For using a 6-digit component board with a 7-digit panel, PIN #12 at J1 on the display needs to be isolated (cut trace that is connecting it to PIN #11) so there's not the contention with the blanking signal. A jumper then ran between PIN #12 & an aux board with 7th digit driver circuit on it (a level shifter, couple resistors, 2n5401 digit driver). That board would also need +5v / GND jumpers to it as well so the level shifter and digit driver could do their thing. The emitter of the 2n5401 would then get tied to the 7th digit pad on the 7-digit led panel.

Determined there's not a really clean way to do this that doesn't involve running additional jumpers or cutting that trace. There's a few ways I'd thought of doing a small aux board. Not saying any of these ways are going to happen, just thoughts surrounding it all.

1. Piggy-back at the J1 header since VCC, GND and you can split PIN #12 without having to cut any traces that way. Downside is, this gets costly with .156 Molex parts just to pick up a few signals & not sure people are going to want to pay an additional $5-8 per display for that type of kit. A wire jumper would still need to be soldered over to the digit panel's 7th digit pad.

2. Small narrow SMD board that gets soldered to the .156 J1 solder pads on the bottom of the board at PINS #12 (7th digit), #13 (GND) and #20 (VCC)... thinking finger-board style pads near the edge of the pcb. Could probably tack with hot-glue or use double-sided tape on the pcb. It'd probably hold with the solder joints alone. It'd have SMD components for the 7th digit circuit... and you'd then just need to route a wire over to the plasma pin for the 7th digit that's hopefully otherwise unused on a 6-digit component board. Alleviates cost of Molex part, but then at the expense of having to solder SMD parts. Another issue there is, no 2N5401 in smd packaging that I'm aware of. Would have to use a different PNP part available in SMD.. could present some issues there depending on voltage drop / transistor gain of the sub'd part & matching the other digit drivers.

Heck, you could roll-your-own with perf-board too or maybe wire all the components up off each-other old-school style

Not sure any of this is a worthwhile pursuit though, didn't seem to be much interest and/or viewed as "why bother" when I last brought it up.

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http://www.pinitech.com - "Pinball Inspired Technology"
NVRAM, kits, upgrades and test equipment for pinball machines

Are these conversion kits something people would like to see continue to be offered going forward? Just curious to get feedback there. Noticing lighter interest in recent months, not sure if that indicates people have moved on toward alternatives or most people with displays to convert have already done so.

I'll probably do one more PCB run for this year & then gauge further interest based on sales for the remainder of 2017. If interest remains light, I'll just figure most people would rather build the full kits than save $50 or so per set on these conversion kits. Good thing I'm working on a full kit myself now that I'm sitting on thousands of LED digits

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http://www.pinitech.com - "Pinball Inspired Technology"
NVRAM, kits, upgrades and test equipment for pinball machines

Well, I'm green with the conversion boards. But I am and had always planned to work on a FULL DISPLAY KIT since I started screwing with displays back in 2010. Just posted a sneak peek not to long ago here of what I'm working on. Targeting end of April on a full display kit if all pans out. They'll be priced right, they'll look nice and work well.

BOM and component sourcing is one thing, but the absolute easiest thing to do with PCBs is just to take what's out there that's already been done and assume it's a good design -- throw it into CAD and pump out products. That's not my intent here. I spent a lot of time load-testing on Bally machines before I did these conversion kits because there was speculation on whether the Bally machines with 3A regulators could handle the additional load. Along with helping me work toward an efficient circuit with old-school tech for the conversion displays, it opened my eyes to some things -- mainly that even popular aftermarket displays sold for years have some design issues or just aren't as energy-efficient as marketing hype claims.

Some examples..

BRAND "A" DISPLAY
Transistor gain issue that causes very high current usage per display (over 250mA per display). Brightness resistors also very low to pump brightness to the max since the displays are multiplexed.. again adding to high current usage. Best to not connect this one at the bench with signals faked without a current-limiting supply or you'll burn the leds out. Need the aid of the multiplexing while in the machine to pulse the current and prevent burn-out.

