[Elecraft] Control board resistance checks on K2, help a newbie please!

[Don Brown]

Hi

There is a lot of variation in the way DVM manufacturers measure ohms. The voltmeter in some of the meters will flash for an over range others will display OL for overload. Some will blank the display with only the left most digit displaying a one. Don't be concerned about the term overload it is not hurting anything. A better name is OR for over range but that is not what they use because it is easier to form a OL than a OR with a seven segment display. Anyway to measure ohms the meter will try to force a constant current across the meter leads and measure the voltage drop. This is directly proportional to the resistance of the circuit unless the resistance is high enough to cause the voltmeter to read over range. To change ranges the constant current generator is changed to force a different current. This is why some ranges will turn on a semiconductor and others will not. The bottom line is if the resistance in the manual calls out a resistance greater than some value and your meter reads over range on a range that can measure that resistance then you are ok. What you are mostly looking for is gross errors like shorts when making resistance checks. The voltage tests are more meaningful. They should be very close to the manual call outs within 5- 10 %.

Don Brown

KD5NDB


  ----- Original Message ----- 
  From: Jason Marten<mailto:martenjj at hotmail.com> 
  To: elecraft at mailman.qth.net<mailto:elecraft at mailman.qth.net> 
  Sent: Saturday, August 28, 2004 5:59 PM
  Subject: [Elecraft] Control board resistance checks on K2,help a newbie please!


  Hi everyone,

  I'm trying to do the resistance checks at the end of the control board part. 
    A lot of the values seem right, but I'm not sure about some of them.  Due 
  to inexperience in kit building and using a DMM, I may just be reading 
  things wrong (I have built a couple of small kits).

  For Q1 collector, Q2 collector, U6 pin 13, U6 pin 14, U8 pin 15 and U8 pin 
  16, I get a reading of "0L" on my BK Tool Kit model 2704B DMM.  This is the 
  value that's normally displayed when you turn the knob to measure resistance 
  and have an open circuit (i.e. the test leads aren't connected to anything). 
    Does this mean I have an open circuit somewhere, or is the 0L mean 
  infinite resistance (which would be OK on the checks)?  The K2 manual says 
  some DMM's will flash for infinite resistance.  I have never seen my DMM 
  flash, and I can't find anything about flashing or OL in the manual.  Or, 
  are there other places to look to make sure I've done things right?  
  Everything appears fine based on a visual inspection (to my untrained eyes, 
  at least).

  Otherwise, values for P2 pin 1, U5 OUT, U4 OUT, U3 pin 8, U6 pin 29, U6 pin 
  30, and U8 pin 2 seem correct.  Actually, for P2 pin 1, my DMM starts off in 
  the negative and then continues to increase at a slow rate.  Is this normal?

  Thanks for the help.

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