HP 8340A Service Manual page 46

4.
CHECK LED I AND II.
The two front panel INSTR CHECK LED's are used to indicate the results of the instrument
Self-Test. A Self-Test is initiated every time the POWER switch is cycled ON or
is pressed. The Self-Test starts by turning both check LED's on.
PRESET]
CHECK LED I will be turned off when it is determined that all ROM and RAM are good and
that the microprocessor is working.
CHECK LED II will be turned off when it is determined that the internal I/O Address Bus
and all 16 bits of the I/O Data Bus are good.
If either one or both of the check LED's remain on, the problem is most likely on the A60
Processor board. Refer to Processor Theory of Operation and Troubleshooting, in the
Controller functional group.
It is possible to have a fault in the instrument that could cause the check LED's to go out
when they should stay on. The check LED's can be double checked by examining the LED's
on the A60 Processor board. If the two INSTR CHECK LED's go off, all 16 Processor board
LED's should be off.
5.
OVEN ANNUNCIATOR
The front panel OVEN light is used to indicate the status of the internal frequency standard.
When the OVEN light is lit, the frequency is more than 100 Hz away from 10 MHz. The A51
10 MHz Reference Oscillator has an internal circuit that monitors the temperature of its
internal oven. When this oven temperature is too low the HOVC line is high
When the oven temperature reaches the desired point (the frequency is within 100 Hz of 10
MHz) HOVC goes low
microprocessor reads it and determines when to turn the light on or off.
The OVEN LED is located on the A 2 Display Driver board (Block
driven by the A3 Display Processor, Annunciator Latch/Driver.
The LED is turned on by the instrument processor. The processor outputs the appropriate
bits on the Data Bus and then outputs address 15:RO to latch the data bits.
6.
UNLK ANNUNCIATOR
The UNLK light is used to indicate the status of the 6 different internal phase lock loops. If
the UNLK light is on, one or more of the loops is unlocked. Press
ENTRY DI SPLAY will show the following:
O SC: REF M/N HET YO N2 Nl
The name of the loop that is unlocked will be flashing.
REF - If the REF is flashing, refer to the Reference Loop Theory of Operation and
Troubleshooting in the Reference Loop - M/N Loop functional group.
M/N - If the M/N is flashing, refer to the M/N Theory of Operation and Trou­
bleshooting in the Reference Loop - M/N Loop Functional group.
HET -
If the HET is flashing, refer to the RF Section (AS 3.7 GHz Oscillator) Theory
of Operation and Troubleshooting.
YO - If the YO is flashing, refer to the YO Loop Theory of Operation and Trou­
bleshooting in the Sweep Generator - YO Loop functional group.
Nl - If the Nl if flashing, refer to the 20/30 Loop (PLL l ) Theory of Operation and
Tro"ubleshooting.
N2 - If the N2 is flashing, refer to 20/30 Loop (PLL2) Theory of Operation and
Troubleshooting.
Model 8340A - Service
15V). HOVC is sent to the A59 Digital Interface board where the
O
+
Scans by HB9HCA and HB9FSX
[INSTR
·
15V).
(> +
These LED's are
E).
[SHIFT] [EXT].
The
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