HP 437B - ANALOG BOARD TROUBLESHOOTING

HP 437B
Service Sheet BD1
23.
Using
the
logic
probe
or
oscilloscope,
check
for
a
logical
high
(>+2.5V)
at
A4U16,
pin
19
(on
Service
Sheet
A4c).
24.
If
the
signal
at
A4U16
pin
19
is
a
logical
high,
turn
to
Service
Sheet
Adc
and
troubleshoot
either
the
50
MHz
Reference
Oscillator
or
the
Power
Reference
Switch.
25.
If
the
signal
at
A4U16
pin
19
is
not
a
logical
high,
turn
to
Service
Sheet
A4c
and
troubleshoot
the
Microprocessor
Control
circuit
or
the
ribbon
cable
assembly
W6.
Analog Board Troubleshooting
Microprocessor Control Circuit Verification.
1. Press the Power Meter’s PRESET/LOCAL key.
2.
Connect
the
range
calibrator
to
the
Power
Meter’s
SENSOR
connector.
a For steps 3 through 12, refer to Figure 8-3. 5
Note @
3. Using a logic probe, verify the presence of TTL signals at A4U16 pins
3, 4, 7, 8, 12-18 and A4U18 pins 7, 9-13.
4. Set the Power Meter’s POWER REF to off.
5. Verify a logical low level (<80V) at U16, pin 19 (CALOSC).
6. Press the Power Meter’s SET RANGE key. Select range 3.
7. Verify a logical high level at A4U16 pin 6 (NATTEN).
8. Press the Power Meter’s SET RANGE key. Select range 4.
9. Verify a logical low level at A4UI6 pin 6.
10. Verify a logical high level at A4U16 pin 2 (NSLOW) and a logical low
level at A4U16 pin 5 (NFAST).
11. Press the SET RANGE key. Select range 1.
12. Verify a logical low level at A4U16 pin 2 (NSLOW) and a logical high
level at A4U16 pin 5 (NFAST),.
@
8-32 SERVICE