HP 5305 B Operating And Service Manual page 28

9E-5-40. If the reserve is true, i.e., the frequency at U22(3) is
greater than U22(1), then U22(2) should pulse low (or stay
low if nothing at pin 1). and U22(13) should always be high.
Pins 2 and 13 can never be low together.
9E-5-41. "S" LIGHT ON, NO MEASUREMENTS. It is
possible that the PLO is working properly but no
measurements are made. If the negative edges of the signals
at U22(1 and 3) match, the PLO is working properly. U22(2
and 13) should be high almost all the time, and U24(6) should
be low almost always (small positive pulses). Then U16(1)
(LOST) should be at TTL 1 (+5 volts). If not, there is
something wrong with it or associated parts R77, R78, R59,
R61, R62, R70 or R36. Also, U18(10) (STOP) should be low.
When STOP is high, counter operation is frozen by stopping
the clock at U10(13), and the "S" light is lit.
9E-5-42. FAULTY DISPLAYS WITH NO INPUT. When
the input is disconnected, the display should hold last reading,
if not check the stop circuits (U24, U16, and U18).
9E-5-43. INCORRECT FIRST READING. The first
measurement after a signal is applied should be accurate. If
way off, the reset circuit Q19 is not working. About 1/2
second after a signal is applied, U18(10) should go low,
U24(3) should go high and Q19 should saturate for about
1/10 second. This should pull J1-32 (50 pin connector) low
and the system should "manual reset".
All 8's should show in the display (5300B) for 1/10 second,
then 0's until new measurement displayed at end of gate time.
If not, there are problems around Q19, R91, R92, R93 or C48.
9E-5-44. SLOW ACQUISITION. If the 5305B takes more
than about 1 second to make a measurement (plus gate time)
after a signal is applied to the PLO, circuit problems exist.
With no signal, check that U16(1) is low (LOST). U18 should
be enabled, and low rate (25 Hz) pulses should appear at
U18(1) (same as of U22 pin 2). Connect a 20 kHz signal and
check for pulses at U18(13). The S light should be on during
this time. Check CR16 and CR18. If CR24 (a tri-diode) is
open, tuning will be slow and the upper frequency limit will
be very low. If CR20 and CR22 are open, the loop will be
slightly erratic.
9E-5-45. NOT ENOUGH RANGE (10 kHz). If the PLO
will not measure high frequencies (10 kHz). check CR24 and
ensure proper values of R83, C42, and C47. The tuning
voltage at U23(6) should be about +4V at the highest
frequency. Also, check the + 12V supply.
9E-5-46. POOR LOW-FREQUENCY RANGE. If the
counter does not measure low frequency (50 Hz). check Q16
for leakage. Ensure that U23(6) can pull voltage high enough
(Q16 should be off at the lower frequency limit). Check C49,
C47, and CR21 and check for +1.5V at U23(3).
Model 5305B
Maintenance
9E-5-9