HELP: LED won't turn off after converting pushbutton bulbs from incandescent

polarwong

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HELP: LED won't turn off after converting pushbutton bulbs from incandescent

Hello everyone!

I recently started working on a whole bunch of Medalist dart machine which were either returned from locations or stored at a warehouse for more than 5 years.

One of the first things I noticed was many of the bulbs in the buttons are burned out. Those were old 12v T10 Incandescent bulbs, so naturally I proceeded to order LED replacements for those bulbs from the "trusty" site Taobao from China (kinda like Aliexpress, in fact the same owner but Taobao is more B2C oriented, and they sell really cheap stuff! LED T10 replacements can be as cheap as US$0.02/pc, microswitch/button/LED assembly for US$0.5/pc, more on Taobao later).

The LED lights arrived, I installed them, they were great looking. I was all good until I discover something odd - they are not blinking as they should.

I went into the test menu and tested them - the LEDs are just dimming a tiny bit rather than turning off.

I went ahead and tested the voltage, they read:
12V when "On"
around 10V when "Off"

Apparently those LEDs can be powered by just 10V, or even lower and the IO Board is keeping the voltage up. It's to keep the bulbs "warm" I assume (extends the bulbs' life).

The LEDs are powered by an IO board which is then connected to the main computer. The IO Board is propriety, I should not mod the board as they will later be shipped to other places and maintained by other technicians. There is a 12pin connector for switches and bulbs:
Pin 1-5: Button 1-5 Signal
Pin 6: Button Ground
Pin 7-11: Button bulbs Ground*
Pin 12: Shared +12v for bulbs*
*Cannot remember is it shared ground or shared 12v

In such case, is there any ways to make the LED bulb work? I am thinking of adding an "limiter" board between the IO board and the cable.

I am open to any feasible solution, as long as it works and is reversible.

Sorry for the broken English, greeting from Hong Kong. Let me know if my English was too incomprehensible.

Thank for all your help in advance!
 
Are these LED bulbs designed for 12 volts?

The problem you describe is called "ghosting" and happens all the time in pinball machines. You can do one of two things: Buy "non-ghosting" LED bulbs (more expensive than regular LED bulbs) or you can install a load resistor across each bulb socket. Typically in pinball machines (6 volt) they use 470 ohm 1/4 watt resistors as the load resistor soldered to each lamp socket to eliminate ghosting.
 
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