BRAND "B" DISPLAY
Brightness resistors set more reasonable here, around 24mA per segment, but the source driver IC can supply only 70mA max across its rails. This means the more segments that are lit, the less current available per segment. 7 segments lit = 10mA max per segment. Display is pretty energy efficient because it's limited by the IC max current, but also dimmer because of the current-limit occurring.

BRAND "C" DISPLAY
Energy efficient if set at a reasonable brightness, but brightness turned fully up and it's measuring 125-150mA per display. Depends on the user to adjust display brightness down a bit to achieve better efficiency.

Even some of the kits out there aren't that great IMO. Recently noticed that one of the kits seems to be an exact-match for another company's board layout/design.. so unless there's private labeling going on there it explains a few things. Interesting though in that it appears there are no current-limiting resistors for the led segments & if that's the case, the design relies on lowering voltage to the leds & multiplexing to "regulate" current to the leds. I've seen discussion of these types of circuits where people want to eliminate extra resistors & unless brightness is set around the forward voltage drop of the led, it'll be over-driving components and/or the leds. And voltage is not locked just above forward voltage drop, since it's a "feature" to allow the end-user to adjust brightness. Hard to say how that type of design holds up. Another kit just uses too low a resistor value to remain all that efficient, but I suppose the linear regulator can handle an extra 700-800mA as many displays out there are adding somewhere around 0.75A-1A load to machines.

My point is, people are building what they see enough of the time.. not questioning it, not trying their own designs, not understanding circuits & the variables involved. If someone designing displays is asking why WHITE/BLUE leds will not light as bright as AMBER, that's "LEDS 101" -- basic stuff, that if you designed an entire display by yourself you would know right off the bat. There's voltage drops over a number of components and it's all part of the calculations for an efficient design or to explain why setting brightness a certain way isn't resulting in the expected current usage. It's pretty clear to me enough designs in PCBs are just getting copied and thrown into CAD without much thought. And again, that's the easy part. Reminds me of bad code that gets copied over and over, pulled off Google and used in mission-critical apps inside companies, because enough people just grab code and don't try to understand what it's doing.

Yeah that seems to be enough of the problem with the 7-digit sets. I've thought of a clever work-around involving a piggy-back at the J1 header on the MPU, just not sure it'll work yet If I can do something that far up the chain, it'd mean only having a single wire to route around to the various displays to bring over the 7th digit signal to the 7-digit led panels that were mounted to 6-digit component boards. May allow one other mod to be possible as well..

At this point there's no way I'm not doing full kits...still sitting on most of the 15k digits I ordered end of last year and I don't plan to sit on them for the next 10 years

Might as well ask since it's been mentioned..

On a full kit, is there preference on single-board design versus the traditional 2-board design? I'm leaning toward a 2-board design out of the gate, at least for a DIY Kit. Not exactly a fan of seeing either components or solder points scattered around a digit panel myself.

Yep, I'm aware of 5 single board designs. A few that were sold in very low volume, many just in prototype stages. No idea who was first, doesn't really matter. But the advantage is eliminating the PCB, extra headers and possible right-angle brackets if the headers don't offer enough support. Amounts to *enough* costs that it's definitely on my radar.. even if just for boards sold fully assembled with SMD components on the back.

This won't be a problem. It'll be a completely separate design, no plans to have the conversion kit led panels mate with the component board.

Got you entered in the March contest Brian! Lost World looks great, thanks for taking some pictures!

I've actually planned to look into this mod some more & will be working on some ways to make it easier for people rather than cook your own board. Seems like it'd be a chore to perf board, might as well have a nice PCB for it I'll get to work on this as well & try to hit the same time-frame I'm planning with the full display kit (end of April). Not sure I'll throw it on the full-kit component board, but maybe a plug-in board at the display or at J1 on the MPU.

