KPA3 gives no output
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Steef PA2A <pa2a@...>
Hi,
after reassembling the K3 the KPA3 gives no output. The 12 Watts low power works fine and cranking up the power the relay clicks but 0 Watts output. The TUNE lets the KPA draw excessive current, and tuning 13 or 110 Watts makes no difference. On 12 and 10 meters the 25+ Amps currents cause the HI CUR warning and the power goes to 5 Watts.
What might be the problem? There is no 12 Volt error, connectors are gold types.
73s Steve PA2A
#1184 |
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Ron K5MM
Steve,
I believe I had the same issue. Elecraft provided this advise:
For me it was R5 which was removed and replaced with E500118, the 100ohm 3Watt resister in the picture below: On Nov 5, 2022, at 6:16 AM, Steef PA2A via groups.io <pa2a@...> wrote:
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Ray Maxfield
Hi Steef I am not sure what you have looked at before, but it sounds like the Final output stage is defective. I would Check the 2 Fets in the output…… Q2 and Q3 for Shorts. Ray WA6VAB K3
From: Steef PA2A
Sent: Saturday, November 5, 2022 4:16 AM To: Elecraft-K3@groups.io Subject: [Elecraft-K3] KPA3 gives no output
Hi,
after reassembling the K3 the KPA3 gives no output. The 12 Watts low power works fine and cranking up the power the relay clicks but 0 Watts output. The TUNE lets the KPA draw excessive current, and tuning 13 or 110 Watts makes no difference. On 12 and 10 meters the 25+ Amps currents cause the HI CUR warning and the power goes to 5 Watts. What might be the problem? There is no 12 Volt error, connectors are gold types.
73s Steve PA2A #1184
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Steef PA2A <pa2a@...>
Hi Ray,
the KPA3 board is an old one, rev. B from 2007 and there are 2SC2782 transistors on it. The KPA3A boards in the K3S have the RD100HHF1 power fets on board.
As reception is weaker while the KPA3 is turned on at power levels from 12 Watts, I suspect a bad component in the RX/TX circuitry on the KPA3 board. All possible bad solder joints oner the SMD components have been examined and soldered again.
73s Steve PA2A
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Mike - K8CN
Steef,
Check diodes D7 and D10 on the KPA3 board.
These PIN diodes route RF through the KPA3
when TX power levels above 11 watts are commanded.
Diodes D8 and D9 may be OK since this path
is active when only the low power TX module (LPA)
is used (i.e. TX power less than 11 watts commanded)
and in RX mode.
Poor RX sensitivity when TX power is set above
11 watts is again indicative of either diode D7
or D10 having failed and causing signal suck-out
on RX.
The high current warning when KPA3 is engaged
in TX or TUNE mode likely indicates failure (collector-base short) of
either or both of the KPA3 final transistors.
Was the KPA3 working properly before you
removed it?
73,
Mike, K8CN
From: Elecraft-K3@groups.io <Elecraft-K3@groups.io> on behalf of Steef PA2A <pa2a@...>
Sent: Saturday, November 5, 2022 5:08 PM To: Elecraft-K3@groups.io <Elecraft-K3@groups.io>; Ray Maxfield <wa6vab@...> Subject: Re: [Elecraft-K3] KPA3 gives no output
CAUTION: This email originated from outside of the University System. Do not click links or open attachments unless you recognize the sender and know the content is safe.
Hi Ray,
the KPA3 board is an old one, rev. B from 2007 and there are 2SC2782 transistors on it. The KPA3A boards in the K3S have the RD100HHF1 power fets on board.
As reception is weaker while the KPA3 is turned on at power levels from 12 Watts, I suspect a bad component in the RX/TX circuitry on the KPA3 board. All possible bad solder joints oner the SMD components have been examined and
soldered again.
73s Steve PA2A
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Steef PA2A <pa2a@...>
Mike,
I will replace diodes D7 and D10. It is difficult to do measurements in the KPA3 when mounted in the K3. If replacing them does not solve the problem I will try to check the final transistors by removing some components and make it possible to do the checking.
73s Steve PA2A
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Look real closely at the legs of the 4 big red coils.
