Figure E-4. LED Display Pin Functions
E-8. Relay Board General Operation
The internal 620A-4R PCB labeled “620-relay
board” replaces the range switch S1 on the main
board. IC-1 is actually a ribbon cable header
that goes to the top panel and connects to the
range push buttons (covered by silicone rubber
boots) and their corresponding panel mount
LEDS. IC-2 is a latch that will latch its output to
the corresponding range push button input. Its
output turns on the front panel LED (acts as an
range mode indicator LED) and a corresponding
relay that connects to the main PCB to select the
range. RL1 is for the 20-Ohm range, RL2 is for
the 200-Ohm range, RL3 is for the 2K Ohm
range, and RL4 is for the 20K Ohm range.
Summary of Contents for 620A 4R
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