Bally AS-2518-17 MPU cursed

(Topic ID: 145080)

Bally AS-2518-17 MPU cursed


By falco

2 years ago



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  • 32 posts
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  • Latest reply 2 years ago by falco
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#1 2 years ago

Recently, I've been having a lot of 'fun' with an AS-2518 MPU board. It's reasonably tidy, but came in a machine a friend of mine bought non-running. Initially, it had the LED stuck on, but after having slowly worked through a bunch of problems (resistor in reset circuit cracked, bad RAM, etc) I've reached the point where it's giving me flash codes. However, it only ever gets to four flashes, the fifth one is eluding me. It currently has the original ROM set for Mata Hari in it. I've tried known good replacements for every socketed IC, swapped the PIAs, etc, but nothing changes. Giving it the ROMs out of Cosmic Princess results in the same behaviour, fails at the fifth flash, though with those ROMs sometimes the LED is stuck on instead of a flash, or flickers then goes out. Very strange.

Specific weirdness - fifth flash is U11 PIA failure. But, that's the PIA that's driving the LED that's flashing, so address lines, chip select etc. must be OK, right? I've metered out various connections, e.g. data bus, seems OK too.

Any ideas? I really want to get rid of this board...

#2 2 years ago

Have you tested the PIA, or put in a known good PIA?

#3 2 years ago
Quoted from falco:

Specific weirdness - fifth flash is U11 PIA failure. But, that's the PIA that's driving the LED that's flashing, so address lines, chip select etc. must be OK, right? I've metered out various connections, e.g. data bus, seems OK too.
Any ideas? I really want to get rid of this board...

PIA failure can be a single output. You can have a bad U11 and that will flash the LED, but fail the power on self test.

Also try disconnected all the outputs. It is possible to have an issue on another board cause the power on self test to indicate PIA failure. You can try to boot the MPU with only J4 connected and see if it gives u 7 flash.

#4 2 years ago
Quoted from jwilson:

Have you tested the PIA, or put in a known good PIA?

Yep - tried 6820s, 6821s, swapping the two existing PIAs, but haven't sacrificed any livestock yet. I've cycled through about ten PIAs in my desperation.

Quoted from barakandl:

PIA failure can be a single output. You can have a bad U11 and that will flash the LED, but fail the power on self test.
Also try disconnected all the outputs. It is possible to have an issue on another board cause the power on self test to indicate PIA failure. You can try to boot the MPU with only J4 connected and see if it gives u 7 flash.

This is on the bench - the board behaves the same way in a machine, though. Re failure on a single output, I wouldn't expect the self-test to look at outputs? Re the LED flashing, sure, I was only using that as proof that the addressing/CS was correct. It proves at least that the PIA is accessible to the MPU at the right address. Presumably the self-test is failing to read back the contents of one of the registers (I think that's all the self test does), which suggests that one or more of the data lines are bad. That certainly would correspond to the symptoms - provided that bad data line wasn't used when setting the PIA up to flash that single output, the LED would behave fine. I have metered out the data lines, and in theory they must be reaching the other PIA (U10) OK, as that one passes self-test. Maybe I missed something when I did that, but it seems unlikely. Bah. 2518s always give me problems!

#5 2 years ago

An easy solution would be to buy a new Alltek board.

They are awesome!

I have a spare one, if interested.

#6 2 years ago

Ha, given that I mainly do these repairs because I enjoy bringing dead boards back, that would be a bit counter-productive!

#7 2 years ago

Thought I'd give it a shot...knowing most Bally 17 boards are usually pretty crusty these days.

The Allteks are pretty nice/reliable though.

#8 2 years ago

Yep - I've actually been pondering designing/making a low-cost alternative. It could be pretty budget, e.g. no silk screen, but if built with good quality sockets etc. there's no reason why they wouldn't be as reliable as any other board. Would probably change a few things, e.g. 74 series logic, different clock, redesigned reset, single non-volatile RAM - just common-sense stuff, no bells and whistles. The problem with the Allteks is the exchange rate. US$ are too expensive in NZ these days! Of course, I have so many other projects oh that I'll never get time to do it.

