The transformers used in the -54 games can put out up to like 8vdc for feature lamps once rectified. Lamps are nice and bright but they burn out quick. Common op hack was to use an extra bridge bolted to the metal mount bracket to get a extra V-Drop across the diodes in the bridge making the lamps run cooler and last longer.

I left this hack in my black pyramid because the feature lamp voltage, specially when low load LEDs are used, was like 8vdc without it. Certain LEDs lamps where getting hot enough to fail and melt.

this is the extra bridge circuit which drops 0.8vdc-1.2vdc from the feature lamp bus. Burns it off as heat into the metal bracket bridge is mounted to.
Fullwave-Bridge-Rectifier (resized).png

TP1 = 7.7vdc is probably why the hack is in there. Pretty typical for some of these transformers to put out that much voltage. Maybe they where expecting locations to have low line voltage.

Whether or not it makes the LEDs burn depends on the current limiting resistors inside the LED lamp and probably varies somewhat brand to brand and even color to color. In my xp some SMT type where fine, but got warm, but other types of LEDs that stayed on most of the time got so hot they started to melt.

TP2 probably is reading wrong because of no load/filter cap but check the fuse and the 1n4004 diodes. Some multimeters fail to get a reading for whatever reason. Sticking a resistor in series with positive lead helped on one DMM i was fiddling with. When the driver board is connected it should come up to 230v.

I some how read 245v as 24v or something. It is a little but fine.

its not the chassis mount as a replacement, although that happens too. In the OP looks like they wire up a 2nd bridge to get more voltage drop of the bus voltage across the 2nd bridge. Kind of hacky way to drop 0.8-1.2vdc but works.

I kind of think one or two distributors did this to all the games they sold. The hack is pretty standard in application of how they do it. I got a bunch of -54 boards over the years with that hack done.

Eiko and the unbranded Chinese 100 packs currently manufactured 555 bulbs seem to burn out quick compared to some old ones. In one year of minimal home use a Dracula had burned out bulbs and many silvered =/.

I'm sold on the warm white 5050 smd led lamps with a frosted dome. They light up fine even down to ~5v.