Table 8-3. Ic A3U4 And A3U6 Divider Check - HP 5501B Operating And Service Manual

If these are OK, go to step n.
If the signature analyzer will not take signatures, then there is a malfunction in the
dividers or power on-reset sections go to step e.
If the signature analyzer works, but one or more signatures are wrong, go to step f.
e. Set HTR OK to HI, REF ON to HI, and RESET to TEST. ConnectTP2, TP3, and pin X of
HTR OK jumper to ground (TP1 or TP18). Verify the dividers by measuring the
frequencies at the IC pins indicated in Table 8-3 and determine if they are equal to the
indicated ratios, i.e. the frequency at U6 (Pin 13) should be equal to the frequency at TP5
divided by 16. Note: The counter function of the signature analyzer may not work so a
dedicated counter might be needed.

Table 8-3. IC A3U4 and A3U6 Divider Check

Measure Frequency
at
IC Pin
U6 13 =
U4 15 =
U4 1 =
U4 7 =
If no problem is found, proceed to step f.
f. Set HTR OK to HI, ~REF ON to HI, RESET to TEST. Connect TP2, TP3, and Pin "X" of
HTR OK jumper to ground. (TP1 or TP18). Set up the signature analysis clock, start, and
stop signals for falling edge detection. Using the signatures listed in step t; localize the
defective element by using standard signature analysis troubleshooting. Begin with U9
and use the schematic to trace back faulty signals. Check U1 (Pin 6), U19 (Pin 10), and
U2 (Pin 6) right away, they are critical points. If no trouble is found, go to step g.
g. Remove ground connection on HTR OK jumper. Is U8 (Pin 6) signature 05C5? If not,
U8A or R48B is faulty. If so, go to step h or see Warm-Up Error Amplifier
Troubleshooting.
h. Remove the ground connection on TP3 and leave off. Is the +5V signature (TP9) CP5P?
If not, go to step i. If so go to step k.
i. Set HTR OK to LO. Is U8 (Pin 5) low? If not, U8 is bad. If yes, go to j.
j. Is TP3 high? If yes, go to k. If no, check U4B, U5D, U19D, and R5D.
k. Remove ground connection on TP2 and leave off. Set HTR OK to HI. Is +5V signature
AF7A? If yes, go to step n. If no, go to step I.
l. Remove RESET jumper. Tie center pin to +5 V. Is TP2 high? If not, replace U1, U19, or
R5. If so, go to m.
Frequency should
be equal to
ratio of
F (TP5/16)
or ~ 4.8 kHz
F(U6 pin 13/16)
or 300 Hz
F(U4 pin 15/10)
or ~ 30 Hz
f(U4 pin 1/10)
or ~ 3 Hz
HP5501B
Service
If Incorrect,
faulty part is:
U6
U4 or U6
U4
U4
8-39