The CPU LED flashes seven times and then goes out without the game booting; sometimes it retries, or lights a few playfield lamps and then crashes. The solenoid board is known good and the game works with a replacement CPU.

CPU gives all seven flashes, then crashes or won't boot: bad socket at U10

Cause: A bad chip socket at U10 on the CPU board. Members note that after the seventh flash the PIAs start driving the lamps and displays, so a marginal connection or a weak 5 V or 12 V supply often shows up exactly at that point.

Checks

• Look for corrosion under the sockets (especially near the battery area) and check the traces above the battery for continuity.
• Measure 5 V and 12 V at the CPU test points while it boots; the original reset circuit needs good 12 V.
• Inspect and reseat the socketed chips, and replace any socket with poor contact.

Fix

• Replace the faulty U10 socket and reseat the chip.

Systems

• Bally MPU AS-2518-35

Games

• Flash Gordon

Related tips

• CPU flickers then gives three flashes: bad PIA at U10
• DIP switch changes seem to do nothing: count the switch numbers correctly
• Intermittent or dead MPU from old closed-frame sockets
• MPU stops before the 7th LED flash (no 43 V)
• Seven flashes but no attract mode
• Six flashes only: 43 V, U10 or U14
• Intermittent MPU faults from old closed-frame chip sockets
• Game locks up entering bookkeeping after a battery change

Source: Pinball Repair help group!! (Facebook group)