Actually in terms of the conversion displays, I hinted at this mod a few posts back. Using 6-digit component boards with a 7-digit panel.. it might seem a bit hackish to cut traces, run extra wires, have some piggy-back for the 7th digit enable circuit at each display. But if I can do the digit enable circuitry at a piggyback plug-in board at J1 on the MPU.. it seems like a single digit enable circuit could work for all the displays. Then I could throw this 4555 mod on there as well & the 7th digit output could then be wired to all the displays. It'd be an acceptable mod then I think and make sense to be using a 6-digit component board with games that already used 6-digit displays -- that need an additional circuit for the 7th digit. If that worked out it wouldn't require any additional modifications other than the wire ran to the 7th digit line of the 7-digit panel on the conversion displays. Only thing is you'd need power/gnd at the piggyback, so either a J4 piggyback would be needed to make it completely plug-and-play or power/gnd would have to be tapped elsewhere.

Yeah that makes sense.

I don't have the final board layout done yet for the full kits, so I'll see what I can work in there over the next few days

Hard to say, maybe not. In terms of using a 6-digit component board with a 7-digit panel for the conversion displays, there's cost advantage over the alternative options of having some plug-in board at the display or additional board to create the 7th digit enable circuit at each display + it allows this 6-to-7 digit mod to happen. This will likely go on the back-burner at the moment, especially considering things quieted down on conversion kits in general here in recent months -- let alone using 7-digit panels with 6-digit boards

Priority will be a full display kit and tying this 4555/4028 circuit into that.

So is this list below complete as far as Bally games that would benefit from the 6-digit to 7-digit mod?
Found these based on Oliver's notes @ http://www.pinball4you.ch/okaegi/pro_soft.html

HARLEM GLOBETROTTERS
DOLLY PARTON
FUTURE SPA
NITRO GROUND
SILVERBALL MANIA
SPACE INVADERS
ROLLING STONES
MYSTIC
HOT DOGGIN
VIKING

How about Stern games? Oliver's page mentions a divide by 10 for METEOR. Same 4555 setup for that?

Just trying to get an idea of things here..

Maybe the blanket statement is any 6-digit Bally games that had a sound board utilizing J1-7 at the MPU could theoretically benefit? The real question becomes whether there's divide-by-ten ROMs for anything other than what I posted above. If Oliver's the only one that was creating those even if additional games could benefit I'm not sure it'd happen for additional games.

STERN probably doesn't need the 4555 mod at all, if J1-7 wasn't wired on any 6-digit games.

Additional BALLY 6-Digit Games
Black Jack, Eight Ball, Evel Knievel, Freedom, KISS, Lost World, Mata Hari, Night Rider, Paragon, Power Play, Star Trek, Strikes & Spares, Supersonic, Voltan

Some of the above used chimes, so may be excluded.

Again.. just trying to get a handle on this. I've seen mention of this mod quite a bit over the years. Not sure on popularity and whether to just create some add-on piggyback board at J1 at the MPU or if there's enough games that benefit & interest to try to tie it into the displays. The downside to tying it into each display is it's 5x the circuits that are really needed.. seems like for the smaller sub-section of people that would actually utilize the divide-by-ten roms it may be better to leave it as a mod at the MPU J1. But I'm all-ears this week

Ok sorry guys the last few months have been a bit of a whirlwind for me as some have probably seen.

Since there were only 3x entries submitted for March & April, I'm going to send @Cheddar, RocketFromTombs & emsrph an nvram. Let me know what type you guys would like & I'll get those sent out to you. That'll close out the Retrofit Gallery Contest on these. Thanks everyone for participating! Of course pictures are still welcome from anyone building out the displays at any time, would love to continue adding more examples to the gallery

I'm nearly out of 7-digit pcbs, but still have 6-digit pcbs available so I'll be making the shopping cart link available again sometime over the next week or so for 6-digit sets. Until then if anyone's interested in picking up a 6-digit set, shoot me a PM/email.

Link sent!