Digital Signature Analysis (Dsa); Display Problems; Line Generators - HP 8560A Service Manual

Digital Signature Analysis (DSA)

Digital Signature Analysis (DSA) places microprocessor, A2U1, in a simplified known
state. This simplified state consists of placing a one-word instruction, MOVE QUICK,
(0111 XX10XXXX XXXO) on the data bus. The microprocessor cycles through its address
range continually reading the instruction. Perform the following DSA procedure to test the
operation of microprocessor, A2Ul:
1. Set the HP 8560A's LINE switch off.
2. Move the DSA jumper (located in the middle of the A2 assembly) from connecting E6 and
E7 to connecting E5 and E6.
3. Remove jumper A2El. A2El is a 16 pin dual-in-line package located in the middle of the
A2 Assembly. Set the HP 8560A's LINE switch on.
4. Use an oscilloscope to confirm that address lines, address strobe, and chip selects are
toggling at proper levels.
5. Use an oscilloscope to check the address line sequencing. The signal on each line (starting
with Al and ending with A23) should be one-half the frequency of the previous line.
6. If step 4 reveals problems, microprocessor A2Ul is probably faulty.
7. Set the HP 8560A's LINE switch off. Replace jumper A2El. Move the DSA jumper from
connecting E5 and E6 to connecting E6 and E7.

Display Problems

Line Generators

See function blocks D and I of A2 Controller Schematic Diagram (sheet 1 of 4) in the
Component-Level Information binder.
The line generators convert the digital display information to an analog output suitable to
drive the Al7 CRT Driver assembly. These circuits change the digital words into vectors,
or lines, which move the beam of the CRT. The vectors are each 6 ~LS long (width of the
INTEGRATE pulse) followed by a 1 ~-LS SAMPLE pulse. When characters of text are being
drawn, the vectors are 3 ps long.
1. On the HP 8560A press (PRESET).
third soft key.
3. Set an oscilloscope to the following settings:
Amplitude scale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 V/div
Sweep time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 ms/div
Triggering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..External
4. Externally trigger the oscilloscope off the signal at A2U207 pin 8 (LBRIGHT).
9-4 Controller Section
MORE CRT
ADJ PATTERN. If the display is blank, press the