If you have an unrestored Space Encounters machine, the strobe unit in your Space Encounters probably doesn't work correctly. The strobe bulb has long since burnt out, as has the red light bulb. Electronics in the board itself may have also died over the years. This strobe unit adds cool, unique effects to the game, so here's some tips on getting it going again.
Replacing the Big Red Bulb
The 200w red incandescent bulb should light during attract and game mode every time an enemy is shot. It illuminates both the game marquee and the spaceship scenery around the screen.
Unfortunately, these 200 watt red incandescent bulbs are impossible to come by these days. There is a light bulb store in Portland, Oregon called Sunlan Lighting that carries every kind of bulb you can think of and more. They used to be able to order them (someone used them in caring for their chickens) but can't get them anymore from any of their suppliers.
200 watt white bulbs are still generally available and I purchased a couple thinking it might be possible to paint them with a heat-resistant red paint. In a pinch, I also considered using a white bulb and wrapping it in a red theater gel to make it appear red.
As for LED bulbs, Bluex makes a 120 watt equivalent Red LED bulb that might be a good replacement. View at Amazon
In 2007, I purchased a 100 watt red incandescent bulb at Sunlan and have been using it as a suitable replacement. Note that while not the original 200 watt, this is significantly brighter than the far more common 40w party bulbs. A 200w incandescent bulb will produce approximately 3700-3880 lumens while 100w bulb is about 1600 lumens.
Replacing other components on the board
If, after replacing the bulb, your red light still doesn't light, look into replacing one or both of the MOC3011 amps with NTE3047 (datasheet). Replacing this amp got one of my units working again. I also bought a replacement for the Triax SC141D (crosses to NTE5608 - datasheet), but didn't need to use it. As of 2024 both of these parts are still available.
Strobe Light Repair
The strobe bulb should flash several times in game mode each time an enemy is shot. Bally/Midway used the same strobe unit in their pinball, Flash Gordon, with some parts left unpopulated. Pinballmagic.com used to sell a replacement flashbulb and replacement reflector for $10. The unit worked well and came with installation instructions, but they look to be no longer in business.
Your reflector may still be good and you just need a new strobe tube. In 2008 I bought two different strobe bulbs from The Electric Goldmine, a 10w for $1.00 and a 12w for $1.25. I installed one and didn't get a flash, but I moved on to other projects and didn't get a chance to dig into what might be the problem. They have a new website and the old links and part numbers don't work. They are currently selling this strobe bulb for $1.25 which could be one of the bulbs I bought. I can't yet confirm it will work.
Based on the 2022 video below by Deep 6 Arcade, this part (F1P-C-04-05-00) looked promising, but is also now discontinued:
Marco Part# 24-8835 Attack From Mars (Bally) Xenon Lamp
YouTube video from 2022 by Deep 6 Arcade on repairing the Flash Gordon strobe:
This Flash Gordon Strobe Forum Discussion from 2016 has some useful information.