Model 8340A - Service
LBX is an open-collector line that can be pulled down by several
boards. Ql3 provides the open-collector function on this board
and buffers the output of UlOA so that by looking at TP5, the HBX
test point, one can determine if the SWEEP GENERATOR is the board
pulling down on LBX. CR9 is a protection diode for the
base-emitter junction of Ql3, while R45, R46, and CR4 provide
hysteresis for the detector function.
Power Supply Filtering
v
The filtering is the standard low pass configuration. The
particular L and C components were chosen to have a low-Q self
resonance. R48 provides a reference ground for the board in the
event that the connection between reference ground and chassis
ground on the instrument is broken. Ql4 and tBe associated
components create a +15V supply referenced to RGND, This supply
is used to provide symetrical +15V supplies. R49 and R50 divide
the +20V supply down to +l.4V to be used as the comparitor
threshold for comparitors with TTL inputs. All supplies except
+5V and +l.4V are filtered to RGND to prevent digital ground
noise from being injected into the analog circuitry via the power
supplies.
8-373
Scans by HB9HCA and HB9FSX
Содержание 8340A
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