On Bally games with 7 digit displays, the display interrupt generator actually runs faster at 430Hz. These MPU boards have a different resistor at R21 for the 555 timer. See this thread with photos:
https://pinside.com/pinball/forum/topic/two-bits-mpu-with-flickering-strobing-displays-#post-5408121

If you bumped the HV to 192V and the pot was near the middle, it says the HV 160uF 350V capacitor is possibly ok. Measure how much AC ripple you're getting.

Check the "blanking" signal to the displays. Pin 10 on the display connector. It should be pulsing.

Yes, meter set to AC high voltage and a meter probe on each leg of that HV capacitor at the top left corner of the solenoid driver board.

Sounds ok to me. Anyway if you've got another Solenoid Driver Board, try it to rule the current SDB out.

Get a logic probe on that blanking signal I mentioned at the end of post #13.

Pin 10 at any of the displays. That signal is daisy chained from one display to another. It comes from the MPU board at J1 pin 10 and is an orange wire.

It should briefly pulse high at around 430Hz which is every time a digit is written to the displays. If you're getting 200kHz, that's way over the top.

What frequency did you measure on the pin 3 output of the 555 timer at U12? It should be around 430Hz.
BTW does this have a Bally MPU board or some aftermarket board? If it's a Bally board, what's the silkscreened date on the bottom right corner?

Your MPU board dated 1979 came from an older game with 6 digit displays so is running the display frequency generator (555 timer) at a slower speed. Some people will notice the displays on your game strobing a little and it might annoy them. Others less sensitive won't notice.

That blanking speed doesn't sound right. The blanking signal is software controlled by the display interrupt service routine that happens every pulse out of the 555 timer (i.e. in your case blanking should be around 343Hz).
I'll have to confirm this on one of my games later - can't do it at this minute.

With reference to the video in your first post, it shows all the displays flickering badly. Is this how it really looks on the game or does the flickering appear worse in the video due to camera sync artifacts?

What changed between it working and when the flickering started?
If the flickering is intermittent, have you wiggled connectors to see if there's any bad connections?

You won't find a 160uF capacitor. It's a non-standard capacitance value - strange choice back in the day really.
The part Ken listed is fine. I install 180uF, 105 degree radial caps since I'm not in the US.

While you wait for the replacement HV capacitor, reflow the current HV capacitor solder joints in case they're cracked - does happen. And while you're there implement the ground mod for it if it hasn't been done yet.

Order the capacitor Ken mentioned. It's a large physical size so should have a long life. Smaller physical capacitor size doesn't equal better.

Since you have an oscilloscope, you can visualise the ripple on the high voltage rail to the displays which will tell you if the HV capacitor is your problem.
First check if your oscilloscope can handle 200 volts and take care.
Make sure to set the X1/X10 switch on the oscilloscope probe to X10 so you don't damage the oscilloscope (this divides the input voltage by 10).
Set the oscilloscope to AC and highest voltage setting then adjust until you can get a reading.

Here are snapshots from my 6 digit display machine. Display Blanking and Display Interrupt generator speed are about the same (allow for variance/error in reading on my ancient oscilloscope).

Last picture is the high voltage ripple - I get around 300 millivolts. My high voltage is set to 180 volts.

DisplayInterruptGenerator.jpg
DisplayBlankingSignal.jpg
DisplayHighVoltageRipple.jpg

The AC ripple you previously measured indicated the old cap was doing its job. At least you have a fresh minty cap there now to last for years to come.

You should be getting around 430Hz out of the 555 timer now.

Can you measure the voltages at the test points on one of the displays BUT use TP3 on the display as your ground connection for the multi-meter.
Do test points TP1 (5V) and TP2 (190V) measure ok?

Might have blown the solenoid fuse on the rectifier board. The MPU board needs to see solenoid power at J4 pin 15 and uses it as the "Zero Crossing" signal. The last MPU LED flash on power up tests the presence of this signal.
If you reflowed that connector carefully check there's no accidental solder bridges on the pin header.

The feature lamp voltage is known to be a bit high in these games. As lamps illuminate (presuming you're using incandescents) the voltage will drop under load.

Half voltage is usually indicative of an open circuit diode inside the bridge. You need to disconnect the 600 ohm resistor (R1) that's across the bridge to test the bridge properly, otherwise you'll get misleading readings.