All

Hope you are keeping well.

I have a K3s that has no power output that appears to have failed while not in use.

In tune there is no detected output on a Bird wattmeter with a 50 watt slug. When connected to a KX3 via a 30 dB attenuator the KX3 reports an S9 for an instant when the K3s tune is pressed, quickly dropping to S5.

There are no apparent problems on RX. The KPA3 has been set to bypass for test purposes. 

The TX filter is set to 2.8 kHz for SSB and CW. Testing is mostly being done in CW.

It would seem that the problem should be in the path between the SWR bridge and ANT 1 connector ( no ATU in K3s), however, as receiver works as well as another K3s on an AM broadcast station on 40M this seems unlikely.

I suspect the 10W PA driver or the switching diodes around it.

Has anyone seen this problem that can give advice before I start taking the K3s further apart?

Thanks

Brian KF6C.

Brian
 

First let me thank you all for your suggestions,  all were very much appreciated.

These units have been removed from the radio:
K144XV
KRX3A,
KPA3A,
KBPF3.

I have also removed the KAT board and made a direct connection.

There is low power output in the KXV3 test mode.

The KLPA3A is Rev B. Looking at the schematic, taken from the web,  which is also for Rev B there are differences between what the schematic shows and what is in the radio. There are 2 relays KL2 and KL3 on the schematic that are not on the board in the radio.

With tune on there is 1 volt p to p input and 2.4 volt p to p output on the KLPA3A.There are no change in these readings on power control adjustment. I have not yet understood how power control adjustment is implemented.

4 dBm would seem adequate drive for the  KLPA3A.

What is the part number of U4 is not given on the schematic?

I have not seen anything obviously wrong on the KLPA3A but the voltage gains throughout seem low.

73 Brian KF6C.

K9MA
 

Brian,

I suspect Elecraft decided they didn't need KL2 and KL3, which just switch in attenuation.

I'm pretty sure the input to the KLPA3A should change with power setting, as there's nothing downstream which could control power. Maximum input to the KLPA3A should be around 1 V p-p, but output should be around 63 V P-P.

I don't know why you're seeing constant input to the KLPA3A, but if you're only seeing 4 V P-P at the output, it definitely has a problem. Look at the outputs of U4, U2, and U3. Assuming U4 is the same as U2 and U3, each should have about 20 dB of gain.

Hope that helps. Have you tried contacting Elecraft tech support?

73,
Scott K9MA

On 5/20/2020 10:47, Brian wrote:
First let me thank you all for your suggestions,  all were very much appreciated.

These units have been removed from the radio:
K144XV
KRX3A,
KPA3A,
KBPF3.

I have also removed the KAT board and made a direct connection.

There is low power output in the KXV3 test mode.

The KLPA3A is Rev B. Looking at the schematic, taken from the web,  which is also for Rev B there are differences between what the schematic shows and what is in the radio. There are 2 relays KL2 and KL3 on the schematic that are not on the board in the radio.

With tune on there is 1 volt p to p input and 2.4 volt p to p output on the KLPA3A.There are no change in these readings on power control adjustment. I have not yet understood how power control adjustment is implemented.

4 dBm would seem adequate drive for the  KLPA3A.

What is the part number of U4 is not given on the schematic?

I have not seen anything obviously wrong on the KLPA3A but the voltage gains throughout seem low.

73 Brian KF6C.


-- 
Scott  K9MA

k9ma@...

Brian
 

I sent this message to Technical Support a few days ago, not to sure it got through.

Sn 10174
This K3S failed on transmit. There were no known issues when it last worked in CA, it did not work after being transported to NY.

Even given the above there appears to be a fault with the KLPA3A.

The follow measurements were made on KLPA3A at 7.068 MHz.

Output of U4,  4V p to p.

Input T1, 3.1 p to p.

Input U3, 1.5 p to p.

Input U3, 1.5 p to p.

I have oscilloscope pictures of the input and outputs of Q4 and 5.

There are differences between the schematic given on the web and the circuit in the radio, is it possible to get an accurate schematic? What is the manufacturers part number for  U4?

The problem appears to be in the U2/U3 stage but all DC voltages appear to be within what I would expect, except for the drain voltages on Q4 and 5. I therefore suspect these devices have failed and are loading the outputs of U2 and 3.

I would apricate your input on the likelihood of this diagnosis being correct. If you think it is correct can you, please give me the cost of two RD15HVF1.

Ray Maxfield
 

Brian….. The First thing I would Do is to Re-seat ALL of the Cards.

ANY Card that can be RE-Connected or Reseated I would do.

And Inspect the Traces and Contacts on each connector …

Ray WA6VAB   K3 Owner.

