Beast Busters gun pot replacement

KenLayton

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A friend has an SNK "Beast Busters" 3 player gun game. The gun assembly uses two 5k linear taper pots. One for the up-down and the other for the left-right movements. Seems like the ones that go bad the most are the left-right pot.

Both gun position pots are located in the bottom base of the gun unit. Remove the ten screws on the base metal covers and lift the black covers off. You might need a stubby screwdriver for the ones on the side of the cover facing the monitor glass.

The left-right pot is the one closest to the monitor glass. Removing the two 9/32" nuts, flat washers, springs, and metal spacers allow you to lift the pot & it's mounting bracket straight up and out.

The original pot is made by Cosmos/Tocos in Japan. It is advertised as being "low cost" but when I enquired wih their sales reps and distributors here in the USA, I was quoted $30 EACH! The Cosmos/Tocos part number of the original pot used in this assembly is RVQ24YN02 20FB5K. This translates the physical specifications of this pot to:

24mm diameter case
Panel mount bushing
6mm diameter shaft with flatted side
20mm from base of bushing to end of shaft
5k resistance
Linear taper

No way was my friend going to pay that much for a pot! So I was able to cross reference a replacement from Radio Shack. Part number 271-1714 (about $3 each) will work fine, but you'll need to do two things to it first in order to use it. First you cut the shaft off to the same length as the original. Next you file a flat side on the shaft same as the original. Hold both pots next to each other and turn the shafts both all the way in the same direction (clockwise or counter-clockwise just so long as they are both the same direction). Now mark the Radio Shack pot as to where the flat side needs to be filed and start filing. You only need to file about 1 mm deep. Now I want to inform you that the Radio Shack pot has open "cleanout" holes at the solder lugs and the rear case. This is so after a period of time when the pot gets dirty/scratchy inside you can spray volume control cleaner into it. The flat side of the pot is important as it fits into a "D" shaped hole in the machine's rotating gun gears. Pots with 1/4" diameter shafts will not fit. They are too big of diameter.

Here's a good tech tip: When you're hacksawing and filing the shaft, cover the pot from the base of the shaft on down over the rear cover with masking tape to keep the shavings/filings out of the pot.

I have done this on two Beast Busters gun assemblies and the Radio Shack pot works perfectly fine and at a fraction of the cost of the originals! I think these Radio shack pots will also work on Terminator 2 video game gun assemblies.

http://www.radioshack.com/product/index.jsp?productId=2102789
 
Ken,

I just wanted to say thanks for your thread posting.

I have a Beast Busters Second Nightmare cab that I'm working on and the guns were all over the place -- the pots wearing down.

I needed 5K pots for the BB2N too so I picked up a pair of these that you pointed out, cut them down, trimmed for the D shape and put them in the gun to see what happened. Worked like a charm!

I had originally contacted Tocos but they haven't replied back yet. I did take their specs and looked on Mouser.com and was going to go with a replacement that should have worked for about the same price as these parts (but without the hackery), but this was an instant gratification fix and required the use of my dremel, so a much better man-fix :)

Now I need to pick up two more and put them in the the other gun.

The old ones were so bad I had the game set to EASY. This time around, since I could actually aim, EASY was a cakewalk!

Thanks,
Jeff
 
Yeh the calibration sure seems more accurate with the new pots. The game play is sooooo much better with the new pots.
 
Those TOCOS pots are rated for 1,000,000 (turn?) cycles though.

Wouldn't the radio shack ones last not nearly as much? I've checked out mouser and a lot of the cheaper ones ($2-5) are rated for only 50,000 cycles
 
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My guns were also experiencing jumpy targeting so I tried changing the POTs with the ones recommended.

It really didn't help at all.

When Calibrating there is no issue at each extreme, the Hex positioning showing on the screen is dead stable. Whenever the gun is between any extreme position however you can see the Hex values bouncing between 2 values like crazy even when the gun is dead still.

With brand new POTs in the gun, is there any other reason this could occur? Watching the gears while turning the gun they look nice and tight and stable as well.

Is there any way to make the POTs less sensitive? Is it possible a different type of POT could be more effective? Sorry to drum up an old post but was really hoping for some insight.
 
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