This discussion came up in the "project games for sale" thread about what do to when a system 1 game has a dead small transformer since small transformers (B-17921) are difficult to find.

The small transformer carries a bit more than just the high voltage for the displays:
The two transformers convert the 120 volts AC input to other voltages needed for the game. [...] The small transformer outputs the main score display voltage (60/42 volts), the computer board voltage (12 volts which ultimately ends up as +5 volts), and the score display offset/reference voltages (8 and 4 volts).
Source: http://www.pinrepair.com/sys1/

It sounds like can use Boston Pinball's LED displays:

http://www.bostonpinballcompany.com/displays.htm

According to boston pinball, the displays do not require 69vac (60vdc & 42vdc), the offset voltages, or 5vac.

The (original) MPU requires +5vdc and -12vdc at J1.

So, it sounds like you can use an arcade power supply for the +5vdc and -12vdc, and bypass the Gottlieb power supply.

Desolder the wires for the small transformer. Put ring terminals on the hot & common wires, and connect those to the power supply. Add a ground wire from the power supply ground terminal to the EMI filter's middle terminal. Get a J1 connector (09-01-6061), and connect +5vdc and -12vdc to the appropriate pins.

1: Spare
2: -12vdc
3: DC GND
4: DC GND
5: +5vdc
6: +5vdc

Since it's not common to have -12vdc on arcade power supplies (but they are readily available on ATX computer power supplies), options are limited. There are -12vdc 0.5A, 1A, and 2A Mean Well power supplies available:

https://www.digikey.com/products/en/power-supplies-external-internal-off-board/ac-dc-converters/133?k=&pkeyword=&pv1527=6&FV=fffc074a%2C2dc1d7b%2Cffe00085&mnonly=0&ColumnSort=0&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25

I'm not certain on how much draw there actually is on -12vdc.

The pinout of the 4-digit display uses +5vdc at pin 18, which is fed by the MPU (from J3) and isn't a problem.

The pinout of the 6-digit display might be problematic. It appears to take +60vdc at pin 17 from the Gottlieb power supply, and uses a 15k 1/2w resistor to drop to +5vdc. I'm not sure yet how exactly the boston pinball displays handle this. Here's two versions of the original display schematic:

pasted_image (resized).pngpasted_image (resized).png

Any thoughts?

In looking at the installation documents, it looks like the boston pinball displays are powered by a separate power supply, with a power adapter plugged into the service outlet. The 69vac line fuse is removed.

http://www.bostonpinballcompany.com/install.htm

http://www.pinrepair.com/sys1/#tools

Looks like it's involved in some way with the spider chips, some transistors, and digit/segment output lines for the displays.

Good to know

[edit]: I looked into the boards a little bit. I sent David an email about his board. And since I'm not sure if the Pascal board requires all the original voltages or not in order to boot, I dropped him an email as well.

I got confirmation that the nii-wumpf MPU only needs +5vdc.

Would you be able to use these 12v and 15v transformers along with your PI-1 X4 all-in-one board?

http://www.antekinc.com/an-0212-25va-12v-transformer/

http://www.antekinc.com/an-0215-25va-15v-transformer/

Or would the extra voltage for each circuit be too much?

Just linking to the pinwiki write-up for this thread here:

http://www.pinwiki.com/wiki/index.php?title=Gottlieb_System_1#Workaround_for_Dead_Small_Transformer

Good to hear that someone was able to do this successfully

The boston pinball displays. I linked to them in the first post.

The driver board doesn't matter since it doesn't connect to the small transfomer. Any original or aftermarket one will do.