Theory of Operation
2715 Spectrum Analyzer Service Manual 3-87
5. After the firmware recognizesthe request for service, the FPACK--line is set
low, which enables the DATAI and CLKI tristate buffers.
6. The data is then clocked out ofthe switch matrix shift registers.
7. After the data has been clocked out, the FPACK-- line is set high, disabling
the DATAIand CL KI tristate buffers.
8. The rising edge of FPACK-- is also used to reset the request for service flip
flop.
9. The board is now ready foranother key press.
There are two diagnostic tools available forthe front panel, the key test and the
LED test. These diagnostic tools reside in instrument firmware. They are used
during initial board turn on and when thefront panel needs repair. Descriptions
for these diagnostic tools follow.
Key Test.The key test is located in the extended diagnostics menu of the
instrument and consists of text prompting thetechnician on which key to press.
If the correctkey is pressed, its location in the switch matrix and the next switch
to be pressed are displayed. If the incorrectkey is pressed, the speaker beeps, and
the same key press is prompted again. Up t o four incorrect key presses are
allowed before the firmwarecontinues on to the next key.
LED Test.The LED test is also located in the extended diagnostics menu of the
instrument and uses the knob to light each LED one at a time, in a known
sequence. By rotating the knob, each LED is lit. The test runs until the backspace
key is pressed.
Power Supply (Primaryand Secondary)The Power Supply operates with a line input voltage from 90 VACto 250 VAC
without range switching. This is done by regulating therectified AC input
(125 V to 350 V) to 60 VDC.
An inverter drives a transformerhaving numerous secondaries, including a high
voltage winding (1400 V peak) for the CRTsupplies. The secondary voltages are
rectified to provide operatingpower for the instrument.
The high current secondaryoutput, +5 V, is regulated by feedback to the primary
pulse width modulator.The other secondary outputs track +5 V fairly closely,
except for the high voltage supplies, which have secondary regulation.
The Power Supply circuits are dividedinto the primary circuits and the
secondary circuits.