K2 KPA100 overheating/erratic fan problem

[Elecraft mailing list]

Hello,

I wonder if anybody had similar problem.
When I “run” I get fan starting running after 10-15 minutes. However after another few minutes of running the fan will shuts down every time I press a key ( I am CW op). As a result the temperature of the PA goes higher and higher and at certain point the PA shuts down. If I check the temperature reading through temperature calibration in the menu I see that temperature reading jumping force and back with range of readings 10 - 20C. That kind of erratic temp reading continues even when temperature of the heatsink goes down. If let the trcv to cool (overnight) the temperature readings are stable with range of reading +- 1C.

I check soldering and mounting - if there were problem they were fixed. But no results so far. I also upgraded the PA a week ago and that did not have effect on the overheating.

Any input will be appreciated.

73, Arkady
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[Jim Brown-10]

On 11/30/2020 2:00 PM, Arkady via Elecraft wrote:
> When I “run” I get fan starting running after 10-15 minutes.

This happens to me when "running" with few callers on CW, sooner on
RTTY, and within 5 minutes or less with WSJT modes. I've not experienced
the other behavior you describe.

73, Jim K9YC


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[Don Wilhelm]

Arkady,

Is Q3 properly seated on the heatsink with its thermal pad and mounting
screw?  That is the device which senses the temperature.

73,
Don W3FPR

On 11/30/2020 5:00 PM, Arkady via Elecraft wrote:
> Hello,
>
> I wonder if anybody had similar problem.
> When I “run” I get fan starting running after 10-15 minutes. However after another few minutes of running the fan will shuts down every time I press a key ( I am CW op). As a result the temperature of the PA goes higher and higher and at certain point the PA shuts down. If I check the temperature reading through temperature calibration in the menu I see that temperature reading jumping force and back with range of readings 10 - 20C. That kind of erratic temp reading continues even when temperature of the heatsink goes down. If let the trcv to cool (overnight) the temperature readings are stable with range of reading +- 1C.
>
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[Elecraft mailing list]

Hi Don,

Yes, it does have a good pad and is properly attached to the heatsink. I was upgrading the KPA and re-soldered both Q3 and U1 temperature sensing contacts as well as verified that Q3 installed properly. But that did not change anything.

73, Arkady
On Dec 1, 2020, 11:18 AM -0800, Don Wilhelm <[hidden email]>, wrote:

> Arkady,
>
> Is Q3 properly seated on the heatsink with its thermal pad and mounting
> screw? That is the device which senses the temperature.
>
> 73,
> Don W3FPR
>
> On 11/30/2020 5:00 PM, Arkady via Elecraft wrote:
> > Hello,
> >
> > I wonder if anybody had similar problem.
> > When I “run” I get fan starting running after 10-15 minutes. However after another few minutes of running the fan will shuts down every time I press a key ( I am CW op). As a result the temperature of the PA goes higher and higher and at certain point the PA shuts down. If I check the temperature reading through temperature calibration in the menu I see that temperature reading jumping force and back with range of readings 10 - 20C. That kind of erratic temp reading continues even when temperature of the heatsink goes down. If let the trcv to cool (overnight) the temperature readings are stable with range of reading +- 1C.
> >

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[Elecraft mailing list]

Hi Don,

I think I tracked the problem and I would like to document it for future generations :).
I noticed that during SKCC events I don’t have the issue. In the following  contest instead of using internal keyer though serial port I switched to an external keyer and sure enough the issue did not surface. That brought me to a serial port cable that was provided by the previous owner of the K2. I found that the cable was just a standard serial extension cable. I quickly made a makeshift serial per Elecraft recommendation and was not able reproduce the problem with the correct cable. I ran the K2 in Winter RAC and it worked as intended. I am happy that I did not fry a chip with the wrong cable but apparently wrong cabling may introduce a quite strange side effect that makes the chip work incorrectly when it is under the temperature pressure.

73, Arkady/NU6N
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[Don Wilhelm]

Yes, a standard serial cable plugged into the AUX IO connector will
cause "strange happenings".

73,
Don W3FPR

On 1/6/2021 2:27 AM, [hidden email] wrote:

> Hi Don,
>
> I think I tracked the problem and I would like to document it for
> future generations :).
> I noticed that during SKCC events I don’t have the issue. In the
> following  contest instead of using internal keyer though serial port
> I switched to an external keyer and sure enough the issue did not
> surface. That brought me to a serial port cable that was provided by
> the previous owner of the K2. I found that the cable was just a
> standard serial extension cable. I quickly made a makeshift serial per
> Elecraft recommendation and was not able reproduce the problem with
> the correct cable. I ran the K2 in Winter RAC and it worked as
> intended. I am happy that I did not fry a chip with the wrong cable
> but apparently wrong cabling may introduce a quite strange side effect
> that makes the chip work incorrectly when it is under the temperature
> pressure.
>
> 73, Arkady/NU6N

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