@Greg Lilly Thanks for answering Greg. Actually that's the right answer. What I did was to put a cable to replace the damaged track (no more intermittent contact) and it is working since then without problems. All lights are working now. Still thinking on getting a replacement board but no rush.

LOL, you have lot's of questions I can't really answer. Unfortunately, I'm not an electrical engineer, and likely don't have the brain power to be one. You are correct that SCRs most commonly used for converting AC current to DC current (rectification), hence the name Silicon Controlled "Rectifier". I can only assume that they are used in the lamp board because they also have the ability to handle high current and voltage, which works well with the lamp operation. Regarding the 1451 vs PIA, I can't really answer that question. But the 1451 is really only decoding a 4 bit input signal for selection of one of 16 possible lamps. Not sure if you need an PIA to do such a simple task....but I really don't know. Not sure about the 1.2V vs 0.6 V either. The diode part of the SCR is the anode and cathode legs. The voltages are read between the gate and cathode. I did look it up, and the higher voltage is read when the ground is on the gate and the positive is on the cathode. I haven't really dived into how SCRs actually work, but the gate might act as a type of "jump start" for the diode, allowing current to flow from the anode to cathode. If you, or anyone else knows, please let me know. Regarding LED flickering on SCRs...… the DC current that drives the lamps is not well regulated (it fluctuates). LEDs don't draw current when the voltage drops too much, and this causes the SCR to shut off (unlatch). It then needs a new gate signal to relatch. You can solve this issue by adding a resistor to the lamp circuit, but you have to do this to all the lamps (normally you put them on the lamp socket leads....a 1k resistor should do the trick). I think the replacement LED compatible boards have the resistors installed directly on the boards.

Thanks for the help. Adding the 1K resistor "across" the lamp socket leads from lamps positive voltage to the lamps ground? I'm confused why would adding a 1K resistor reduce and fix the LED flicker issue?Regarding LED flickering on SCRs...… the DC current that drives the lamps is not well regulated (it fluctuates). So when you put your Volt meter on the Lamps socket the DC voltage will fluctuate up and down?

@Greg Lilly But what is the advantage and benefits of using SCR to turn off/on the lamps? because Bally, Williams stop using SCRs and used FETS instead of SCR's. There must be a reasons why they stop using SCR's and used FET's. I don't see how the SCR's can send and Interrupt IRQ request to the CPU because its really hand to turn off SCR's once they are Latched. The DC voltage that goes to zero shouldn't unlatch turn OFF the SCR because the SCR will still be latched. You have to unlatch the SCR which is a resetting the SCR. You're saying that when the SCR is turned off/unlatched that it sends an Interrupt IRQ signal back to the CPU?

@Greg Lilly Yes Stern PCBs copied ballys. The Unfiltered DC is powering the SCR's but the Decoder chip output pins are tied to different SCR's gate pins to turn on/off the SCR is from the gate pin. The Unfiltered DC voltage is going to the SCR Anode pin and the cathode pin is grounded. This is before the Lamp matrix system, it causes a Decoder IC chips that controls the SCR's, later versions they used FET's. Then they used a Lamp Matrix system that uses a scanning frequency and isolation diodes on each switch and lamp. The isolation diodes will only allow the scanning pulses to flow in one direction. Without using the isolation diodes it confuses the scanning pulses. Often the isolation diodes get shorted and it confuses the CPU thinking 3 or 4 switches are closed because of only one diode that is shorted. Somehow the CPU is measuring the scanning pulses/scanning frequency and when one diode is shorted it shortens or lengths the scanning pulses so it confuses the CPU to thinking there is 3 or 4 switches that are closed which is a false positive meaning not real. I'm not sure why they used Unfiltered DC for the SCR's but the Unfiltered pulsating DC is applied to the SCR's anode pins.

@Greg Lilly yes they used Latched SCR Logic. The DC Unfiltered is going to be pulsing at 60hz, so this is going to make the SCR turn OFF at an interval frequency 60hz because of the pulsing unfiltered DC. This would cause the lamps to "flicker" from the pulsing unfiltered DC of the refreshing of the lamp ouput. The 5.4vdc that is applied to the SCR's would be pulsing DC when displayed on the oscilloscope. The Decoder chip that is driving the SCR's gate pins is turning ON the SCR to latch the SCR and the pulsating DC voltage is what is Unlatching turning OFF the SCR. For the SCR to be latched/turns on Both at the same time the Pulsating DC voltage has to be "above" the threshold on and the SCR Gate has to be turned on. This is a very short time interval for the turn on time to "occur", because once the pulsating DC is BELOW the threshold the SCR is unlatch/turned off. I would think logically this would cause lamps to flicker or the lamps won't stay turned on long because of pulsating unfiltered DC.