[volt-nuts] 845ab Led Mod Update

Dallas Smith dosmith at outlook.com
Wed Sep 24 15:06:04 EDT 2014

Well I finally got the 615nm Led's installed and the results seem so so. 
The zero drifted was significantly on the 1uV range. So I used two 
LT1634 1.25 Volt references with the current set by two 43k resistors 
from the ±15 volt supplies. The previous reference used came from the 
-0.4 volts at TP1 and +0.6 volts at TP8. Removed the 150k resistor at 
the positive end of the zero control and lifted the negative end from 
the circuit board the connected the ±1.25 ref to the zero pot. Much 
better stability, drifts by noise about  ±.1 to ±.2uv now on 1uv range. 
Is this normal now? Never used a new Fluke 845ab before. The white led's 
seemed to filter the noise better with its persistent, may go back. The 
zero seems stable with ±2 F change in room temperature now.

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