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K3 #00626 - help with KPA3 Rev B schematic

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E Turk

K3 #00626 - help with KPA3 Rev B schematic

Hello All,

I have recently acquired an early K3 which needs tidying and checking over. So far all appears to be OK except for the KPA3 which gives no RF output but the rig draws 14 Amps regardless of the power setting. The LPA is working fine with up to 12 W RF out and a max current draw of 4 W.

Visual checking of the KPA3 board reveals nothing amiss but also shows considerable component differences compared to the only schematic I could find on the Elecraft website - the Rev C version.

If any of you early adopters have a .PDF schematic for the KPA3 Rev B, I would be most grateful for an electronic copy.

73, Ted G7BQM (with quite a lot of Elecraft stuff!)

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E Turk

Re: K3 #00626 - help with KPA3 Rev B schematic

Many thanks for your reply Peter.

The Rev C schematics are the ones on the current Elecraft website, which I have. I was suspicious of the pins which are the originals, but they look OK and Deoxit has not cured the problem. Yesterday my order of some ribbon cables arrived, and I was able to run the KPA3 outside the chassis upside down. On demanding more than 12 W power there was a rapid smell of hot electronics but no smoke. The 2 x 51 ohm 3 W grey resistors were hot enough to cause a minor burn! I have still to determine where the rest of the power is going - the transistors?

If you have any details of the bias setting method, that would be really helpful. I have not been able to find any information on this on the internet.

Thanks for the good luck - I need it.

73, Ted G7BQM

> On 23 Feb 2019, at 12:29, Peter Torry <[hidden email]> wrote:
>
> Hi Ted,
>
> I have the schematics from 2008 but they were rev C if they are of use to you.
>
> There was an issue with the KPA100 which was cured by fitting new gold plated connectors, free from Elecraft but just try removing the PA and refitting it to remove any issues with oxidation of contacts. De-Oxit is good for this as well. Could be worth checking the bias setting.
>
> Good luck with the repair.
>
> 73
>
> Peter
>
> G3SMT
>
>
> On 23/02/2019 12:14, Ted G7BQM wrote:
>> Hello All,
>>
>> I have recently acquired an early K3 which needs tidying and checking over. So far all appears to be OK except for the KPA3 which gives no RF output but the rig draws 14 Amps regardless of the power setting. The LPA is working fine with up to 12 W RF out and a max current draw of 4 W.
>>
>> Visual checking of the KPA3 board reveals nothing amiss but also shows considerable component differences compared to the only schematic I could find on the Elecraft website - the Rev C version.
>>
>> If any of you early adopters have a .PDF schematic for the KPA3 Rev B, I would be most grateful for an electronic copy.
>>
>> 73, Ted G7BQM (with quite a lot of Elecraft stuff!)
>>
>>
>>
>>
>> ______________________________________________________________
>> 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
>

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E Turk

Re: K3 #00626 - help with KPA3 Rev B schematic

In reply to this post by E Turk

Thanks to those who contacted me. Nobody seems to have a Rev B Schematic!

The possibility of an exchange unit has not materialised so as the KPA3 is still mine, I decided a bit of disassembly was in order before taking it to be serviced.

Findings upon removal for testing:

C43 and C44 passed testing with a Peak LCR45 - refitted

R27 OK - refitted

D7,8 & 9 OK with Peak DCA75 - replaced since I could get these and they are very cheap

D10 Pin Diode tested as ‘no component’ with Peak DCA75 and multimeter shows open circuit

The MA4P4006B-402 600V Pin Diode does not appear to be available for sale in the UK, but I am checking with the service centre.

Conclusions:

One fault found, need to repair that before further testing. Since I do not know the history of the unit, which was a Silent Key sale, there is no information about the likely cause of this failure.

Many thanks once again - I will post the final outcome on the reflector, once all is working again.

73, Ted G7BQM

> On 23 Feb 2019, at 12:14, Ted G7BQM <[hidden email]> wrote:
>
> Hello All,
>
> I have recently acquired an early K3 which needs tidying and checking over. So far all appears to be OK except for the KPA3 which gives no RF output but the rig draws 14 Amps regardless of the power setting. The LPA is working fine with up to 12 W RF out and a max current draw of 4 A.
>
> Visual checking of the KPA3 board reveals nothing amiss but also shows considerable component differences compared to the only schematic I could find on the Elecraft website - the Rev C version.
>
> If any of you early adopters have a .PDF schematic for the KPA3 Rev B, I would be most grateful for an electronic copy.
>
> 73, Ted G7BQM (with quite a lot of Elecraft stuff!)
>
>
>
>
> ______________________________________________________________
> 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
>