Bally Feature Lamps Not Working: Lamp Driver Board Troubleshooting

On a Bally or Stern pinball machine from 1977-1985, the feature lamps (the playfield inserts and backbox lights the game switches on and off) are driven by one board: the lamp driver board. When those lamps die, stick on or flicker, most of the causes are cheap to fix, and many of them are not on the lamp board at all.

The short version: if every feature lamp is out but the general illumination works, measure TP1 on the rectifier board first. It is usually the lamp fuse, the bridge rectifier or a connector, not the lamp board. If one lamp is dead or stuck on, it is usually the bulb, the socket, the wiring or a single SCR. If a whole block of lamps misbehaves together, look at the decoder chips or the MPU connection. And if you have fitted LEDs and they flicker or glow faintly, that is a known quirk of the original board, not a fault.

BallyLA_60 replacement lamp driver board for Bally and Stern pinball machines, component side
A replacement 60-lamp driver board for Bally / Stern machines. It sits in the same position and uses the same connectors as the original AS-2518-14 / -23 boards. Photo: Pinballs Store.

Contents

How the Bally lamp driver board works

Bally split the electronics of its solid-state games across several boards. The MPU (the processor board) decides which lamps should be on. The lamp driver board does the switching. The rectifier board supplies the power. Stern used the same arrangement on its M-100 and M-200 games, so everything here applies to both brands. If the board names are new to you, our guide to pinball electronics explains how they fit together.

The original boards are the Bally AS-2518-14 and the later AS-2518-23, with an equivalent Stern board. They control up to 60 feature lamps, and the lamp wiring leaves the board on connectors J1, J2 and J3. The instructions from the MPU arrive on J4.

Three kinds of part do the work:

  • Four MC14514 decoder chips (U1-U4). The MPU sends a short binary address, and each decoder turns it into one output line. With 60 lamps and four decoders, each chip looks after a block of 15.
  • One SCR per lamp. An SCR (silicon-controlled rectifier) is an electronic switch. When the decoder triggers it, it connects that lamp to ground and the lamp lights. Bally used two types: the 2N5060 for a single lamp and the higher-current MCR106-1 where one output drives more than one lamp.
  • The lamp supply. The feature lamps run on unregulated DC of roughly 5.5-7 V from the rectifier board. The general illumination (GI) lamps, the ones that are always on, do not go through this board at all.

That last point is your first clue. If the GI is lit but no feature lamps work, the problem is somewhere on the controlled-lamp path, not the machine's main power.

Start with the lamp test

Before touching a meter, run the game's own test. On Bally machines of this era, the first press of the self-test button inside the coin door starts the lamp test: every feature lamp should flash on and off together.

Walk round the playfield and backbox while it runs, and note what you see:

Write the list down. It saves a lot of time once you have the schematics open.

All feature lamps out

This is the most common report on the forums, and it is rarely the lamp driver board. Work through the power first.

1. Measure TP1 on the rectifier board

The rectifier board has test points (TP) labelled on it. TP1 is the switched-lamp supply. Set your meter to DC volts, black probe on ground, red probe on TP1:

  • On the later rectifier boards mounted in the cabinet (AS-2518-49 and -54), expect about 6.5 V DC. Anything from 5.5 to 7.2 V is fine.
  • On the early -18 board mounted in the backbox, expect about 5.4 V DC (4.5 to 6.0 V is fine).

If TP1 reads near zero, the lamp board is not getting any power to switch, and the fault is upstream.

2. Check the lamp fuse and the bridge rectifier

The feature-lamp fuse, F1 on the rectifier board, sits before the bridge rectifier BR1 that produces this supply. Pull the fuse and test it for continuity rather than trusting how it looks. Check the correct value and type in your game's manual, and do not fit a bigger one to stop it blowing.

If the fuse is good, suspect BR1 and its solder joints. In one Pinside thread about a Bally Strikes and Spares with no feature lamps, the cause was a bridge rectifier with a bad leg. In another, on an Embryon, TP1 read 0.22 V. The owner had already replaced BR1, but the new one had been soldered badly. Tapping it brought the lamps back, and reflowing the joints properly fixed it for good. Swapping the lamp board had made no difference.

3. Check the connectors and the lamp board's own 5 V

The lamp board also needs +5 V logic power, which you can measure at TP1 on the lamp driver board itself, and good ground on J4. Old connector housings and header pins corrode and crack. Reseat them, look for burnt or loose pins, and reflow the header pins if they look dull or ringed.

One lamp dead or stuck on

A single lamp that never lights

Start at the playfield, not the board. Swap the bulb for one you know works, and check the socket for corrosion or a loose contact. Flickering sockets on old games are extremely common.

Then do the simple ground test forum techs recommend. With the game on, take a short piece of wire and briefly touch the lamp's control wire to ground (the side rail works). If the lamp lights, the bulb, socket and supply are fine, and the problem is between the socket and the lamp board: a broken wire, a bad connector pin, or the SCR for that lamp.

