Another low +5v power issue, but I think different than others I've seen posted here and in the STTNG thread. Based on my diagnosis so far, I'm thinking something on the CPU board may be drawing down the 5v, see if you agree or disagree. About to pull the CPU board to install updated ROMs and a coin cell holder to replace remote battery holder, decided to also remove the Kahr board (installed a year ago or so, was preparing for a party when a reset happened) and analyze the +5v situation for a proper fix.
Stock TZ. Z connector removed properly a couple of years ago. No mods other than gumball flashers on playfield door panel. TZ has been in my home for over 20 years and sees very little use, so little "on" time. Mounting screws on driver board are snug. 124v at TZ's service outlet. C5 was replaced some time many years ago, not sure about BR2. Nothing else is powered up on TZ's branch circuit. Tests were run with a game started, but not actively being played.
Before removing Kahr board, 5.05v at Game ROM pin 32, 4.84v at TP2 on driver board.
After removing Kahr board, 4.80v at Game ROM pin 32, 4.81v at TP2 on driver board. Below 4.92v, so risky.
After reseating J101 4.84v at TP2, gain of only 0.03v.
After reseating J114, 4.81v at Game ROM pin 32, gain of only 0.01v.
After reseating plugs at transformer, no change in TP2 voltage.
Remove J114, J116, J117 and J118, 4.97v at TP2, gain of 0.13v. Seems significant.
Replace J114, TP2 drops back to 4.85v.
Replace J116, no change in TP2 voltage.
Replace J117, no change in TP2 voltage.
Replace J118, no change in TP2 voltage.
With all connectors in place, tested BR2 and associated cap as per Pinwiki instructions using a test lead clipped onto the top left lead (positive) of BR2. DC volts = 10.07, AC volts = 237mv.
Did not examine the Thermistor, haven't pulled any of the boards yet (so haven't checked for poor solder joints) but the boards look unhacked.
The standout item to me is the drop in +5v reading at TP2 from 4.97v with J114 disconnected to 4.85v with J114 reconnected. So, something on the CPU board is pulling down the +5v?
I do have a PSU5 on hand so I could easily replace the LM323K when I have the driver board out for inspection, and was thinking of doing that anyway to reduce current draw / heat.
How would you proceed next?