Bench test of coil buffers Z6 and Z7

Steps

• Z6 (7417) is just above J5 and Z7 to its right; U4 drives them and they drive Q25-Q32.
• Power the board and clip a lead to +5 V at the top lead of C16.
• Touch each input and probe its output: Z6 pins 1/2, 3/4, 5/6, 9/8, 11/10, 13/12, and Z7 pins 1/2 and 3/4.
• An output that does not follow its input means a bad 7417.

Systems

• Gottlieb System 1

Related tips

• Ni-Wumpf board coil buffer chips
• Powering a System 1 CPU board on the bench
• Using an LED to see a bench CPU boot
• Testing CPU input buffers Z29 and Z27
• Firing coils from CPU buffers Z6 and Z7
• Spare chips for System 1 boards
• The six Rockwell "spider" chips on the CPU board
• Which spider chips fail and why

Source: Gottlieb System 1 Pinball Repair from 1977 to 1980, Clay Harrell (pinrepair.com)