How did you test the voltage of the pop bumpers when firing? And were you measuring DC or AC volts?
What's the DC voltage across the pop bumper switch when the pop bumper is not firing? That's the voltage that will be applied across the pop bumper solenoid once the switch closes.

Here's what the voltages around the bridge rectifier look like (taken from https://www.schoolphysics.co.uk/age16-19/Electronics/Semiconductors/text/Rectification_/index.html)
Rectifier voltages (resized).png
The AC voltage going into the rectifier from the left looks like a sine wave that crosses 0 volts 120 times per second (60Hz). The peaks are all positive voltage, but the valleys are below 0 volts, or negative voltage. The rectified voltage coming out of the bridge rectifier to the right (labeled as "unsmoothed" above) looks like a sine wave where all of the valleys have been flipped over to become peaks so you end up with twice as many peaks as the AC voltage, and no valleys.

The capacitor is there to try to fill the voltage gaps between the peaks while current is being drawn through the rectifier to fire the pop bumpers. The waveform looks more like the "smoothed" waveform above. The capacitor charges up on the rising edge of the voltage waveform, but it falls much more slowly that the voltage from the rectifier because it has saved up stored energy from the peak. The effect is a voltage that looks more like DC (because it doesn't drop below zero) than AC. It is not a smooth constant DC voltage like you might get out of a battery. The voltage fluctuation is call ripple. How much ripple you have depends on the size or capacity of your capacitor, and how much current you're trying to draw out of it.

It's possible that your capacitor failed or has developed an small short so that it no longer has the capacity to smooth out the ripple that it once had. So when new the capacitor provided a more "smoothed" voltage waveform but now is producing something with much more ripple that may look more like the "unsmoothed" voltage.

/Mark

1uf is a very small value and won't do much smoothing. Easy and cheap to replace anyway just to eliminate it.

The pop bumper spoon switches are probably burnt/pitted/tarnished.

I don't follow. Neither the transformer nor the other solenoids not in the rectified circuit will measure much DC voltage if any. They're all running on AC.

When the pop bumper switch is open the circuit through the pop bumper coil is open and no current is flowing. In that situation the capacitor can charge fully (assuming its working properly) and you might observe the maximum DC voltage across the switch that the rectified circuit can provide with little to no ripple. Once the switch closes, current flows through the circuit and the capacitor discharges to some degree between the peaks.

If your capacitor as a short, it might not be able to charge fully and what you would measure even in an open circuit is a lower voltage.

The rectifier circuit is almost certainly designed to provide a somewhat smoothed rectified voltage to the pop bumper for the fraction of a second it takes for the pop bumper to do its thing. But if you leave the pop bumper solenoid on much longer you probably draw current from the rectifier and capacitor much longer that it can sustain a smoothed waveform and it degrades into an unsmoothed waveform.

Multimeters generally aren't able to take instantaneous voltage measurements so they average readings over a period of time. That's why I asked how you measured voltage when the pop bumpers are firing. It seems possible that your reading might include some measurements taken before and/or after the pop bumper fired. If you kept the pop bumper active then you might be demanding more current than the circuit can provide which could also explain the low voltage reading. (Think weak car batter on a cold morning - there's just not enough juice in there.)

In any event, your voltage is reduced even though your measurements might not be accurate so try replacing the capacitor as pins4u suggested. And if you use a polarized capacitor be sure not to install it backwards.

If you do install it backwards it will let you know (boom)

Following. Please report the resolution. Thank you.

Just run down the list again to confirm nothing was missed....

1) Can you confirm visually that the capacitor is indeed marked "1.0uf" in size? That bridge rectifier arrangement in an application such as this usually has 100uf or 220uf or higher. (schematic could be wrong)
2) Can you set your meter to DC volts 200, and measure the voltage across the capacitor. It should be the +53VDC you seek.
3) Can you then measure the voltage across each of the 5 pop switches (while they are open) with your meter set to DC 200, and confirm that you see the same voltage, 53VDC which should be present if each of the coil windings are intact.
4) Measure the resistance across the fuse while it is removed from the game, with your meter set to OHMS. It should be ZERO.

Let us know what you find.

One more idea.... The bridge recifier might be partially out. If one of the four diodes inside of it is OPEN, then (because of the smoothing capacitor) you may see the power supply looking like it everything is fine WITHOUT any load (no pops running), but it would be acting like a HALF WAVE RECTIFIER under the load of a pop coil. So a full wave rectifies the input voltage at 1.4 times the input transformer voltage winding. A Half wave recifies the voltage at 0.7 times the winding input voltage.

Some back of the napkin math: If the the transformer is about 40 VAC, then if the bridge is 100% working, you'll get something like 55VDC when measured on the capacitor. BUT, if the bridge is half broken (one diode is out), then you'll get 40 VAC times .7 or about 25 VDC (under load) on the capacitor. Now add a slo-blo fuse of 2-OHMS and a 14-OHM coil, and that 25VDC will be reduced by 2/(14+2) or 1/(7+1)th, for a grand total of about 21.5 VDC on the coil when firing.

Replace the full-wave bridge.

Replace the bridge and the cap and take it from there.
They're cheap enough.

That capacitor is a snubber cap for RF spikes from coils. It is not smoothing the rectified waveform.

