[Elecraft] K3 Hi-power Transmit limiting

[Keith]

Sounds like maybe the LPA has a problem. Try the following test;
With the bottom back cover off, radio powered up.
If you have a FLIR camera watch the 3 LPA FETs.
If not, put a finger on each and TAP (not push and hold) the XMIT 
button,,,, They should start to get hot EVENLY! Takes 5 or 10 seconds, 
Take fingers off when it is too hot for you and tap the xmit to stop the 
test.
If they are even, then they look OK, if not even, the COOL one(s) are 
bad. Most likely Q4 and Q5.
Replace, re-bias put the bottom cover on, and do the 5w gain cal.
Keith

On 2/13/2012 4:17 PM, Keith wrote:
> One would initially think of a power supply problem, I found out an
> Astron RS-20 is insufficient.
> But "new firmware" was mentioned, the latest is 4.39 (non-beta), Are
> either of you using a new Beta version?
> Keith
>
> On 2/12/2012 3:14 PM, n6ax at speakeasy.net wrote:
>> Latest firmware, just did TX cal a few weeks ago, same things happens whether on
>> antenna or dummy load, PS not dropping, mine drops to essentially zero output
>> above about 88 watts.
>>
>>
>>
>>
>>
>> anyone....Buehler....anyone?
>>
>>
>>
>>
>>
>>
>>
>>
>> On Sun Feb 12 15:05 ,  sent:
>>
>>> Mine just started that behavior yesterday as well.....the oddest thing...any
>>> ideas, guys?
>>>
>>>
>>> John
>>>
>>>
>>>
>>>
>>> On Sun Feb 12 13:38 , r_zerr  sent:
>>>
>>>> I began having problems this morning when I went to check into the Elecraft
>>>> Net. I had my output set at 100W, and I did not have any output. By turning
>>>> it down to around 70 watts, I could transmit.
>>>>
>>>> I went through the transmit gain calibration on 20M and the Wattmeter
>>>> calibration, with apparent changes in the Wattmeter reading (initially at
>>>> 31, now at 79...50W into Dummy load, Bird Wattmeter, 100W slug). The
>>>> Transmitter gain changed only slightly, 16 to 17, but is more of a choice
>>>> between high-side, or low side of the meter reading.
>>>>
>>>> Checked and Bat Min setting is at 11.0V and the KXV3 setting is normal
>>>>
>>>> Other info in present condition: 20M>90W kicks off. 20.4A draw at 90W PA
>>>> temp=33C Voltage @load=12.4V
>>>>
>>>> I checked the behavior on 17M with similar problems, kicks off above 96W
>>>> setting, with 12.8V, 14.3A draw
>>>> 15M kick of above 96W, with 12.6V @ 17.8A
>>>> 12M kicks off above 97W, with 12.8V @ 14.1a
>>>> 10M kicks off above 97W  with 12.9V @ 13.6A
>>>> 30m kicks off above 98W with  12.6V @ 16.5A
>>>> similar results on 40m and 80m
>>>>
>>>> Before I go pulling the top off and checking connections, does anyone have
>>>> any suggestions?
>>>>
>>>>
>>>> -Ron, WT5RZ
>>>>
>>>>
>>>> --
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>>>> Sent from the Elecraft mailing list archive at Nabble.com.
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