 

 

 

Sent from Mail for Windows 10

 

From: Brian
Sent: Wednesday, May 27, 2020 2:17 PM
To: Elecraft-K3@groups.io
Subject: Re: [Elecraft-K3] K3s no power on TX

 

I sent this message to Technical Support a few days ago, not to sure it got through.

Sn 10174
This K3S failed on transmit. There were no known issues when it last worked in CA, it did not work after being transported to NY.

Even given the above there appears to be a fault with the KLPA3A.

The follow measurements were made on KLPA3A at 7.068 MHz.

Output of U4,  4V p to p.

Input T1, 3.1 p to p.

Input U3, 1.5 p to p.

Input U3, 1.5 p to p.

I have oscilloscope pictures of the input and outputs of Q4 and 5.

There are differences between the schematic given on the web and the circuit in the radio, is it possible to get an accurate schematic? What is the manufacturers part number for  U4?

The problem appears to be in the U2/U3 stage but all DC voltages appear to be within what I would expect, except for the drain voltages on Q4 and 5. I therefore suspect these devices have failed and are loading the outputs of U2 and 3.

I would apricate your input on the likelihood of this diagnosis being correct. If you think it is correct can you, please give me the cost of two RD15HVF1.

 

Bob Wilson, N6TV
 

The most common reason that a K3 stops working after being transported is that the little interface card that connects the rear of the Sub Receiver box to the motherboard becomes unseated from the pins.

Did you check that?  It's easier to see if you unscrew the mounting screws and pull the SubRx up (no need to disconnect cables).

73,
Bob, N6TV

On Wed, May 27, 2020 at 2:17 PM Brian <brian@...> wrote:
I sent this message to Technical Support a few days ago, not to sure it got through.

Sn 10174
This K3S failed on transmit. There were no known issues when it last worked in CA, it did not work after being transported to NY.

Even given the above there appears to be a fault with the KLPA3A.

The follow measurements were made on KLPA3A at 7.068 MHz.

Output of U4,  4V p to p.

Input T1, 3.1 p to p.

Input U3, 1.5 p to p.

Input U3, 1.5 p to p.

I have oscilloscope pictures of the input and outputs of Q4 and 5.

There are differences between the schematic given on the web and the circuit in the radio, is it possible to get an accurate schematic? What is the manufacturers part number for  U4?

The problem appears to be in the U2/U3 stage but all DC voltages appear to be within what I would expect, except for the drain voltages on Q4 and 5. I therefore suspect these devices have failed and are loading the outputs of U2 and 3.

I would apricate your input on the likelihood of this diagnosis being correct. If you think it is correct can you, please give me the cost of two RD15HVF1.

Brian
 

Hi Bob

 

I have the Sub Receiver removed. The interface card has been removed and replaced a few times in my testing.

 

I have reseated all the connections within the radio.

 

Although I first noticed the problem after it was moved from CA to NY, after some serios checks I no longer believe the problem occurred in transport.

 

I am 90 % sure the RD15HVF1s have failed. As this is now  a spare K3S I have time to play fixing it, I am in no hurry to start unsoldering parts in my diagnostics.

 

I have a few ways to go, get some conformation from Elecraft that my diagnostics is reasonable correct, run simulations  of the circuit, compare to my working K3S or just change the parts, I am trying the first for a start.

 

This radio was assembled by a kid who built a K2/100 at age 6 and assembled both my K3S, with little supervision, so I have not delved into these radio much in the past.

 

73 Brian KF6C.

Ray Maxfield
 

Hi Brian

I did the Finger Heat Test on My K3 when it died.

Reach under the radio where the 3 Power fets are mounted

And Feel the Screws that Mount the Fets.

Key the Transmitter ( maybe AM Mode) you should feel the Screw get Warm

If no Heat, most likely Bad.

You can get The Fets from Elecraft ,ebay   internet.

Ray   WA6VAB   K3.   Rocklin CA.

 

From: Brian
Sent: Thursday, May 28, 2020 4:15 AM
To: Elecraft-K3@groups.io
Subject: Re: [Elecraft-K3] K3s no power on TX

 

Hi Bob

 

I have the Sub Receiver removed. The interface card has been removed and replaced a few times in my testing.

 

I have reseated all the connections within the radio.

 

Although I first noticed the problem after it was moved from CA to NY, after some serios checks I no longer believe the problem occurred in transport.

 

I am 90 % sure the RD15HVF1s have failed. As this is now  a spare K3S I have time to play fixing it, I am in no hurry to start unsoldering parts in my diagnostics.

 

I have a few ways to go, get some conformation from Elecraft that my diagnostics is reasonable correct, run simulations  of the circuit, compare to my working K3S or just change the parts, I am trying the first for a start.

 

This radio was assembled by a kid who built a K2/100 at age 6 and assembled both my K3S, with little supervision, so I have not delved into these radio much in the past.

