FYI:
when it comes to measuring voltages on test points, while it's a good (quick) indicator of a voltage being present/missing/correct, you should always measure the voltages on the IC pins themselves, as the test point voltages are often always 'before' all the (faulting) components down the line...
Of course monitoring the 5v on any form of reset/monitoring chip is a must, and any capacitors around the reset circuitry must be changed too.
Also note that while a reset circuit/chip might have a VERY stable 5v on it, it will often be a faulting capacitor associated with that circuitry that's upsetting the reset signal.
Another thing to check (that many many many people overlook) is to not only measure your DC volts (5v, 12v, -12v etc), but also set your multimeter to AC volts, and re-measure those voltages again.
If *any* of the voltage rails has more than say 100mV (milli-volts) of AC on it then you need to look back further at replacing power supply filter capacitors & regulators etc.
( if you have several 'volts' of AC, then you definately have filter-cap issues ).
I see this same issue time & time again on all kinds of equipment outside the pinball genre, and the golden rule is always ".....Get the power supply working correctly FIRST and most faults go away"
No use trying to repair a fault elsewhere if the power supply wont let it work correctly ;-)
Additionally, for boards that reset often, you should see some sort of LED activity on the mainboard each time it resets.....(remember which LEDs are doing what, at bootup, especially if there's an actual rest LED).
Now unplug all external cabling looms to solenoids & switches and other boards (just leave power connected to mainboard) and powerup.
Does it still reset? (watching the LEDs for reset activity that you previously 'remembered'), if YES, then fault is definately on main board.
if it doesn't reset anymore, then the reset fault is being caused by another board, or external wiring on switch/solenoid matrix.
You would then plug in other boards/ribbon cables 1-by-1 and reboot each time, seeing if the reset problem has been re-introduced.....then after all boards are attached, start adding the solenoid loom and switch loom...
Somewhere thru that above 'replugging stage' the reset problem will return and you'll know exactly which board or loom is causing it.....
MM
