Check all your connections / plugs.
Reflow solder on your headers.
Try again.

Is this the sequence shown in display test mode?
What's the very first number you see when you start display test mode?

yes...this is the exact sequence.

I can't do this myself unfortunately. might post some pics to show the displays, see if you think it needs work.

So are you saying in display test mode, the intended numbers on the left are producing the numbers on the right?
000000 --> 000000
111111 --> 333333
222222 --> 444444
333333 --> 777777
444444 --> 666666
555555 --> 888888
666666 --> 999999
777777 --> 000000
888888 --> 111111
999999 --> ?

If not, please be very specific so we can try to determine the logic of what's going wrong.

Correct.

deleted

Can you post a video showing all five displays in display test mode going through the full number sequence a few times.

At the moment I only have this video. If you want longer I’ll have to do this tomorrow as I’m at home today and the pin is at work.

That video much better illustrates the issue.

There are 4 signal wires from the MPU board that tells the displays what number to show. These four signals form a BCD (Binary Coded Decimal) number.
It looks like you have an open circuit on one of those signals to Player 1 and the Credit/Match/Ball in Play displays.
Specifically speaking the BCD data 1 signal.

It's likely you have fractured/cracked solder joints on the display pin header. If you post clear pictures of the display pin header soldering it should be obvious if they're cracked
Secondly check and re-crimp (if found to be bad), the crimp terminal at pin 18 on both of those displays which is the BCD data 1 signal. That crimp is a Blue-White wire.

Thank you for the detailed reply mate, very much appreciated the replies.

I'll look tomorrow when at work and reply with photos or other questions.

Quench so far so good!! Nice work mate. Pushed back in pin 18 on both score 1 and credit and got both back working/scrolling as they should!! Photo shows how little they were out.

So happy this was an easy fix!! Legend!! Thank you!

Photos of the underneath of these displays for you, not sure if needed now they work well. I still have a digit out on the credit display? So if you have any idea on that!

And obviously score 4 still not working.

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Bit strange you had two connectors with the same problem but anyway, good going.

It looks like someone has already resoldered those pin headers in the past.

Firstly if you move that display to another position does it work?
If not, missing digits is most commonly caused by resistor burnout on the display board. The displays have a 100k ohm resistor for each digit. These are at R1, R3, R5, R7, R9 and R11.
If you have a multi-meter, set it to resistance mode. If your meter isn't auto-ranging set it to the 200k ohms resistance range.
With the display on the bench (out of the machine) put a meter lead on leg of those resistor - they should all measure in the 100k ohms range. Resistor R3 is specifically for the 10's digit.

They look ok to you though? Don't need to resolder at all?

So changed around the displays and the fault followed the display.

Readings as follows:

R1 - 77.5
R3 - Started at 12, was creeping up to 22 when I got bored (guessing this needs replacing?)
R5 - 88.6
R7 - 83.5
R9 - 133.5
R11 - 102.8

They look ok, but I can't 100% tell from the pictures. Maybe if you're able to take daytime pictures outdoors but out of direct sunlight say at a 45 degree angle at the pin headers soldering only I might see more detail.

Was this 12-22 ohms, 12k-22k (kilo) ohms or 12M-22M (Mega) ohms? i.e. did the meter indicate a 'k' or 'M' ?
Some of those other resistors have gone out of spec. Ideally these all need to be replaced and you should check the other displays too. These resistors are a common failure. Original spec was 1/4 watt resistors but should be upgraded to 1/2 watt resistors.

Some examples of display pin header cracked solder joints to look for. A magnifying glass will help.
Click the images to zoom in:

IMG_0043a.jpg
IMG_0052a.jpg

anyone have a spare Future Spa backglass laying around? (or a decent res scan to print a translite for temporary?)

Try these forums:

https://pinside.com/pinball/forum/topic/looking-for-backglass-and-translites-thread-buy-sell-trade

https://pinside.com/pinball/forum/topic/future-spa-club-come-on-in-the-water-is-warm

thanks Jethro - appreciate the heads up.

Flipper coil number is AQ-25-500/34-4500. Found a AQ-25-500/34-5050 among my spare parts. Is it close enough as a replacement?

It should work fine. There are two windings, the -500 is the "flip" winding that kicks the ball. The -4500 (or -5050) are the windings used when the flipper is held on. Both coils should produce the same power when kicking the ball. I wouldn't suspect you will have a problem when the flipper is held on with either coil. Will you try it and report back?

AQ-25-500/34-5050 flipper coils were originally used in early solid state games that had chimes up to Strikes and Spares (according to the manuals). The Lost World manual is the first to list the AQ-25-500/34-4500

Can’t get a plastic coil sleeve to fit in the 5050. Hole is just a tiny bit narrower.

A metal sleeve fits but a bit old school for a replacement..

Something is out of spec either your sleeve or the coil bobbin then.

Sandpaper and round dowel.

Sandpaper did the trick..
No noticeable difference in strength between 4500 and 5050 when flippers are held on.
Thanks for helping me out.

I seem to recall reading about some slight differences in the Bally -35 boards where resistor values were changed to alter the display timing. Is that documented somewhere on what values were used with each machine? Also, any other differences in the -35 boards that may cause issues with moving boards around? That may explain an issue I see with at least one of the two troublesome boards I have left to fix.

I've been working through a stack of -35 boards (history unknown) and have all of them working perfectly except for 2 boards. They boot fine on the bench and run ok in my Elektra but both have different odd behavior. My Elektra has proven to be a good machine to run boards that look ok on the bench and if anything is even slightly off will show up in that machine.