As mentioned earlier, you could have one leg of the bridge out. If you had an oscilloscope, you could look at the waveform and see what is going on.

Replace and report back. Also, double check the wiring to / from the bridge.

That cap won't be faulty - they almost never are. Perhaps the bridge is dodgy or you have other problems.

That's interesting. Can you elaborate? I agree that the cap seems small to do much rectifying but your comment makes me wonder...

- Without much smoothing, the pop bumpers are essentially running on rectified AC and not DC. Is that right?
- How would one effectively measure rectified AC without an oscilloscope?
- How are the RF spikes generated since the solenoids have diodes to handle the voltage spike when the switch opens?
- What is the potential victim of an RF spike? The bridge rectifier? Or was it an FCC thing?

Just another thought: Are you sure you have the correct coils in the pop bumpers?

I’d remove the DC side fuse and check the resistance from the fuse holder to each pop. I’d do the same thing for the rectifier wire that goes to each spoon switch. Since they’re all weak it’s got to be something common. You replaced the rectifier, so that’s ruled out...

Apologies if you’ve already done this and I missed it in the thread.

Dave

Great questions. I'll briefly elaborate and maybe others can chime in.
-Rectified AC has similar potential as regular AC with only positive waveform spikes. In theory, the positive peak potential is the same, but with less downtime between the waveform peaks. I'm not sure how this changes coil response. My guess, is it makes the coil respond faster.
-Without a scope, I would use the frequency counter on your digital VM to see what the waveform frequency is measuring. It should be double the line frequency (60HZ would be 120 and 50HZ would be 100).
-Switch gaps cause the RF spike. On SS games, it is not the low voltage switch contacts, but flipper switches and EOS switches. In EM games, all switches.
-RF Spikes cause noise in the power lines and without EMI filtering on the power line, it will radiate to other electronics. In SS games, it can also cause issues with low voltage electronics, microprocessor and so on. That is why there should be some RF filtering on MPU boards via LC and RC networks on the supply voltage lines.

Just order what PBR or Marco has. I use Mouser all the time, but you will drive yourself nuts trying to pick out the best cap if you are not familiar. Also, this should NOT be a polarized cap.

One more thing I thought of, most bridges have the sine wave symbol for the AC (input) and then the + / - for the rectified output. Do you have your wiring correct?

I totally get why that's important in SS games. I should have clarified that I was curious about EM games.

But why only address the DC (or rectified AC) switches and not all of the other high current switches in the game (stepper solenoids, reset solenoids, etc.). And was the RF spike a concern for nearby TVs and radios? Because I don't think anything in and EM game (other than maybe the rectifier and other diodes) would care.

Im interested on this as im getting ready to do a playfield swap on my OC. It was working perfectly before I tore it down. We'll see when i get it done.

This was a great explanation of how this all works. Thank you.

I doubt the concern was RF interference on other devices.

the diodes in parallel with the coils are the main snubbers that prevent high voltage spikes from potentially damaging the bridge diodes.

I dunno if the capacitor is there to absorb some of the energy dumped into the circuit by the collapsing magnetic field in the coil or if it's there to prevent the + rail from getting too low when the AC input voltage crosses zero.

I'd bet it's not there for smoothing the DC output of the bridge since that isn't very important when the load is just solenoids.

in inductive circuits without some kind of snubber, the high voltage energy is usually dissipated as a spark, and that only becomes an issue if you get a lot of sparking in a short time as the contacts will heat and vaporize ... so the EM guys didn't care and probably liked the light show.

the guy who designed in the bridge probably didn't want to be blamed when they died too soon, so he added the snubber diodes.

The only thing left is wiring. And since it's happening identically on all five coils, I suspect the positive line. Try this: Tack a piece of 16 gauge wire to the POSITIVE terminal on the bridge rectifier, and the other end to the POSITIVE side of any one of the coils (the lug that has the BAND of the diode attached). Then try manually firing that coil, using the associated leaf switch.

Just to make sure: did you measure the voltage between rectifier - and + or directly across bumper coil (both ways are OK)? Since there is a full wave rectifier, the coil common is not at the same ground as the AC solenoids, and if you measure against the AC solenoid ground, you will see only about half of the DC voltage.

if that improves things, suspect a cruddy fuse holder.

assuming the rectifier and fuse is on the playfield so no plug connections are in the path, you can try jumpering the wires on the fuse holder to bypass the fuse/clips.

Do you have a better picture of the rectifier connections since you replaced the fuse holder?

I tried following he wires from the original picture, but it’s at a sharp angle. I can also compare it to my old Chicago.

Dave

I hate to throw water on the enthusiasm, but swapping the CAP won't likely fix your issue. It could be OPEN, which would not have any material affect on the pops, or it could be SHORTED, which would show up when you measure VDC across it and would indicate ZERO volts. There really is NO in-between affect that the CAP could cause.

I think you might want to start at the top again and measure the various items we suggested. Your note right above shows very different values than your first pass at this.

The bright side: This is a fairly simple schematic. No real SS electronics involved. Just a power supply, a fuse, a coil and a switch. You are overlooking something obvious.

I’ve worked on early SS Williams machines that had the bridge male tabs soldered to the females. Directly soldered wires to the bridge tabs is best to avoid connection problems.

Whew!

My son in law’s Space Mission has sluggish pops. I’ll look into the bridge rectifier.