(Topic ID: 207553)

Gottlieb Sys1: Replace dead small transformer with LED displays & power supply

By ForceFlow

1 year ago

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  • 14 posts
  • 6 Pinsiders participating
  • Latest reply 7 months ago by northvibe
  • Topic is favorited by 9 Pinsiders


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#1 1 year ago

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:


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
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:


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?

#2 1 year ago

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.


#3 1 year ago

What is the -12v used for?

#4 1 year ago

Trying to zoom in on the BPC display boards, and they look like they have GND, 5V and 4V silk screened on their J2 and maybe the same on J3?

Quoted from zacaj:

What is the -12v used for?

The -12V is for the original MPU board - something about the Rockwell chips needing this voltage.

#5 1 year ago
Quoted from zacaj:

What is the -12v used for?


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

#6 1 year ago

Technically, the 11660 (Rockwell PPS-4/2) runs on 17VDC. But, by using somewhat standard power supply inputs (+5 and -12) it uses various components to interface with 5V logic.

#7 1 year ago

From what I can tell, both the NiWumpf and Pascal Janin PI-1(X4) boards only use +5V so the -12 is not necessary if you have already dumped your original Gottlieb MPU board.

#8 1 year ago
Quoted from CactusJack:

From what I can tell, both the NiWumpf and Pascal Janin PI-1(X4) boards only use +5V so the -12 is not necessary if you have already dumped your original Gottlieb MPU board.

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.

#9 1 year ago

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

#10 1 year ago

Also the LISY1. More on that later...

#11 1 year ago

hello everyone

my PI-1 board uses +5V only.

my all-in-one PI-1 X4 board uses 11VAC and 14VAC taps from the small transformer, but not the 69VAC.
therefore it could still run on a damaged transformer whose 69VAC tap often blows due to reverse insertion of A2P1 connector on the original GTB power supply..

in addition to this, my all-in-one PI-1 X4 board generates enough current on the 12VDC output available at the screw-clamp connector J1, so that it can directly power Boston Pinball's excellent displays without need for an additional power supply block.

see the attached picture: direct power to the displays or to the dimmer provided with each displays kit.

Connect_PI1X4_eng_s (resized).jpg

#12 1 year ago
Quoted from Pascal_J:

my all-in-one PI-1 X4 board uses 11VAC and 14VAC taps from the small transformer

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



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

8 months later
1 month later
#14 7 months ago

I’m gonna bump this. Has anyone had to do what force flow is describing to skip the small transformer?

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