[Elecraft] Diode check: Thanks, got answer

Sat Aug 3 18:58:01 2002

Don, Leo et al - 
Thanks for the help guys. I decided to buy a better mouse trap since I
found they were on sale at Rat Shack and got a DMM with a diode check
built in. All diodes are good and I learned a new lesson. Thanks folks! 

73, Tim NZ7C

Don Brown wrote:
> 
> Hi
> 
> DVM's measure resistance by applying a constant current to the circuit and measuring the voltage drop across the leads. On some ranges the applied voltage is less than the turn on voltage for a diode so these ranges cannot be used to check a diode. The ranges that will turn on a diode are usually marked on the meter with a diode on the range switch (usually 1K range) Even though you are on ohms the reading will indicate the voltage drop of a diode when the leads are connected so the diode is foward biased. Some meters will have a special diode checking range to do this if not try measuring a diode out of circuit on each ohm range. Look for a range that measures about .600 with the diode connected forward and over range reversed
> 
> Don Brown
> KD5NDB
> 
> ----- Original Message -----
> From: Tim and Nancy Logan
> Sent: Saturday, August 03, 2002 4:26 PM
> To: Elecraft
> Subject: [Elecraft] KA100: "diode check scale"?
> 
> Hi Folks - I don't understand the expression "diode check scale" on page
> 14 of the amp manual. If I use the voltage scale none of the readings
> seem to be in the ranges required. However, I did make the following
> resistance measurements:
> 
> D1 - D8 .6M ohm (red lead on anode) and infinite (OL)  (black lead on
> anode)
> D9 - .4k ohm                            316k ohms
> D10 - 4.7M ohms                         infinite (OL)
> D11 - .67M ohms                         infinite (OL)
> D12 - .57M ohms                         infinite (OL)
> D13 - 4.2M ohms                         infinite
> D14 - .57M ohms                         infinite
> D16 & D17  - 51k ohms                   infinite
> 
> If I assume that OL means no resistance, this would suggest the diodes
> are all OK (except for D9?). Can someone explain how to use the DMM to
> check
> the voltage? Will my resistance checks suffice?
> 
> Regards, Tim Logan NZ7C
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