Diagraph PA/4000, Service Manual, Page: 153 / 213

Technician’s Guide 2-9
J8
A
B
C
D E G
H
F
Figure 2-2
Starting clockwise:
U13 and U12 are the RS-232C and RS-422 line drivers. In the event that these chips may be
damaged by high voltage spikes or misuse, either chip may be replaced to return the
PA/4000 to normal communications with the host device. The outputs of these two chips
connect to other circuitry in a way that the desired interface is enabled by the connection of
wires to the pins on J2.
U2 , the 74HC245 in the upper left hand corner, buffers the settings of SW1 on the back of
the PA/4000 from the control board data buss. If the self test patterns (see the Prodigy Plus
Operator's Manual) indicate that the switches do not change when you have physically
flipped the switches, replace this chip first. Replace the switch bank later if necessary.
U3 is the microprocessor. If the board has voltage, and nothing seems to run, you may try
replacing U3.
U4 through U6 and U30 are the ROM and RAM that are checked during power up and by
the self test (see the Prodigy Plus Operator's Manual). If you encounter a printed error
statement, replace the indicated chip.
U21 and U22 are the buffer chips between the control board and the applicator board. If the
PA/4000 was subjected to very high voltage discharges, these I/O chip could be affected.
All the TTL level data is buffered by these chips.
U15 through U18, U23, and U27 are the IC's that most directly affect the shifting and
burning of dots to and at the printhead. These components are not likely to be damaged
but replacing the complete set of six is most likely more efficient than trying to hit them one
at a time.