[Elecraft] KPA100 Problem

[Mark Flavin]

Thanks Don.  This thing worked before I did the upg kit.  I will check that  
again but I didn't really touch those.  Perhaps I will remove the   Q3 and  
check that area.  Best I can tell the upgrade didn't really address any of  
that but I don't know.  The finals don't get hot at all.  I even took the  
heatsink off to make sure there were no shorts or anything and its the same.  
  The weird thing is how the fan starts and stops as I key even at low (11  
to 15 watts) power.  I just hope its not the finals.  I don't think so  
either but I want to try everything else first.  Could Q3 just be too  
sensitive due to something.  I could try changing it I suppose.

T-Mobile. America's First Nationwide 4G Network.

-----Original message-----
From: Don Wilhelm <w3fpr at embarqmail.com>
To: Mark Flavin <markf1952 at hotmail.com>
Cc: elecraft at mailman.qth.net
Sent: Sat, Nov 26, 2011 19:00:07 GMT+00:00
Subject: Re: [Elecraft] KPA100 Problem

Mark,

I don't think the finals are the problem.  I would check Q3 for good  
soldering and the value and soldering of R5 - make certain you used the 1k  
trimmer at R6 rather than the 100k trimmers for R26 and R27.
The soldering at U1 pin 5 should also be checked, and be certain U1 pin 5 is  
not bent under the socket or sticking out the side.  Make certain there is 5  
volts on one end of R5 - if not, find out why.

The temperature of the heatsink is sensed by the conduction through Q3 from  
the base to the emitter (and collector),  that resulting voltage is sent to  
U1 pin 5 for calculation by the firmware  - it has nothing to do with the  
actual PA transistors, just the temperature of the heatsink at the Q3  
location.

73,
Don W3FPR

On 11/26/2011 1:04 PM, Mark Flavin wrote:
> Yeah. I did that too.  Im dreading changing the finals lol
>
> T-Mobile. America's First Nationwide 4G Network.
>
> -----Original message-----
> From: Don Wilhelm<w3fpr at embarqmail.com>
> To: Mark Flavin<markf1952 at hotmail.com>
> Cc: elecraft at mailman.qth.net
> Sent: Sat, Nov 26, 2011 17:45:04 GMT+00:00
> Subject: Re: [Elecraft] KPA100 Problem
>
> Mark,
>
> Have you checked the setting of the K2 CAL TPA menu?  It should read the
> same as the actual temperature of the PA transistor cases.
>
> Let everything acclimate to the ambient room temperature (power off for 30
> minutes should do it), then turn power on and set CAL TPA to the room
> temperature in degC.
>
> 73,
> Don W3FPR
>
> On 11/26/2011 11:44 AM, Mark Flavin wrote:
>>
>>
>> Well, I wanted to change the bridge diodes in the KPA 100 cause I was
> getting some wierd readings and hi swr readings so I decided to upgrade it
> while I had it apart.  I did the whole upgrade and now as soon as I put it
> in high power, even at only 15 watts, I get PA HOT readings.  I have  
checked
> all the parts values twice and did the calibration again including the C6
> adjust, the r26 and 27 adjusts and even pulled the finals to make sure  
they
> weren't shorted or anything.  Q3 and Q4 seem fine and are not cracked.   
The
> voltages seem to be fine and I readjusted R6 bias as per book.  Whats  
wierd
> is as soon as I hit the key, even at 15 watts the fan comes on with the
> keying.  A dot gives a short fan wiggle and an dash gives a loneger fan
> activation.  Eventually it comes on and then I get the PA HOT.  The fan  
even
> responds to my voice on SSB.  I mean it comes on almost instantly.  I have
> checked the archives and am starting to suspect the finals.  I put on new
> pads on the transisto
>>    rs and checked it all twice.  Resoldered all connections.  All works
> fine at 10 watts.  Im sure Im missing something but I dont seem to be able
> to find it.  Any ideas where I can check before I order new finals and go
> through that work again.  Thanks  MarkN5MF 		 	   		>
>
>
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