HP 5501B Operating And Service Manual page 100

m. With settings same as step I, check that U4 pins 1, 2, 9, 12, 13, and 16 are all high. If not,
U4 is bad. At this point, the digital section should be OK.
n. Set REF ON to HI, HTR OK to "X", and ALL other jumpers to left. U9 (Pin 13) (HTRQ)
should be high. If not, check U8A. If so go to step o.
o. Keep ~REF ON to HI, set HTR OK to LO. U9 (Pin 13) (HTRQ) should be low. If not, U8A
is bad. If so, go to step p.
p. Set ~REF ON to LO. U9 (Pin 9) (POR) should be low. If not, U2B is bad. If so, go to step
q.
q. Turn the power off. Set ~REF ON to HI, HTR OK to HI, HEATER to NRM. Check that U9
(Pin 9) comes on then blinks at a few Hz or so at power on. If OK go to step r. If not,
replace C1 and check CR1, R5A, R51, and R48A.
r. Return HTR OK and ~REF ON jumpers to NRM. The READY LED should start blinking in
a minute or two. If yes, go to step s. If no, check A1R18 and A1DS8.
s. Turn power off. Set ~REF ON to HI. Set POWER AMP jumper to UP. Turn power on and
allow the laser to run for five minutes. Observe the voltage level at U2C Pin 8 with an
oscilloscope. Pin 8 will be at TTL low and will periodically go high (>2.4 Vdc) for a few
seconds (approximately 2seconds). The laser head will go through the following cycle
and can be monitored by observing the rear panel READY and LASER ON (or the
corresponding LED's mounted on A3) and the oscilloscope display. The cycle begins
with both LED's off and the voltage at U2C (Pin 8) at TTL low. The READY LED begins
flashing and continues to do so for approximately 150 seconds. About 100 seconds into
the cycle the laser beam and the LASER ON LED turn on. The READY LED continues to
flash. After 150 seconds, the READY LED stops flashing and remains on steady. Both
LED's remain on only momentarily. At this point, the DISABLE line goes high, and the
laser beam and both LEDS turn off. This cycle is repetitive with the test jumpers set as
they are. If the cycle occurs as described, remove power return all jumpers to their NRM
position. The Digital section is OK. If Pin 8 doesn't go high, check divider and state
machine circuitry. See A3 Power Amp section for additional information.
t. Signature Analysis:
WHEN TAKING SIGNATURES, ENSURE THAT THE TEST-NORM
SWITCH (A1S2) IS SET TO NORM AND THAT HEATER TEST
JUMPER IS IN THE OFF POSITION. DAMAGE TO THE HIGH
VOLTAGE POWER SUPPLY OR LASER ASSEMBLY COULD RESULT
IF THESE INSTRUCTIONS ARE NOT ADHERED TO.
With the power (±15 Vdc) disconnected, set the HP5501B switches and test jumpers as
follows:
TEST-NORM = NORM, HTR OK = HI, ~REF ON =HI, RESET=TEST, CLK FREQ =
Remove, HEATER = OFF; TP2, TP3, and Pin "X" of HTR OK jumper to ground.
Connect the signature analyzer (HP5005A/B) test pod leads as follows:
Set signature analyzer front panel controls as follows:
CLOCK, START, and STOP Polarity set for falling edge.
8-40
START = A3TP7, STOP = A3TP6, CLOCK = A3TP5, GND = A3TP4
HP5501B
Service