#9 2 years ago

I am learning PCB software and have been kicking around the idea of a replacement MPU budget style. The BOM on a bally MPU setup like the altek is pretty damn low. I have successfully relaid out the -51 sound board that is in proto phase which gives me confidence I can do the Bally MPU.

For the -35 replacement with maybe mpu-200 support....

Do a 6802 cpu and crystal to eliminate that damn clock generator circuit and the 6810 RAM.
Pads for 6264/NVRAM in SMT SOIC-28 and DIP28 (i am not sure if i know how to make this compat with MPU200 and -35 ram setup).
Single EPROM 2764 or 27128
Resistor/cap networks to eliminates large numbers of discreet resistors/caps.

Assembling the boards would be the biggest issue unless i try and pay someone to do it for me. I am also thinking about offerning them as DIY assembly pcb kits that include the blank pcb and all the parts to assemble.

#10 2 years ago

The last time I ran into a frustrating mystery problem, there ended up being an issue underneath a socket that I hadn't replaced yet.

#11 2 years ago

Definitely MPU200, I think. I'm not sure whether the CMOS RAM difference is an issue; it might be, but so long as AS-2518/MPU100 code completely ignores the extra RAM, it might be fine. I don't know any more than you do though!

Re the RAM generally, I'd probably use a single NVRAM module to replace all the RAM (6810 and 5101), so that either a 6802 or 6808 could be used. Could afford to be a bit wasteful of RAM, in order to end up with a simpler design.

Single EPROM - definitely. Downside being that there'd have to be ROMs burnt specifically for this design, though this was something I was also thinking was the best approach. Mind you, I have an EPROM burner, and many people don't, so maybe I'm being a bit selfish...!

Resistor/cap networks - sure, why not. Anything to simplify, tidy, shrink. Mind you, just losing most of the reset and clock components would help a lot. Of course, you could go to PLCC 6821s too, but that might be going too far.

Board assembly - probably easiest just to farm out the production. There are places that you can send your design, and have it assembled professionally - SMD, ROHS reflow soldered etc. But as to cost, no idea. I'm so lazy, no research on that yet. Maybe I'll have a look tonight if I get a chance.

DIY - sure, would dictate design to some extent though. You'd probably have to go for through-hole components rather than SMD, but maybe that's not a major issue.

#12 2 years ago
Quoted from ForceFlow:

The last time I ran into a frustrating mystery problem, there ended up being an issue underneath a socket that I hadn't replaced yet.

Yes, it's quite likely it's something like this. Someone's done some work on this board in the past (U11's socket has been replaced). It looks like good quality work, but who knows. I'll investigate further tonight.

#13 2 years ago
Quoted from falco:

It's reasonably tidy, but came in a machine a friend of mine bought non-running.

Nice to see I'm still your friend.

However the board actually ran perfectly ever since I got Mata Hari from NYC, maybe 18 months ago or so. Then one day .... Baaaabaaaaa ....

I know you can do it Mikey! The Faith is strong!

rd

#14 2 years ago
Quoted from falco:

Yes, it's quite likely it's something like this. Someone's done some work on this board in the past (U11's socket has been replaced). It looks like good quality work, but who knows. I'll investigate further tonight.

Good idea to suspect the previous work.