 

73 Brian KF6C.

 

Richard Williams
 

I would venture to say that no power out (especially in the 1 - 12 watt range indicated the failure of both MOSFETs (about half power indicates failure of one of them).   I have had that happen twice now; and it is not a difficult task to replace the two RD15HVF1s.

I purchased mine from RF Parts; they are $4.95 each, and shipping is $12.15;  SO, I purchased six of them (now have 4 spares).

Easy to remove the KLPA3A  board.  Remove the top cover, and bottom read cover. Then remove the fan(s) and the KPA3A 100W Amp board (three screws - two in back and one on the right side when looking from the back).  This gives you access to the KLPA3A board.  You can now pop out the KLPA3A board, and replace the two MOSFETs.

Once done put the board back in secure the bottom cover; leave the KPA3A amplifier out (you need access to the 2 pots on the KLPA board to set the bias).

Fire up the K3S with an amp meter in the power line; if you do not have one, you can use the meter in the K3S.  To do that, tap the DISP button, then use the VFO B know to change the display to Amps.  Set the radio to SSB mode, power knob all the way down, and press the tune button (puts the radio in transmit mode).

With the two pots on the KLPA3A board full CCW, adjust either one for a 200 MA increase in current. Then adjust the other pot for another 200 MA increase.  You are now done, power down the radio, re-install the power amp, fan board on back of the power amp, and then the top cover.

When I adjusted the pots, I had a meter in series with the power lead from the power supply, and watched the meter on the front of the K3S.  The readings were surprisingly close, so either is more than satisfactory to use.

One other note, when you remove the back bottom cover, make sure there are grey (mine are) thermal pads on the RD15HVF1s; you need to transfer those over to the new ones.

Dick, K8ZTT



Flying is the second greatest thrill known to man.
What is first, you ask? Landing, of course.







On Thursday, May 28, 2020, 07:52:27 AM MDT, Ray Maxfield <wa6vab@...> wrote:


Hi Brian

I did the Finger Heat Test on My K3 when it died.

Reach under the radio where the 3 Power fets are mounted

And Feel the Screws that Mount the Fets.

Key the Transmitter ( maybe AM Mode) you should feel the Screw get Warm

If no Heat, most likely Bad.

You can get The Fets from Elecraft ,ebay   internet.

Ray   WA6VAB   K3.   Rocklin CA.

 

From: Brian
Sent: Thursday, May 28, 2020 4:15 AM
To: Elecraft-K3@groups.io
Subject: Re: [Elecraft-K3] K3s no power on TX

 

Hi Bob

 

I have the Sub Receiver removed. The interface card has been removed and replaced a few times in my testing.

 

I have reseated all the connections within the radio.

 

Although I first noticed the problem after it was moved from CA to NY, after some serios checks I no longer believe the problem occurred in transport.

 

I am 90 % sure the RD15HVF1s have failed. As this is now  a spare K3S I have time to play fixing it, I am in no hurry to start unsoldering parts in my diagnostics.

 

I have a few ways to go, get some conformation from Elecraft that my diagnostics is reasonable correct, run simulations  of the circuit, compare to my working K3S or just change the parts, I am trying the first for a start.

 

This radio was assembled by a kid who built a K2/100 at age 6 and assembled both my K3S, with little supervision, so I have not delved into these radio much in the past.

 

73 Brian KF6C.

 

Brian
 

Thanks for the info Richard. I had already  purchased the MOSFETS from RF Parts.

 

I had not thought of looking at the temp rise on the devices but had noted that their drains were at 12 volts so little current is being drawn. The radio is running on a supply with a current meter so that is no problem. I have already taken out the KLPA3A board and put it back in so no issues there. I think I will remove the RD15HCVF1s and look at the outputs of the SGA 7489s for future reference, before I replace the MOSFETS.

 

I was pretty sure the MOSFETS had failed but not so sure what their typical failed state is. Thanks for giving your experience.

 

73 Brian KF6C.

mikerodgerske5gbc
 

Those things are a definite weakness as they are a common failure. I think my failed twice with something weird on 15 meters with a amp I was using. 

With the k3/10 anyway there was and maybe still no swr protection for the lpa board. 

73
Mike R

7!
Absolutely Awesome 

On May 28, 2020, at 6:44 PM, Brian <brian@...> wrote:

Thanks for the info Richard. I had already  purchased the MOSFETS from RF Parts.

 

I had not thought of looking at the temp rise on the devices but had noted that their drains were at 12 volts so little current is being drawn. The radio is running on a supply with a current meter so that is no problem. I have already taken out the KLPA3A board and put it back in so no issues there. I think I will remove the RD15HCVF1s and look at the outputs of the SGA 7489s for future reference, before I replace the MOSFETS.

 

I was pretty sure the MOSFETS had failed but not so sure what their typical failed state is. Thanks for giving your experience.

 

73 Brian KF6C.