Check the feature lamp 10 amp fast blow fuse at F1 on the rectifier board.

If you measure about 7.8V AC across the "AC" pins of bridge BR1 and 0.7V DC across the "+/-" pins of BR1 then the BR1 bridge rectifier is faulty.

That is 5V logic power for the decoder chips on the lamp driver board, it's not related to power for the feature lamps.

How much voltage do you measure on the braid wire that connects to the base of every feature lamp socket? it should be around 6V DC.

4.2V sounds unusual. Where are you connecting the black multi-meter to ground? Connect it to the ground braid strap running across the lower left side of the cabinet when measuring the feature lamp socket voltage.

What happens if you connect ground to the tip lug of a feature lamp socket? Does the lamp illuminate?

Lamp_Socket_Controlled.png

I recently had this exact same problem on my Eight Ball. And of course, it happened during a tournament.
After much schematics research and testing, here's what I did to fix it:

Check for cold solder connection break on BR1.
Reflow J1-1 and J1-8 on rectifier board.
Repin connectors J1-1, J1-2 and J1-8 on the rectifier board.

My tilt was not registering, and the credit light button was not working, also. For that:
Repin J3-12(tilt) and J3-14(credit button) on the MPU.

It's been working like a champ since.
My poor connections on J1 at the rectifier board (and wiggling of that connector) had ended up causing a BR1 connection to come apart.
So, verify that your BR1 is solid. Then your problem, I'd be willing to bet, is due to these connectors.

Chears
Enaud

The lights you tested this on are 100% working lamps and not blown?

The low feature lamp voltage suggests a possible rectifier board J1 connection issue as Enaud suggested.
Post some clear pictures of the rectifier board J1 connector - let's see if it has suffered heat stress.
BTW are the backglass feature lamps working?

You have 9 pins in your j1 connector and 8 pins on your board. The leftmost wire isn't connected to anything.
At least that's how it looks in the one pic. I'd double check that, and get rid of the 9th 'rib' on the connector so it doesn't cause confusion.

Make sure all the pins are going into the correct circuits.

Pinslot - You asked about how to measure voltage at the pins - my method is this: Black lead to ground - use alligator clips on probe and ground braid to ensure a good connection. Put one end of another alligator clip on red probe, and the other end attach a leg of any resistor you have lying around. Insert the same leg into the back of the connector at the pin you want to measure. that way you are reading the voltage that the pin is getting.

What exactly were you working on the game right before the problem occurred?
Are you using LEDs or old incandescent lamps?
When you wiggle the blue wire at J1-7 do the feature lamps come on?

You need to measure the voltage going into the BR1 bridge and the voltage coming out.
The problem is the big heatsink covering the bridges makes this difficult.

You can try and measure the feature lamp AC voltage at the transformer if you are comfortable doing so. Set your multi-meter to AC voltage. Put one meter probe on transformer lug "13" the other meter probe on transformer lug "14". What is the reading?

For everyone else's reference below, is a picture of the PinLED rectifier board per their website.

RectifierBoard_PinLED.jpg

Ok, just checking

How about the other question: is it running LEDs or incandescents?

From memory test point TP1 should measure around 6 volts. You measured 5 volts which is a little low considering no load and 4.2 volts on the playfield. Even if the playfield feature lamps had 4.2 volts, the feature lamps should still illuminate though they will be dimmer.

You mentioned BR1 had a cold solder joint when you bought the rectifier board. Have you reinspected the soldering on the bridge incase other joints have since failed?

BTW didn't I send you a ROM update a few years ago that speeds up the bonus countdown?

Pinslot - put the probe on the other side of the resistor - you are just using the wire lead of the resistor as something to touch the back of the pin so you can read the voltage with the connector attached to the board.

Also, it looks like a few of the wires attached to your rectifier board have poor solder joints - for example, the third one on the top has loose wire strands - this limits current (At a minimum).

