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 and generally do not have these types of problems.
Note: Click on the photo for a larger image.
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. In the above photos, the wire is connected to the lower tab. The band of the diode goes towards the tab with the wire.
#44 / #47 Bayonet Bulb Socket
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.
Some Differences in Construction
On the bottom of the bulb socket (#2 above), there might be an ‘open flange’ with a hole in the middle of it. Or it might be a closed tab or button. It does not matter as the fix is the same.
Also, some the sockets might have a tab connected to the barrel (#3 above), or that barrel might not have a tab and the wire is connected to the bracket (#2 picture above). It does not matter as this fix is also the same.
Some sockets might have a third tab. The wire comes into that third tab, then a diode is connected to bottom tab (#2 picture above). This is a crucial difference as the diode must be left in the circuit. The ‘fix’ wire must be made from the diode non-banded side (not the wire / diode banded side) to the lamp button.
Soldering The Weak Points
Pull out your Dremel and one of the abrasive tools. We 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.
Next, heat up your soldering iron. If your iron is adjustable, turn it up high. We 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.
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 stiff wire. We keep leads from resistors specifically for this purpose. Remove the bulb. 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. After the socket has cooled, replace the bulb. Using a stiff wire here has the added benefit of increasing the ‘spring’ pressure on the base of the bulb.
It is possible to use stranded wire for this connection, but that will not increase the pressure on the bulb.
Some move the wire connection from the tab to the base of the bulb, but this is not recommenced.
At this point, you have taken care of the weakest points on a bulb socket.
Clean The Other Bulb Contact Points
There are two areas of the interior of the bulb that needs to be taken care of (#3 & #4 in the photo). 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.
The bulb socket cleaning stick is the easiest. It can be done quickly at the pinball machine without taking much apart. But we have gotten mixed results from using these. Try bulb cleaning stick 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.
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 lamps that use #44/47 bayonet bulbs have terrible sockets. If you are determined to keep them, use the dremel tool and shine up the sides and the bottom contact.
For reliability, 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. The downside of the flexible wire socket is that it stands higher and the bulb may not fit in with the pop bumper cover on. If using LEDs, use the shorter bulbs that are readily available.
#555 Miniature Wedge shape
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.
#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.
The most common problem affects only one lamp. Usually, the bulb holder makes a ‘dimple’ of sorts on the contact area. We 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.
Comments, including suggestions, improvements, errors, etc. are welcome (see below).
If you have a specific question about your game that does not directly apply to fixing lamps, please see our FAQ section.