[Elecraft] Issues with KPA100 (K2/10 is 100% OK)

[dl9hda at dl9hda.de]

Hi, the KPA100 is alive. I startet to desolder D16 and D17 but D16 
broke. D17 was OK. I soldered two new 1N5711 and now after some minor 
adjustments the KPA100 is back!


best regards
Holger. DL9HDA





Am 2014-05-05 22:20, schrieb Don Wilhelm:
> Holger,
> 
> That indicates that D11 is shorted.  I would replace D11, D12 and D14
> and remeasure.
> Do not substitute - use only 1N4007s.  While those are normally power
> diodes, they work well for switching purposes too, and that is not
> true of most other diode types.
> 
> 73,
> Don W3FPR
> 
> On 5/5/2014 4:05 PM, dl9hda at dl9hda.de wrote:
>> Dear Don,
>> 
>> thank you very much for your answer. I checked it with an wattmeter 
>> and a dummy load. Nothing.
>> 
>> But I checked the voltages at the diodes especially D11, D12, D13 and 
>> D14 in receive-mode:
>> 
>> D12 and D14 have the right voltages at the anodes and cathodes when I 
>> switch from low-power to high-power and vice-versa.
>> 
>> But the voltages at D11 and D13 are wrong. The voltages at the anodes 
>> and cathodes are always 13,8V. There are no voltages about ~140V. At 
>> D12 and D14 I can measure this high voltages at the cathodes.
>> 
>> 
>> 
>> best regards
>> Holger, DL9HDA
>> 
>> 
>> 
>> 
>> Am 2014-05-05 21:55, schrieb Don Wilhelm:
>>> Holger,
>>> 
>>> Those resistance values indicate that D16 and D17 in the KPA100 are
>>> faulty.  The resistance in the forward direction should normally be
>>> much lower.  You can check to see if your ohmmeter is reading 
>>> properly
>>> by measuring a new or known good small signal diode.
>>> 
>>> I believe if you check the power output with an external wattmeter 
>>> and
>>> connected to a dummy load, you will find a higher than normal power
>>> even though the K2 display and LED Bargraph indicate no power.
>>> 
>>> You might want to check D1 and D2 in the KAT100 as well.
>>> 
>>> 73,
>>> Don W3FPR
>>> 
>>> On 5/5/2014 3:09 PM, dl9hda at dl9hda.de wrote:
>>>> Hi,
>>>> 
>>>> my K2 works well but I have issues with my KPA100. KPA100 and KAT100 
>>>> are both situated in an external enclosure but the KAT100 is 
>>>> permanently disabled (cal-mode). I used the KPA100 to drive my 
>>>> tube-amplifier ...
>>>> 
>>>> I cannot exactly say what happend but for a year or so the maximum 
>>>> output power on all bands has been only 60W. It's enough for the 
>>>> tube-pa but now the output is zero.
>>>> 
>>>> If I change the band or hit the antenna-switch the relays are 
>>>> working. So the communication seems to be OK.
>>>> 
>>>> While pressing tune the K2 says high current and there is absolutely 
>>>> no output-power an the K2 and of course at the KPA100. (The K2 
>>>> without any connections to the second enclosure works pretty 
>>>> well!!!).
>>>> 
>>>> So the first guess was to check the diodes D16 and D17. I did not 
>>>> desolder them but I made some measurements with mit Fluke 177.
>>>> 
>>>> D16: Diode-Voltage zero and the other direction shows 0.390 V. The 
>>>> resistor-values are 95.7 KOhms and 104,6 KOhms
>>>> D17: Diode-Voltage zero and the other direction shows 0.387 V. The 
>>>> resistor-values are 95.5 KOhms and 105,2 KOhms
>>>> 
>>> 
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