Quoted from falco:

Definitely MPU200, I think. I'm not sure whether the CMOS RAM difference is an issue; it might be, but so long as AS-2518/MPU100 code completely ignores the extra RAM, it might be fine. I don't know any more than you do though!
Re the RAM generally, I'd probably use a single NVRAM module to replace all the RAM (6810 and 5101), so that either a 6802 or 6808 could be used. Could afford to be a bit wasteful of RAM, in order to end up with a simpler design.
Single EPROM - definitely. Downside being that there'd have to be ROMs burnt specifically for this design, though this was something I was also thinking was the best approach. Mind you, I have an EPROM burner, and many people don't, so maybe I'm being a bit selfish...!
Resistor/cap networks - sure, why not. Anything to simplify, tidy, shrink. Mind you, just losing most of the reset and clock components would help a lot. Of course, you could go to PLCC 6821s too, but that might be going too far.
Board assembly - probably easiest just to farm out the production. There are places that you can send your design, and have it assembled professionally - SMD, ROHS reflow soldered etc. But as to cost, no idea. I'm so lazy, no research on that yet. Maybe I'll have a look tonight if I get a chance.
DIY - sure, would dictate design to some extent though. You'd probably have to go for through-hole components rather than SMD, but maybe that's not a major issue.

If you run Bally -35 software on a Stern MPU-200 with both 5101 rams installed, you can have odd issues including corrupted audits. I am not sure how this translates to using a device like FM1608. Maybe a dip switch bank to flip between MPU-200 RAM and clock speed.

I wouldn't know how to combine all the RAMs to use just the FM1608/6264 footprint. Not that it would matter much, i would use 6802 since i have a bulk amount of them on hand. I suppose no big deal to atleast include pads to install a 6810 RAM if using a 6808.

#15 2 years ago
Quoted from rotordave:

However the board actually ran perfectly ever since I got Mata Hari from NYC, maybe 18 months ago or so. Then one day .... Baaaabaaaaa ....

Really? Cripes! Are you sure? I thought this one was ex-Italy! Maybe that's just because someone's written Genaro on it. I so lose track. I think it was the other one that ran fine for a few hours then died again, too. So mixed up...

#16 2 years ago
Quoted from barakandl:

If you run Bally -35 software on a Stern MPU-200 with both 5101 rams installed, you can have odd issues including corrupted audits. I am not sure how this translates to using a device like FM1608.

Interesting. I've always assumed that the MPU200 used two 5101s to get a full byte wide data bus; finally got round to verifying that. I can imagine that the 4-bit models assume that the unused bits would always be low (I think), and if they aren't, unexpected things could happen. If that needed to be forced, it could be a bit tricky, but it could be done with a bit of logic I guess.

Quoted from barakandl:

Maybe a dip switch bank to flip between MPU-200 RAM and clock speed.

Yes, sounds like that'd be required. Or take the coward's way out, and build two variants based on the same board - one AS-2518/MPU100, and one MPU200.

Quoted from barakandl:

I wouldn't know how to combine all the RAMs to use just the FM1608/6264 footprint. Not that it would matter much, i would use 6802 since i have a bulk amount of them on hand. I suppose no big deal to atleast include pads to install a 6810 RAM if using a 6808.

If I wanted to be lazy, it would be possible to use a single 64kx8 non-volatile RAM IC, and just have it selected when nothing else is. That way, all otherwise-unused memory locations work as RAM. That would work OK, but isn't very nice design, and doesn't address the 4-bit 5101 bus for AS-2518 style boards.

#17 2 years ago
Quoted from falco:

Really? Cripes! Are you sure? I thought this one was ex-Italy! Maybe that's just because someone's written Genaro on it. I so lose track. I think it was the other one that ran fine for a few hours then died again, too. So mixed up...

Yep, promise.

The Italian ones were Flash Gordon and Big Game.

Big Game is going like a rocket! You'll be playing it on Sunday.

rd

#18 2 years ago
Quoted from barakandl:

I wouldn't know how to combine all the RAMs to use just the FM1608/6264 footprint. Not that it would matter much, i would use 6802 since i have a bulk amount of them on hand. I suppose no big deal to at least include pads to install a 6810 RAM if using a 6808.

