With the coin door open:
Pressing the Diagnostic button on a properly functioning System 7 MPU will cause the 7 segment display to flash a zero and then go blank. System 7 diagnostics are a bit more useful than prior Williams game systems but are still not 100% trustworthy. If the MPU built-in-test software detects a problem with the game hardware, the 7 segment display will remain on with an error code displayed. Possible error codes are:
0 - and then goes out...all tests passed
1 - IC13 RAM or IC20 ROM failed
2 - IC16 RAM failure
3 - IC17 ROM failure
4 - IC17 ROM failure (duplicated test...yes)
5 - IC20 ROM failure or the coin door was closed or memory protect fault
6 - IC14 Game ROM failure
7 - IC26 Game ROM failure
8 - IC19 (5101) RAM failure or the coin door was closed or memory protect fault
9 - IC19 (5101 again) RAM failure or the coin door was closed or memory protect fault.
Tests 1,2,8,9 are not very reliable - lots of false positives - but if you do get a failure here you'll need to replace the related chip.
You can try it before and after the crash and see what you get. If the system truly is crashed you wont get any results at all AFTER the crash.
Note that running these built-in diagnostics the lamps and the displays will go out.
Let me know what you find