K2 RF Detector

[Julius Fazekas n2wn]

I've moved along, (thanks Don) with my problem. It
looks like I have a RF voltage at the input of R67
(1.5K 1%) but nothing on the other side. No DC voltage
at D9. What should I be seeing in this area. I was set
for 2 watts or a bit less...
Thanks,
Julius
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[Don Wilhelm-2]

Julius,

Recall that the RF voltage at one end of D9 will be only 1/8 of the voltage
at the other end - this is a resistive voltage divider.  You really didn't
say how much RF voltage you had, so go on and check things out as follows:

First unplug the KPA100 and KAT100 and re-check.  When the KPA100 or KA100
is installed, the K2 does not use the simple RF detector on the RF board,
but instead uses the wattmeter on the KPA100 (or KAT100).  That does NOT say
that D9 is good though, so go ahead and check things out as below since it
is not very difficult.

If I had the same situation here, I would still remove D9 and test it out of
circuit (diode test on you DMM if it has one, resistance check if it does
not - it should conduct one way but not the other).  Best bet is that D9 has
popped on you, but it is possible a resistor has opened instead.

Before replacing D9, I would check resistance on the RF board to be certain
all is OK - from D9 anode, you should read 226 ohms to ground and 1.5 k to
the antenna jack; from the D9 cathode pad you should read 100k to ground and
2.7k to pin 10 of P4 on the control board (Aux I/O connector).

If everything above checks out good and D9 checks good, the only thing left
is the path on the Control Board - 820 ohms between P4 pin 10 and U6 (MCU)
pin 2.  Also check the resistance from P4 pin 10 to ground - it should be
greater than 100k.

If D9 is bad, you can temporarily replace it with a 1N4148 or similar if
that is on hand.  The 1N5711 gives more linear power readings, but most any
silicon diode will work.

If all the above checks out and the problem remains, look at the VRFDET
circuitry in the KPA100 and KAT100.

73,
Don W3FPR

----- Original Message -----

> I've moved along, (thanks Don) with my problem. It
> looks like I have a RF voltage at the input of R67
> (1.5K 1%) but nothing on the other side. No DC voltage
> at D9. What should I be seeing in this area. I was set
> for 2 watts or a bit less...
> Thanks,
> Julius
>


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[Don Brown-4]

Hi

If the K2 will work properly with the KPA100 removed and the DC voltage is back on the VRFDET line then you may have a bad U6 in the KPA100. This IC is a tristate op amp and if bad will load down the VRFDET line. I have found several of these IC's bad with the symptoms you are describing. The IC can be zapped if a greater than 5 volt signal is applied to the VRFDET line. This could be caused by a miswired 9 pin D RS232 or data connector or by static discharge. It may be a good idea to add a couple of diode clamps to the VRFDET line on the KPA100 to protect this IC. Maybe Wayne should give us some direction here.


Don Brown  (the other Don)

KD5NDB
  ----- Original Message -----
  From: J F<mailto:[hidden email]>
  To: [hidden email]<mailto:[hidden email]>
  Sent: Saturday, July 31, 2004 5:50 AM
  Subject: [Elecraft] K2 RF Detector


  I've moved along, (thanks Don) with my problem. It
  looks like I have a RF voltage at the input of R67
  (1.5K 1%) but nothing on the other side. No DC voltage
  at D9. What should I be seeing in this area. I was set
  for 2 watts or a bit less...
  Thanks,
  Julius
  _______________________________________________
  Elecraft mailing list
  Post to: [hidden email]<mailto:[hidden email]>
  You must be a subscriber to post to the list.
  Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft<http://mailman.qth.net/mailman/listinfo/elecraft>    
  Help: http://mailman.qth.net/subscribers.htm<http://mailman.qth.net/subscribershtm>
  Elecraft web page: http://www.elecraft.com<http://www.elecraft.com/>
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