Board #1 - This one runs and plays fine in Elektra. However when getting to the lower playfield 3 lamps are stuck on with this MPU installed. PIA's were tested and swapped with another board with no change. Going to go back over this board with Leon's test ROM with both the logic probe and scope to compare to a known working board. Once the lamp issue is resolved this board should be good.

Board #2 - This is an odd one. Board boots and run fine in Elektra. All lamps work and game plays well. I just notice that when this board boots that the startup sound I normally hear is different from all the other MPU boards so something is off. Otherwise it seems to work ok. Once I get that fixed this one should be good too.

Even though these do run they aren't done until they pass my Elektra test. If anyone has seen similar symptoms what did you find?

See here with pictures down on further posts showing the different resistor for 7 digit games.
https://pinside.com/pinball/forum/topic/two-bits-mpu-with-flickering-strobing-displays-#post-5408121

Thank You! Will keep that in mind and make sure to install the appropriate resistor for the game it is going in.

My Medusa (7 digit displays) with a timing resistor on the MPU board for 6 digit games plays noticeably different. The display attract mode is much faster, the bonus countdown is faster and the playfield display extra ball matching feature counts much quicker making extra ball more difficult to achieve.

#1 cpu check the 5101 ram... lamps are controled by the 5101 ram cells.

How do you reset the high scores please guys? I have a HGT set at like 945000. I'd like to reset to have mine there.

Thought I saw it in the manual but can't seem to find it second time around

Hit the little red self test button switch inside the coin door about 9 times until you see the number 4 in the Match/Ball in Play display.
On the MPU board in the upper right corner is a little red switch marked S33. Press it to clear the Highest Score to zero. Then press the start button on the front coin door to set the Highest Score to the value you want.

See "III. BookKeeping Functions" in the manual (paper page 3, electronic PDF page 7)

Still having slight issues with my double flipper. The top one needs a good push to active it! So with a quick flip, it doesn't flip.

I've attached photos of the flipper eos's as well as the spacing for the flipper button on the cabinet.

Should I just replace? Or is my spacing wrong? Or is there something else.

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gapping doesn't look bad though the switches look kinda worn, you cleaned them I assume? Maybe it's worth trying to replace the top Switch that activate your upper flipper with a new one?
https://www.pinballlife.com/bally-secondary-end-of-stroke-switch-normally-open.html

I concur.

Thanks hisokajp

I did a full flipper rebuild but because my soldering skills are so so I didn't replace the switches! So I'll do that, thanks guys!

Replaced the switches on both right and upper left! Works perfectly now!! Thank you! Next time I do a flipper rebuild on an old girl like this, think I'll do the switches as mandatory next time!!

Both boards are fixed! As suggested one was a flaky 5101. Oddly that passed both the Built-in test and also outside with a Neoloch tester. Usually they are bad when they say they are bad but sometimes bad ones get through those tests. Replaced and that baord fixed.

The other board had a bit of hidden corrosion under the solder mask and under R1 and R3. Passed a normal bench test and ran in my Elektra but I could tell it was off from the original board. After removing those resistors, dealing with the bad trace, and installing new resistors that board it done too.

So definitely some things for everyone to check and even if you 5101 tests goo in multiple devices if your board is acting up swap it out anyways...

Was the 5101 a Chinese remark or original?

I have also had a 5101 that tested good in the Neoloch and Bally's POST yet caused a display problem in game. Caused some digits to shift over to the left. Pretty sure it was original from an 70s or early 80s pinball. Rare but it happens. Hard to guess what the fault in the chip was.

It was an original as far as I can tell. Was an AMI chip. I went through some others and and also found an RCA branded one that also caused weird behavior in Electra. I think I’m going to try running all my spares in that game as a way to weed out any other flakey chips.

If I get any remarked chips in from any supplier I’m just going to return them. Run into too many issues with 6821 chips that it isn’t worth it.

Bally OEM coil sleeves for Bally products are 1/2" X 1-11/16"
Wico #56-073400

Now that Marco's has finally dropped the price of shipping I'm stocking up on some much needed parts.

Can anyone confirm this is the right switch for my Harlem flipper please: https://www.marcospecialties.com/pinball-parts/A365-00046-0000

Thanks again guys.

Looks good to me.
That switch assembly is for the lower left flipper.
Bally OEM was two separate switches put together to make a "break-then-make"
EOS switch.
All other flippers should have single EOS switches.

Am I having a Switch Matrix issue? Game is Centaur.

Issue: The "O" of the O-R-B-S and the "2" of the 1-2-3-4 drop targets do not register if they are the last one hit in each of their banks.

All eight target switches can be seen in Self Test, and in play, the "O" and the "2" register fine as long as they are hit first, second, or third of their respective 4-bank (issue is only when they are the last to fall). Also, though very seldom, the "1" of the 1-2-3-4 will not register even if it is dropped first.

One thing I observed, maybe helpful(?) : when the "2" is the last target down in the 1-2-3-4 and the switch has failed to register, if the "Spot 1-2-3-4" standup switch is hit, it will fire the plunger for the "2" drop, as it would if it thought the "2" was the next target to drop (but the "2" is already down so nothing happens).

The switches are definitely making contact when targets are dropped, verified w/ DMM. Also replaced the diodes on the "O" and "2" switches.

All eight switches are on the same strobe line.

Where should I look next? U10 6821 PIA?

use switch test and at the mpu connector short from strobe to return of the problem switches and see what numbers you get. PIA caused switch failure is usually something like everything in column two registers as being from column one or nothing in row 3 registers, but that same symptoms can be a playfield / wiring issue. Normally you can isolate the issue to being on the PF or the MPU by checking switches right at the MPU plug.

If you have a known good 6821 fairly not invasive to try. Also if you have a switch MPU PIA problem likely other issues with lamps or displays would happen because the same PIA ports controlling switches do multiple things like lamps.