HP 5501B Operating And Service Manual page 85

h. READY LED (green) blinks within 6 minutes, blinks for less than approximately 150
seconds, goes off, and then repeats this action. This indicates that the warmup mode
feedback is not properly controlling the heater voltage. Check the following procedures:
•
A3 Power Amplifier
•
A3 Warm-Up Error Amplifier
• A3 Digital Section
• A3 Subtracting Sample and Hold
i. READY LED (green) blinks within 6 minutes, blinks for less than approximately 150
seconds, come on for one second (twice as long as when it is blinking) then goes off
briefly. This action is then repeated. (An equivalent observation is LTO line [A3U9 (Pin
11)] comes on for 1 second every few minutes). Either the optical mode feedback is not
working or the reference receiver is defective. See Quick Tuning Checkout Procedure,
paragraph 8-64, and Reference Receiver Troubleshooting, paragraph 8-152.
j. READY LED (green) blinks within 5 or 10 seconds, comes on for a few minutes after
approximately 3 minutes, and then starts blinking again. Check A1/ A3 Power Amplifier
section; especially A3U20 and A1Q5-9.
k. Any other READY LED (green) observation indicates a defective digital section. See A3
Digital Section Troubleshooting, paragraph 8-138.
l. If a REFerence frequency signal error is indicated after the laser has successfully
reached normal operation (READY LED on continuously and REFerence frequency
signal output) then make the following observation. Does the READY LED extinguish
when the failure occurs? If so, the optical tuning may be failing or the reference receiver
may be resetting the state machine due to marginal signal strength. Use the Laser Power
Output Test (paragraph 4-11) as a check of the laser assembly and Quick Tuning
Checkout Procedure to get an indication of the function of the optical tuning subsystem
before proceeding with lower level testing. Use the Reference Receiver Troubleshooting
Procedure, paragraph 8-152, to check signal level if the laser assembly and tuning
circuits appear to be functioning properly. If the READY LED does not extinguish,
spurious errors may be occurring on the REFerence frequency signal. Various internal
and external noise or interference may be responsible. Check A3 ground connections
and Vcc coupling capacitors. Check that the HP5501B covers are fastened securely.
Marginal optical signal to the reference receiver may aggravate noise problems. Check
for adequate signal according to Reference Receiver Troubleshooting, paragraph 8-152.
Improper system grounding may also cause noise problems, see
HP5501B
Service
Section 2.
8-25