Repair Those Pinball Lamp Sockets

Fix Those Flicking Pinball Lamp Sockets

If you have pinball lamp sockets that flicker, dim and sometimes don’t work, this step-by-step procedure will fix them for you.

Two different Types Of Lamps

Up until recently, most pinball machines use two different types of sockets:  

  • Those round types for #44 or #47 bulbs.  These are known as miniature bayonet bulbs.
  • #555 miniature wedge shape.

Note that there are different size bulbs that use bayonet or wedge shapes.  These can be for flashers or specialty bulbs.  The fixes here also generally apply to them.

 Also, new games that have LEDs may use small circuit boards or a different type of connector that is not addressed here.

Note: Click on the photo for a larger image.

The Diode
Diode on switched lamp in a solid state machine.

All SS lamps that are controlled by the computer (except early Bally & Stern) are part of a lamp matrix and have a diode.  If the lamp never lights, it could be a bad diode that is open.

To test, remove the bulb, then put your DVM in the diode test mode and connect the leads across the diode.  One direction will read high and the other direction will read low if it is good.  If both directions read high, it is defective – replace it.  

If both directions read nearly zero, the lamp will light, but so will other lamps when only one lamp should light.  Also replace the diode.

Note that it is crucial that the band of the diode be in the same direction as it was originally.

#44 / #47 Bayonet Bulb Socket

Places where oxidation occurs
Corrosion points. Click for a larger image.
Contact points
Bulb contact points that need to be cleaned.

Most of these sockets can be restored.  As they age, corrosion occurs and corrosion (oxidation) makes a great resistor and reduces the brightness of the bulbs.  Plus, where two metal parts meet, electrical contact is sometimes lost.

Both of these points in the first photo can be fixed with solder, or solder and wire.  

In the second image, cleaning and a little mechanical adjustment will do the trick.

At points 1) and 2), the important first step is to shine them up and remove any remaining corrosion (oxidation) so that the solder will stick.  That is accomplished using an abrasive tool such as a wire brush, stone, or  carbon steel brush.  All of these are available as Dremel tools which makes this a fast and simple procedure.

Soldering The Weak Points
Shine up those spots
Shining up those spots so solder will stick.

To fix 1) and 2), pull out your Dremel and one of the abrasive tools.  I prefer the wire brush, but the carbon steel brush 443-02 will work too.  Wearing safety glasses, carefully shine up spots on both the tube that holds the bulb and where the tab comes in.

If those spots are not perfectly clean, the solder will not stick.  

Solder spot
Solder applied

Next, heat up your soldering iron.  If your iron is adjustable, turn it up high.  I use 700 F (370 C) but it could be hotter.  The solder will not stick to the bulb socket unless it is hot enough.

Pick a shiny spot on the bulb tube and heat it.  After it gets hot, apply solder until it flows on the tube.  Continue to heat where the tab comes into make a solder bridge.   It likely will not look neat, but we don’t care.  The point is to make certain that the electricity flows from the tab to the tube that holds the bulb.

Test the solder spot with a screwdriver and make certain it sticks.  It may take practice to make this a good solder connection. 

Shine up the tab.
Shine up the tab in the middle of the bottom.

Next, we are going to fix that pesky spot where the electricity comes into the point at the base of the bulb.  Once again, we have to use our abrasive tool to shine up the tab in the center.  

Once it is shined up, pull out your very hot soldering iron and apply a tab of solder on that tab.

Find a short piece of thin wire.  I keep leads from resistors specifically for this purpose.  Solder that short length to the spot of solder from the previous step.  Solder the other end to the tab where the wire comes in.

At this point, you have taken care of the weakest points on a bulb socket.

Clean The Other Bulb Contact Points
Bottom of the bulb socket
Bottom contact point.

There are two areas of the interior of the bulb that needs to be taken care of.  They are the point where the bottom of the bulb makes contact.  And the sides that connect to the tube of the bulb.  Both of these are going to be fixes using an abrasive only – no soldering.

There are two ways to do this:  1) Use a bulb socket cleaning stick, available through parts suppliers such as Marco and The Pinball Resource.  2) Or use one of our abrasive tools connected to a Dremel.

Stone Dremel tool
Using a Dremel to remove oxidation.

The bulb socket cleaning tool is the easiest.  It can be done quickly at the pinball machine without taking much apart.  But I have gotten mixed results from using these.  Try this first.  If it fixes it up, great.  If not, pull out the Dremel.

For the Dremel, use a small stone tool or the carbon steel brush and shine up that contact point.  A quick low speed spin with the center contact point shines it up and removes the corrosion.  While at it, also spin carefully around the inside of the tube.

Adjustment with needle nosed pliers
Bend those tabs or ‘ears’ inwards just a little.

The tube of the socket has two ‘ears’ where the bulb locks into place.  Those ‘ears’ can be easily bent using needle-nose pliers.  It is easy to bend them too far.  Just a small bend inwards is all that is needed.  After adjustment, insert a bulb.  The bulb should be snug.  If it is too difficult to insert the bulb, adjust with the pliers.


Pop Bumper Lamps
Pop bumper lamp sockets
#555 pop bumper lamp sockets

Pop bumper lamps that use #44/47 bayonet bulbs are terrible.  If you are determined to keep them, use the dremel tool and shine up the sides and the bottom contact.  

In the long run, replace them with a #555 style socket for pop bumpers.  The straight wire type can be used, but it is easier to use a flexible wire.

#555 Miniature Wedge shape

555 lamp socket
Crummy 555 lamp socket. Not much can be done to salvage them. Throw them out.
#44 lamps
#44/47 bayonet base lamps replacing broken #555.

In the early to mid-1980’s, some games converted the conventional bayonet bulbs to wedge shape.  Unfortunately, many of those sockets were terrible and not a whole lot can be done to fix them.  

For example, if your #555 lamps under the playfield in your Eight Ball Deluxe are giving you fits, the best to do is replace them with bayonet base #44/47.

Board containing lamps.
Board with #555 installed.

#555 sockets are frequently used on lamp circuit boards in later games.  Sometimes the lamps will flicker, dim or not light at all.  They are easy to fix. 

I usually remove the lamp boards from the playfield.  Turn off the pin,  unplug the connector and remove the few screws that hold the board to the playfield.  The cause of the problem is almost always the plug pins or the contact points where the lamp holder screws in.

Inspect both sides where the plug connects to the board. On larger board,  a bad solder connection could affect two or more lamps.   If necessary, reheat and add new solder so that it flows around the pin.  Be sure to heat the pin so that the solder sticks to it.

Solder remelted.
Solder already re-melted on this contact.

The most common problem affects only one lamp.  Usually, the bulb holder makes a ‘dimple’ of sorts on the contact area.  I find the quickest fix is to heat up the solder on the board.  Adding a small amount will make it melt easier.

Finally, if one bulb does not light at all, it could be an open diode.  Or someone replaced a diode and put it in backwards.  Test as indicated near the beginning of this page.  

If more than one lamp lights when only one should, a diode maybe shorted.