To combine the RAMs you can just put the NVRAM on the bus and select it in the right address ranges. The trouble comes in the address decoding part. That's where you're going to need some kind of PLD. It doesn't really make sense (IMO) to "redesign" an MPU and use 74 series logic for the address decoding and other basic logic functions.

The other issue is the requirement by some Bally code to have a 4-bit RAM with the higher data bits tied high. You could wrap up the 4-bit/8-bit RAM switching in PLD, but it might be cheaper/easier to use two 8-bit buffers like the Alltek MPU. Using that method you could get away with a GAL16V8 for the address decoding, making a pretty simple design.

Here's an example partially finished layout. I'm doing the address decoding, RAM compatibility, and PIA output multiplexing in one CPLD. Display interrupt generator, zero cross, and clock circuits not shown. This example is mid way through a design that I did for this MPU. In the final design I broke down and added 128 DIP switchable ROM banks. Too many projects in the queue before I get to this one though... maybe next year.

Bally_MPU_PCB_Partial_Layout.jpg

#19 2 years ago
Quoted from Lindsey:

It doesn't really make sense (IMO) to "redesign" an MPU and use 74 series logic for the address decoding and other basic logic functions.

The only argument I have against a PLD is serviceability. It means that in many cases, once that goes faulty, the board is junk. As opposed to the original boards, using all off-the-shelf logic, which were repairable by anyone with the ability to solder and source parts. These days, some of the bits are harder to get, of course. My thoughts were that for AS-2518s, they use so little logic that I'd be OK with using common 74LS parts. If I were trying this with something like a System 11, I'd probably give up due to the large number of logic ICs, and consolidate in the way you're describing.

Additionally, I guess there's a question around the use of the word 'redesign'. My intention was to avoid any unnecessary changes, making the board as similar to the original as possible. There are a few things that just make no sense at all to leave as they were, i.e. the clock design (hard-to-find IC, not very accurate), and reset (too many components, replace with a simple reset monitor). Both of those could be replaced with very common off-the-shelf alternatives, so they seemed like a good idea.

So many different approaches that can be taken to this. In all the time I've spent thinking about it over the past couple of days, I could have repaired the original one, almost certainly!

#20 2 years ago

If you don't like PLD you'll really hate the fact that I used a microcontroller for the display interrupt generator and display blanking delay circuit

PLD hasn't hurt Alltek's sales, but there's obviously a market for the original design as well because exact replicas are also currently available. You can mitigate the serviceability issue by publishing the JED file for the PLD. It's not as simple as replacing a 74 series IC, but not un-fixable.

I tried to use the microcontroller to also generate the two clock speeds, but it didn't work that great because the MPU-200 clock speed is not divisible evenly with the PICs internal clock. If you only wanted to do the slower clock speed (500Khz) you could use a PIC 10F320 and provide the display interrupt with a PWM pin, clock the 6802 with a clock output pin (PICs can be configured to output the internal clock on an IO pin at 1/4 speed and has an internal clock up to 16Mhz), and still have two pins and enough CPU to do the little circuit on the display blanking. The PIC running at 8Mhz would drive it's clock out pin at 2Mhz which would then be divided by four again inside the 6802 to give the 500Khz clock which would then be present on the E pin of the CPU. That would eliminate a whole bunch of passive components and a few ICs using a single ~$0.75 part in an 8 pin DIP package, buuuuut... you have another non-off-the-shelf part in there. And you would have to write and test the microcontroller code. Sometimes it's easier to just duplicate the original.

It really depends on what you want to build. If you're only going to do -17, -35, and MPU-100 compatibility using a 6802 configured for internal RAM, it's easy enough to do it with basic logic. If you want to add MPU-200 and 6808 compatibility, it get's more complicated. I took the approach of minimizing parts for easier assembly and offering compatibility for all Bally/Stern titles. In terms of reselling for profit, the assembly time and parts count are areas where a lot of cost can be saved (IMO). Eliminating a lot of passive components is pretty compelling if you're using DIP parts and hand assembling them.

