Analog Control Signals; Keyboard Wiring - Fluke 8842A Instruction Manual

6-56. Hex Inverter (U221)
Check that U221-5 is the same as STROBE ZERO and that U221-6 is STROBE ZERO
inverted.
6-57. Quad OR Gate (U211)
Check U211-6 for 0.2 us pulses, normally high, in two groups of 3 and 15, group widths:
50 and 100 us, group spacing: 10 ms (in fast reading rate).
Check U211-8 for 0.4 us pulses, normally high, groups of hundreds, group widths: 3.5-4
ms, group spacing: about 8 ms (variable).

6-58. Keyboard Wiring

Table 6-19 indicates which waveforms in Figure 6-11 are seen on keyboard inputs to
U212 when each front panel button is pressed and held. For example, if the SRQ button is
pressed and held, an inverted version of STROBE ZERO waveform is applied to U212-
38. If range button "20" is pressed then inverted STROBE ONE is applied to U212-1, and
so forth. Note that these waveforms are very noisy with many spikes. That is normal.
Compare these waveforms with normal STROBE ZERO at U215-8.

6-59. ANALOG CONTROL SIGNALS

SIGNAL NAME
RL0
RL1
RL2
RL3
RL4
RL5
RL6
Table 6-20 is useful for determining whether the correct digital signals are being applied
to the analog control devices indicated. Since most of these devices (the quad analog
switches in particular) have no digital outputs, it cannot be determined directly whether
the correct pattern is being latched. That determination must be made indirectly by analog
means. Nevertheless, it is valuable to know whether the correct digital signals are
reaching those devices.
Table 6-19. Keyboard Wiring
PIN BUTTONS THAT
PRODUCE
INVERTED
(STROBE ZERO)
U212-38 SRQ
U212-39 LOCAL
U212-1 RATE
U212-2 OFFSET
U212-5 20M
U212-6 TRIG
U212-7 EX TRIG
TROUBLESHOOTING
BUTTONS THAT BUTTONS THAT
PRODUCE PRODUCE
INVERTED INVERTED
(STROBE ONE) (STROBE TWO)
20 /mV
200 /mV
2 2 WIRE k
20 4 WIRE K
200
2000
Not used
Maintenance
6
VDC
VAC
mA DC
mA AC
AUTO
6-51