A lamp that is always on

A lamp that stays lit even during the lamp test usually means one of two things. Either its SCR has failed shorted, or the lamp's control wire is touching ground somewhere under the playfield. Switch off, unplug the lamp board connector that carries that lamp, and switch back on: if the lamp goes out, look at the board; if it stays on, look for pinched or damaged wiring.

Finding the right SCR

The lamp driver schematic in your manual shows which SCR (Q number) drives each lamp. Follow the wire colour from the socket back to the board. Replace like for like: a 2N5060 where the schematic shows one, an MCR106-1 where it shows one. Forum members report the 2N5064 as a workable modern substitute for the 2N5060. Changing an SCR is a normal, three-leg soldering job, well within reach if you have repaired a board before.

A block of lamps wrong, or lamps going crazy

When lamps fail in a group rather than one at a time, think about the parts they share.

  • A block of lamps out or wrong together. Each MC14514 decoder handles a block of lamps. A failed decoder, or a bad socket under it, takes its whole block with it. Faulty MC14514s are one of the typical defects listed by people who repair these boards.
  • Lamps flickering randomly, or all lamps behaving erratically. The data comes from the MPU through J4. A poor connection there, or a fault on the MPU side, makes the lamp board do strange things even when it is healthy. In one solved Pinside case, feature lamps went "like a Christmas tree" and then died completely. The fix turned out to be on the repaired MPU: a problem around the 555 timer and, finally, the socket of the U10 chip, which was replaced.

So before condemning the lamp board, check J4 and its wiring back to the MPU. If the MPU is also showing trouble at power-on, our guide to Bally MPU LED flashes is the next place to look.

LEDs flickering or ghosting

If the trouble started after you fitted LED bulbs, it is probably not a fault at all. The SCRs on the original board were designed around incandescent bulbs, which draw far more current. An SCR needs a minimum current flowing through it to switch cleanly, and an LED may not draw enough. The result is flickering, faint glowing, or LEDs that will not light properly.

There are two well-trodden fixes:

  • Add a load resistor at the problem sockets. Forum members solved flicker with a 470-ohm resistor across the lamp socket. It is cheap, but on some games you need it on several lamps.
  • Use a lamp driver designed for LEDs. Newer boards replace the SCRs with transistor-style outputs that do not care how little current the lamp draws.

Some owners simply keep incandescent bulbs in the few awkward positions. If you are planning a full conversion, our complete guide to converting a pinball machine to LED covers bulb types and colours.

When replacing the lamp board makes sense

Most lamp faults are cheap fixes: a fuse, a bridge rectifier, a connector, a bulb, an SCR. Do those first. Replacement starts to make sense when:

  • several SCRs and decoders have been changed and faults keep coming back;
  • the board has corroded traces, lifted pads or damage from earlier repairs;
  • you want to run LEDs everywhere without adding resistors at each socket.

If you get there, the BallyLA_60 is a plug-and-play 60-lamp driver for Bally and Stern machines of 1977-1985. It takes the place of the AS-2518-14 / -23, uses protected MOSFET outputs that work steadily with LEDs, and has built-in test buttons to check each lamp. We test boards before they ship and support them afterwards. For fitting, see our plug-and-play installation guide.

One honest caveat: a new lamp board will not fix a dead TP1, a blown fuse or a bad J4 connection. Measure first, then decide.

FAQ

Why are my Bally feature lamps not working when the GI lights are on?

The GI does not use the lamp driver board or its supply. Measure TP1 on the rectifier board: if it is near zero, check fuse F1, bridge rectifier BR1 and their solder joints before suspecting the lamp board.

What voltage should TP1 read on a Bally rectifier board?

About 6.5 V DC on the cabinet-mounted -49 and -54 boards (5.5 to 7.2 V is fine), and about 5.4 V DC on the early backbox -18 board (4.5 to 6.0 V is fine).

Why is one lamp stuck on in my Bally pinball?

Usually a shorted SCR on the lamp driver board, or the lamp's control wire touching ground. With the power off, unplug the lamp board connector, then power up: if the lamp goes out, it is the board; if not, it is the wiring.

Do LEDs work with the original Bally lamp driver board?

Often with problems. The SCRs need more current than many LEDs draw, which causes flicker or ghosting. A 470-ohm resistor across the socket, or an LED-friendly lamp driver board, fixes it.

Which SCRs are on the Bally lamp driver board?

The 2N5060 for single lamps and the MCR106-1 where one output drives more than one lamp. The schematic shows which is which for each Q number.

Is the Stern lamp driver board the same as Bally's?

Stern's M-100 and M-200 era games use an equivalent lamp driver, and replacement boards are sold to fit both. The same diagnosis applies.

Sources

Not sure whether it is the lamp board, the rectifier board or the MPU? Tell us your machine and what the lamp test shows. Our technical support is free, before and after purchase, including when the answer is a cheap fix you can do yourself.

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