#21 2 years ago
Quoted from Lindsey:

If you don't like PLD you'll really hate the fact that I used a microcontroller for the display interrupt generator and display blanking delay circuit

Ha! I'm mortally offended! Using something faster than the core MPU just to generate the display timing!! What's the world coming to...

Seriously, I don't mind the PLD approach. I'm just a bit traumatised by all these boards I've encountered in the past that have made me go 'ah crap, undocumented custom IC, no point in putting any effort into this piece of crap, mumble mumble'. You are right, publishing the equations etc. would mitigate it well enough. At least then most people could find someone vaguely local to burn a replacement for them.

Quoted from Lindsey:

only going to do -17, -35, and MPU-100

Yep. I don't often see MPU-200s. There must be far more of the earlier ones around. Maybe it wouldn't be worthwhile supporting those. Oh well, I'll ponder. It's not as if I'm thinking about doing this anytime soon.

#22 2 years ago
Quoted from falco:

Yep. I don't often see MPU-200s. There must be far more of the earlier ones around.

Correct, there aren't many M-200 machines here in NZ. There are a few Meteors and not much else. There was an Orbitor1 I used to play at Rainbows End when it opened in the 80s.

I think the amusement industry here was making so much money from donkey kong and Galaxians in the early eighties, they didn't bother too much with pinball machines. Plus the huge import taxes there used to be pre 1985 (As opposed to Arcades which were made here with imported boards, thus bypassing most of the import tax)

rd

#23 2 years ago

PLD design would be not servicable by me and i have rebuilt probably 250+ original bally MPU by now. I would definatly use the original 74xx/4xxx ICs because i have the board damn near memorized.

The bally MPU is not complex at all. There is 6 small ICs that are still available for the most part. The MC6821P is still far more obsolete than a 4502.

The display generator circuit is sooooo simple. I just don't see why to reinvent it.

#24 2 years ago

If the price is right people are not going to care if there's programmable logic on the board. Especially when it allows you to offer features which would not otherwise be available. Alltek has sold several thousand of them, I'm sure, and no one complains about the design. Being simple doesn't really factor into it. An IC with no external components is simpler by definition than a 555 timer circuit. The whole MPU is very basic. Like I said, I designed it to make assembly more efficient. About 10 less passive components to bend the legs, stick through the holes, solder, and clip the legs by adding the PIC with no additional cost. Seems like an obvious choice to me. I'll offer a warranty on the MPU, publish the .bin file and offer programmed PICs for $1. Problem solved. The time to install those passives adds up fast. Installing all of the resistors used in the MPU with DIP packages is going to be a nightmare. I knew that with this design there might be a hope that I would actually assemble a bunch and sell them. A direct dupe of the original would have been a lot easier to design, but there's no way in hell I'm assembling a dupe of the original design using DIP parts because it would take FOREVER and I would make nothing, even at $199.

Same thing with the clock and zero cross detector. They're very simple too, but there are "better", more efficient ways to do it using less parts which don't need PLD or a microcontroller. If you're planning to go into large scale production these changes will make a big impact to the overall cost because assembly is going to be a big chunk of the cost with something like an MPU. Especially if you're doing it yourself. Every minute you save is more profit in your pocket. If you're planning to have them assembled, they're going to be pretty expensive using so many DIP parts. On a small scale like this, you're going to spend an arm and a leg having them assembled offshore. The time saved by shaving off a ton of passive components and ICs is considerable. Anyone who's ever assembled one of the kits from Homepin knows what I'm talking about. Obviously, the biggest obstacle to any of that is knowing how to program PLDs and microcontrollers, but that's really worth exploring because then you have the options to do all kinds of things in pinball. The problem with rehashing what's already available and undercutting the price is that anyone can do it and pretty soon you're all competing for peanuts. I'm surprised this hasn't happened with MPUs yet. Especially Bally, but I assume the assembly effort is what stops people. It's definitely not the complexity.