You didn't. Your DC + output is correct. The two AC terminals need to be measured with your meter on AC and the leads one on each of those terminals.

The output being correct tells me that your input is OK. Your loss of voltage is farther down , a trace, connector, or some other wiring.

I'm not sure if it's artifacts on your picture but the soldering on the lower yellow circled BR1 AC terminal doesn't look right. It kind of looks like the joint is cracked but hard to tell.

Following on from what others have said, to test the bridge, set your multi-meter to AC voltage mode.
Put one meter probe (doesn't matter which one) on either AC bridge BR1 terminal and the other meter probe on the other AC bridge BR1 terminal. You should measure 7.8VAC to 8.3VAC

Next change the multi-meter to DC voltage mode.
Put the black meter probe on the Neg "-" terminal of the bridge (which is connected to ground) and put the red meter probe on the Pos "+" terminal of the bridge. You should measure around 5.6VDC to 6.2VDC.

The Pos "+" terminal of the BR1 bridge goes to connector J1 pin 7. You should also measure 5.6VDC to 6.2VDC at that pin. J1 pin 7 is where the playfield gets power for the feature lamps.

Where you have soldered the Pos terminal of the bridge, I suspect maybe the board trace on the other side that goes to the connectors is not making contact with the bridge pin and could be where the connection is being lost. Just a guess.

Be very careful with the rectifier board being dismounted that is does not short to the transformer or anything else.

RectifierBoard_PinLED_rear.jpg

What quench said some of the connections look like they need to be resoldered.

Can you clarify exactly where you had the meter probes for this test?

Since BR1 Pos "+" leg is a direct connection to J1 pin 7, the measurement *between* these two pins should be zero volts.

So black meter probe on the Neg "-" BR1 leg and red meter probe on J1 pin 7 should measure 5.99V DC, same reading as when the red meter probe was on the Pos "+" leg.

So this time with the black meter probe on the Neg "-" leg of BR1 and the red meter probe on J1 pin 7 you get 0.6V DC? If yes, then both of these quoted readings tell me you have an open circuit from the Pos "+" leg of BR1 to J1 pin 7.

My guess is the open circuit is on the other (front) side of the circuit board where you soldered the Pos "+" leg. There is a trace from there to J1 pin 7 then down to J3 pin 6. Repairing this might be a challenge if you're not comfortable soldering or don't have the right desoldering equipment.

If I may be perfectly honest, that trace is too narrow for the current draw of the feature lamp circuit. Next time you need a rectifier board consider buying from elsewhere. That trace might be ok for LEDs but not incandescents.

RectifierBoard_PinLED_FeatureLampTrace1.png

Usually I say go for original boards, but in this case, almost all the repros are better. I use the nvram.weebly one, since I can get it as a kit. Might be expensive for you to get there so maybe go with one made in the EU?

Alltek

Yes, try it. Make sure not to strip the jumper wire ends too much to prevent bare wires touching things they shouldn't and try to make solid solder joints.

I have Alltec boards in my Star Trek and have had no issues using 47 bulbs

You must follow how your game is wired because you're operating on 220V mains supply (being in Gernamy?)

Third Coasts recommendation is for the US who operate on 115/120V mains supply. Don't wire it this way.

Follow the schematics. Thick Red wire to lug 1 on the transformer. Thick yellow wire to lug 12 of the transformer. Transformer lug 3 should be connected (jumpered) to lug 5.

Transformer_220V.png

Heh, it's in all the Bally manuals of that time. But for some strange reason that page is missing from the Star Trek manual on IPDB.
It's on page 1 titled "INSTALLATION". For example you can see it in Playboy, Supersonic and other manuals of that era.

Pull each wire out of the female housings and verify it isn't broken. You cannot tell if a terminal is broken by inspecting the outside. They may look fine like they are hooked in place on the housing, but may not be and even hooked may be busted on the inside making either no or flaky contact. I've been bitten by this.