COPYRIGHT © 1995 MERIT INDUSTRIES, INC.
TSB4
Technical Service Bulletin
1
7HFKQLFDO6HUYLFH%XOOHWLQ
06/7/95
merit industries, inc.
Problem:
Failure of video sync driver chip.
Games affected:
Some games with CRT-250 or CRT-260 CPU boards.
Symptoms:
Unstable picture due to loss of vertical or horizontal sync.
Cause:
Sync driver chip may be damaged by ESD from monitor.
Solution:
If game exhibits this problem, replace U8 (7406) (or U23
for the CRT-250 board) and add two transient suppressor
diodes to the to the sync outputs for protection. To order
the diodes, call Merit Customer Service at 1-800-445-
9353 and ask for (2) SC2111 Zener diodes.
Instructions
1.
Open the rear door and slide the CPU board into its service position.
2.
Disconnect any harnesses, cables and/or ground straps connected to the
CPU board and remove the board from the cabinet. Be sure to remember
the orientation of the board so you can put it back the same way.
3.
Locate J3, the 65-position connector on the CPU board. Turn the board
solder-side up, and locate the pins for J3.
4.
Following the diagram in Figure 1, solder the cathode end of the supplied
voltage-suppression diodes, to Pin 4 and Pin 5 of J3,
on the solder side
of the CPU board.
5.
Solder the other end (anode end), of the diode attached to Pin 4, to the
ground patch to the right of Pin 1. You may want to scratch off some of
the green coating covering the ground patch, to make a better connection.
Solder the anode end of the Pin 5 diode to the ground patch(es) to the left
of Pin 6 or to Pins 7, 8 or 9. Ground patches and pins can be seen in
Figures 1 and 3.
6.
Remove the existing video sync driver chip by carefully inserting a
screwdriver underneath it and gently prying it up. Install the new chip in its
place. Chip locations can be seen in Figures 2 and 4.
7.
Place the CPU board back on the PC shelf and reattach all harnesses.
8.
Put the shelf back into the cabinet and you’re ready to go.