I'm not trying to convince people to do it my way, but I do have good reasons for doing it the way I did which will work best for me in the long run. I could offer these things REALLY cheap if I wanted to, because the assembly will be WAY cheaper than a conventional design with DIP parts. I was also able to get the total size of the board way down. That's also going to be a big cost savings if you're not ordering the things in 1000+ quantities. All of this stuff adds up to my boards being cheaper to build than the "competition" by a considerable margin.

I started out thinking about offering a "basic" MPU as well without MPU-200 compatibility or ROM for all of the games but then I started thinking that adding ~$5 in parts could add $50 to the final sale price so I went with that option but who know's if I'll ever sell any. I'm working on other projects for the foreseeable future.

#25 2 years ago

The main reason I would use the NVRAM to replace the 6810 rather than using the RAM inside the 6802 is because I've seen the RAM inside the CPU fail a lot more often than the CPU itself. If I were using pulls, I would avoid using the RAM in the 6802 for that reason.

#26 2 years ago
Quoted from Lindsey:

If you're planning to go into large scale production these changes will make a big impact to the overall cost because assembly is going to be a big chunk of the cost with something like an MPU. Especially if you're doing it yourself. Every minute you save is more profit in your pocket. If you're planning to have them assembled, they're going to be pretty expensive using so many DIP parts. On a small scale like this, you're going to spend an arm and a leg having them assembled offshore. The time saved by shaving off a ton of passive components and ICs is considerable. Anyone who's ever assembled one of the kits from Homepin knows what I'm talking about. Obviously, the biggest obstacle to any of that is knowing how to program PLDs and microcontrollers, but that's really worth exploring because then you have the options to do all kinds of things in pinball.

Fair enough. I understand the benefits... Even assembling the -51 sound board takes me a little over an hour. The assembly time is for sure the bottleneck of something like a MPU. I am kicking around the idea of having china assemble the boards for me... at that point i would need to at least go to all SMT devices except for the obsolete stuff. I would just have china install a DIP socket for the CPU, PIAs, and EPROM.

The other idea is to offer the blank board and all the parts as a "kit". That could introduce its own problems.

Quoted from Lindsey:

The main reason I would use the NVRAM to replace the 6810 rather than using the RAM inside the 6802 is because I've seen the RAM inside the CPU fail a lot more often than the CPU itself. If I were using pulls, I would avoid using the RAM in the 6802 for that reason.

I have gone through 1000+ of MC6802P used pulls and i can't recall more than once or twice a used pull had a good CPU but the internal RAM was bad. I test the CPUs in a WMS MPU that uses the internal RAM.

On the otherside of this equation.... the MC6808s have functional internal RAM a good portion of the time even though they are marked as 6808. The fairchild and AMI 6808 never work as a 6802, but the moto ones do. I suspect at some point they where marking 6802s as 6808s just to fill orders.

#27 2 years ago

Personally, I think the proper "re-design" of the Bally/Stern MPUs would be to eliminate the 6821 PIA and to use a PLD if possible. At some point, production quantities of those PIAs is going to disappear or at least drive the cost way up.

In my opinion, the sale of this type of board is going to come down mostly to Cost, Software (all games titles included), and reliability. I think the bulk of alternative sales of MPUs has been to two main markets.

1. The professional restorers that just want to pop a new board in and know the MPU is not going to give their customer issue in the future.

2. The home collector without the electronic skill set to trouble shoot, repair, or solder an older board. The just want to pop in a new one and be done with any issues.

While #1 probably has the knowledge, file data base, and Eprom Programmer, they probably don't want to fool around with burning roms to match each game. Much easier to just set a dipswitch. #2 more than likely does NOT have that skill set or equipment and would also like the ability to move the board from game to game. Both, thereby require the full game library and compatibility of all -17, -25 and MPU100/200 games.

