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

[Don Wilhelm]

Holger,

I didn't think of it before the last response, but be certain you are 
using the correct Diode Voltage chart.
If you have a newer KPA100 or one that has been upgraded - with blue 
toroid cores at RFC1 and L15, then you must use the newer voltage chart 
(download the most recent KPA100 manual).
With the newer design, the only place you will find a high voltage is at 
the cathodes of D12 and D14.

OTOH, if you had red toroid cores at L15 and L16, you have the older 
KPA100 and the Diode Voltages in your manual should be correct.

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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