Stanford Research Systems SR620, Manual

Page: 73 / 124

Troubleshooting Tips 57
SR620 Universal Time Interval Counter
TROUBLESHOOTING
To start, make sure that the power entry module
on the rear panel is set for the ac line voltage for
your area, that the correct fuse is installed, and
that the line cord is inserted all the way into the
power entry module. The selected line voltage
may be seen through the clear window, just below
the fuse.
When the unit is plugged in and turned "ON", the
unit's model number, firmware version number,
and serial number will be briefly displayed. Then
the message, "SELF TEST...PASS" should be
briefly displayed.
If the unit displays no sensible message, the "cold
boot" procedure may fix the problem. To do a "cold
boot", turn the unit off. Then, while holding the
"RESET" button in the SAMPLE SIZE section
down, turn the unit "ON". This procedure initializes
the RAM and recalls all factory calibration values.
The "Autocal" procedure should be run after the
unit warms up. (See below)
If the message "code error" appears it indicates
that the SR620's ROM has an error and the unit
should be sent back for repair.
If a Test Error message appears, you may be able
to fix the problem with the unit's internal calibration
routines.
Test Error
Problem
3
Lost Memory
4 Cpu Error
5 System RAM error
6 Video RAM error
16 Count gate error
17,20 Channel 2 counter
18,19 Channel 1 counter
32 Frequency gate
33 Excessive jitter
34 Insertion delay, Freq.
35 Insertion delay, Time
Any of these errors may be caused by a hardware
failure which will require repair.
Test error 3 is usually "self-healing". The
instrument settings will be returned to their default
values and factory calibration data will be recalled
from ROM. Test Error 3 will recur if the Lithium
battery or RAM is defective.
Test errors 33 to 35 may be corrected by the
"Autocal" procedure. To run this procedure, press
the SEL button in the CONFIG section to select
"cAL". Press the SET button once choose "Auto
cAL". Then press the START button in the
SAMPLE SIZE section to begin the autocal
procedure. This procedure may not be started until
the red CLOCK LED in the CONFIG section goes
off, otherwise a cAL Error 01 will result. The
autocal procedure takes about two minutes to run,
and ends with the message "cAL donE", the
SR620 then returns to taking measurements.
If the UHF prescaler of channel A is selected when
the unit is powered off and then on again, the unit
will display “TEST ERROR 34”. This error may be
corrected by deselecting the UHF of channel A. To
run this procedure, press input button of channel
“A” until UHF is not highlighted. Then turn the
power off and on again.
Other cAL Errors flag hardware problems per the
table below:
Cal Error Problem
1 Not warmed-up
2 No trigger
3-7 Start TAC
19-23 Stop TAC
The Start and Stop TAC's (Time to Amplitude
Converters) are the circuits which perform the
analog interpolation between the 90 MHz clock
ticks. The autocal procedure sets the gain and
linearizes the transfer function of the TAC's.
COMMON OPERATIONAL PROBLEMS
Error Messages
countEr oFL Time interval has exceeded
1000 seconds, or frequency
exceeds 1.5 GHz, in x1000
mode period > 1s or
frequency >1MHz
rAtio oFL Ratio result exceeds 1000
dividE by 0 Denominator = 0 in ratio
measurement