Of course, I am a cheap bastard and would love to see a DIY PCB with the PLD, SMT parts already mounted and I can populate it with the 6800/6821s from stock or the old board it is replacing.

#28 2 years ago
Quoted from barakandl:

I am learning PCB software and have been kicking around the idea of a replacement MPU budget style. The BOM on a bally MPU setup like the altek is pretty damn low. I have successfully relaid out the -51 sound board that is in proto phase which gives me confidence I can do the Bally MPU.
For the -35 replacement with maybe mpu-200 support....
Do a 6802 cpu and crystal to eliminate that damn clock generator circuit and the 6810 RAM.
Pads for 6264/NVRAM in SMT SOIC-28 and DIP28 (i am not sure if i know how to make this compat with MPU200 and -35 ram setup).
Single EPROM 2764 or 27128
Resistor/cap networks to eliminates large numbers of discreet resistors/caps.
Assembling the boards would be the biggest issue unless i try and pay someone to do it for me. I am also thinking about offerning them as DIY assembly pcb kits that include the blank pcb and all the parts to assemble.

This would be cool.

#29 2 years ago

I'd like to see an MPU replacement for $50 or so. Being in Canada, I automatically pay 25% more, so $300 for a new board for a $700 is too much. Cheaper to just fix the old board.

#30 2 years ago
Quoted from barakandl:

I have gone through 1000+ of MC6802P used pulls and i can't recall more than once or twice a used pull had a good CPU but the internal RAM was bad.

I don't doubt that. They may have been tested before you got them. I've seen it happen a couple times where the RAM will fail in the 6802. It's not an epidemic or anything. I still trust the new RAM farther than the old and it doesn't cost me anything to configure it that way.

#31 2 years ago
Quoted from CactusJack:

Personally, I think the proper "re-design" of the Bally/Stern MPUs would be to eliminate the 6821 PIA and to use a PLD if possible.

That's something I've been working on. Either replacing the PIAs with CPLD or the CPU and PIAs with FPGA. It's not a difficult thing to do in theory because the VHDL for the CPU and PIAs are already out there. The hard part is making it cost effective. Until the PIAs become scarce, it's still a lot cheaper to just run with the 6821s.

#32 2 years ago

This thread has moved on a bit, but I figure I should post a conclusion of sorts anyway. Last night I had a chance to spend some time going over U11 in detail. Looking carefully under the socket, I could see many pins where there was no solder on the upper part of the board, and some pins where there was too much solder that could have been touching multiple tracks (it's pretty tight under there, lots of tracks run very close to the socket pins). So I spent quite a while doing something like pinhole surgery. Made sure that solder flowed through in all cases, and removing extra solder with solder wick. I didn't want to remove the socket, as the board was already looking a bit questionable, I was pretty sure that'd do more damage. Once I'd done that, I metered out every pin, and every other location that was supposed to have continuity, did some more tidying up, and then powered it up. I was still pretty amazed when I got six flashes (no 7th flash on the bench, 6 is good enough for me on these). Then, into a similar machine, though still with the Mata Hari ROMs, and off it went. It seemed pretty reliable, so I've given it back to Dave for a quick test in the real machine. My testing hasn't been thorough, so I won't be too surprised if it still has minor issues, but I think it's pretty much there. Finally...

Quoted from jwilson:

I'd like to see an MPU replacement for $50 or so. Being in Canada, I automatically pay 25% more, so $300 for a new board for a $700 is too much. Cheaper to just fix the old board.

Yep, being in New Zealand, the situation is the same here. Tax is lower, but shipping kills it too.

Quoted from CactusJack:

Personally, I think the proper "re-design" of the Bally/Stern MPUs would be to eliminate the 6821 PIA and to use a PLD if possible.

Definitely something I've pondered - do absolutely everything in a FPGA. Not too sure about implementing NVRAM in a FPGA, might need that to be external still.

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