Since this happened when you were working on it, it is easy to set it down on them or bump them and crack one of the legs. (ask me how!). Since they are siliconed down, you have to look REAL close and gently flex them both ways looking for a small crack. One of them being cracked will also take out the Receive (above 12W). Another possible is the relay on the KPAIO3 riser board. Click repeatedly while in receive to see if it is intermittent. Another thing,.. Is it drawing full current on all bands when set above 12W? If so, it is probably making power, it is just not getting out for some reason, the above relay maybe, or also I have seen one of those big blue caps open up, C43 & C44. Keith WE6R Elecraft K3/K4 Tech |
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Steef PA2A <pa2a@...>
Hi Keith,
thanks for all useful info! I will measure all components and maybe one of the red coils has been broken. There have been real forces on the KPA3 when putting it back after the modification of R4 and R5.
It is so difficult to measure things when the KPA3 is in place. Maybe I will create some extenders by using old IDE harddisk cables.
The high currents are on all bands when tuning above 12 Watts. Power settings of 13 and 110 Watts give the same results. On 12 en 10 meters the current goes towards 30 Amps. The 20 Amp fuse does not trip. I also think that there is power being made. I will connect a probe or so.
73s Steve PA2A
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Geert Jan de Groot
Sorry for asking, I just didn't see this exact situation mentioned in this thread: do you get the excessive current message also when set the radio above 12W and just TX (no RF signal), or do you need to TUNE (RF signal) to make it happen?
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Steef PA2A <pa2a@...>
Hi Geert Jan,
als ik alleen op TX druk lopen de grote stromen niet, alleen inderdaad in de TUNE stand. Er wordt dan geprobeerd om vermogen te maken dat niet aankomt bij de detectie. Ik ga een verloopprintje maken zodat ik wat kan meten in de KPA3. En misschien zijn het toch C43 of C44. Keith gaf ook aan dat een breuk in een van de spoelen zou kunnen zitten.
Ik ga kijken of ik wat componenten kan verwijderen om te zien waar de RX weglekt. Ik heb er alleen niet zoveel tijd voor.
Wordt vervolgd hi!
73s Steef PA2A
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Geert Jan de Groot
(for people who missed Steef's comments: In TX mode, no big currents are flowing, only in TUNE, so I have hope for his KPA3 transistors)
Keith, while looking at Steef's fault description, the K3 schematics, your comments and the various symptoms, would it be possible to elaborate what "MENU:KPA3 PAIO BYP" does? I am trying to decide whether this would be a defect in the KPAIO3 interface board (issue around KPAIO3:K1) or whether the diode switching on page 2 of the KPA3 schematics is the more likely cause. and how to diagnose it. Also, without RF being detected, the K3 will go for full RF drive, and I worry if the RF power just "disappears". Any way we can reduce the RF drive so that the KPA3 finals stand a chance of surviving while we try to find where the RF power goes? Reduced K3 DC input voltage? |
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Steef PA2A <pa2a@...>
Hi all,
the KPA3 works fine again. One of the red coils was broken at the base. Thanks for all advices! 73s Steve PA2A |
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Mike - K8CN
I'm glad you found the source of the 'no output'
behavior of your K3, Steef! Keith, WE6R has
seen it all and he flagged all the possible sources
of the loss of TX output you experienced. Those
red coils (toroids, iron powder) are the RF chokes
in the DC bias lines to the PIN diode T/R and
KPA3 bypass circuits, so loss of that DC bias
would prevent the affected PIN diode from
changing state.
73,
Mike, K8CN
From: Elecraft-K3@groups.io <Elecraft-K3@groups.io> on behalf of Steef PA2A <pa2a@...>
Sent: Thursday, November 10, 2022 11:47 AM To: Elecraft-K3@groups.io <Elecraft-K3@groups.io> Subject: Re: [Elecraft-K3] KPA3 gives no output
CAUTION: This email originated from outside of the University System. Do not click links or open attachments unless you recognize the sender and know the content is safe.
Hi all,
the KPA3 works fine again. One of the red coils was broken at the base. Thanks for all advices! 73s Steve PA2A |
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