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Big Guns - Williams System 11 - random lock ups

Andy B

Site Supporter
Oct 6, 2014
Hull. England.
Brought Big Guns back to life.

However having reset problems.

Appear to be totally random. No rhyme nor reason. Most of the time it just locks down rather than resetting I.e. everything shuts down (including displays), blanking led goes out (though 5v led stays on) and you have to switch it off and on to get it working again.

It has a brand new Rotten Dog MPU board in (original was acid damaged beyond repair).

I have replaced all diodes on flipper coils. I have replaced all capacitors on power supply board. I have replaced BR on power supply board. Reflowed solder on power supply pins on power supply.

Doesn’t appear to be linked to how much is going on on the playfield. Sometimes it shuts down even just launching a ball.

It seems to get worse the longer you play it. I.e. you can play for about 5 mins with no issues. Then you get your first lock up/reset. Then it’s a couple of minutes to next one. Then a minute. Until eventually you’re getting a reset/lock up every game. Switch it off for a few hours, come back, you’re back to it playing fine for about 5 mins then resetting, couple of minutes to next one etc.

From time to time the score displays are going wonky too. Displaying gobbledegook. If I play a 4 player game. All scores are displaying fine then maybe Player one shows fine and two three and four show gobbledegook until Player two comes up then player one and two scores will display correct and when player three comes on players 1 - 3 scores show fine but 4 is still showing gobbledegook and the when player 4 starts playing all 4 displays show correctly.

I am at my wits end. I don’t really want to replace power supply board at £150 - and no one seems to have any in stock - particularly after all the components I’ve replaced on it already related to 5v.

I am wondering - The machine has been stored in a damp environment - though not wet - and the transformer casing is rusted to hell. How likely is it that that’s the culprit - that the AC voltage output from the transformer is unstable? I’ve never had a transformer go wonky on me before and have always been able to resolve Williams reset problems in past using No More Resets for WPC or replacing power supply on a Banzai Run I worked on (another system 11).
not likely to be the transformer. more likely the power supply. or the mpu board.
That’s what I thought.

MPU is brand new though.

I think I’ll just bite the bullet and replace the power supply board.
Agree with @AlanJ

Also it could be connectors. If you put rubbish connectors onto a new board it is still a rubbish connection!
They all look surprisingly good and there are no tell tale, acid creep, green pins. All damage on boards was South of batteries and I couldn’t see that it had gone more than about 30mm and nowhere no connectors up or down.
They all look surprisingly good and there are no tell tale, acid creep, green pins. All damage on boards was South of batteries and I couldn’t see that it had gone more than about 30mm and nowhere no connectors up or down.
Get someone to play it and have a little wiggle of the cables :)
If the time between it happening decreases each time it sounds heat related, see are any components hot after it's happened
With power off check all fuse holders in the game, the ones on the PSU are notorious for being fragile.

Keep a meter to hand. The next time it dies, leave the game switched on and measure the voltage on the PSU or AUX board.

My guess is either a faulty cap or BR on the PSU but it could be elsewhere in the game pulling down the power supply but you need to know where this is happening to begin the process of rectifying it.

As previously mentioned dodgy connectors (and old wiring) can be a big problem on these games, even just wiggling a wiring loom might cause or rectify issues (done just by opening the backbox light panel for example).

One other thought is to leave the game running in test mode, just continually operating coils and flashers to see if one of those is causing the problem (should be repeatable). It could be a coil short which only happens once the coil is suitably warm to expand a little and short itself.
One of the resets today restored the MPU to factory and I had to adjust to free play again.

One blew F4 on Aux board 2A slo-blo 50v dc coil.

I have measured the voltages on the test boards. Bear in mind this is a Rotten Dog replacement so I guess the TPs could be different from factory.

TP1 5v = 5.16 in attract mode. 5.16 game started ball in shooter lane. 5.18 immediately after a lock down.

TP2 18v = 16.56 to 16.71 in attract. 17.4 to 18.01 game started ball in shooter lane. 17.56 after a lock down.

TP3 Reset = 5.02 to 5.07 in all states

TP4 Blanking = 5.16 in attract and game started. 0 after lock down (blanking LED off as well).

TP5 IRQ = 4.97 in all states.

Voltages all test good on Power Supply board test points.
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Had the Aux Power Board out last night checking diodes. Played it for a few mins this morning and everything working fine until about minute 3 then displays started to go wonky every few balls. Random gobledeegook. Then scores were not advancing all the time. Then finally it shut down on me and a switch off and switch back on again sorted it.

I've never had this thing fully working yet without the resets but I did swap out the old flipper switches which were old and knackered. There are a couple of ceramic disc capacitors on each flipper switch stack and I wondered if maybe one of these could be faulty and maybe leaking some of the HV back? I did a continuity test on the capacitors on each flipper switch and am getting different results on the left switch stack than the right.

Best way I can describe it is; When switch leaf 1 is the long one nearest the button, 2 is the middle one and 3 is the furthest from the button. Each switch has a capacitor leg connected to switch 1 with the other leg of that capacitor connected to switch 2 and then another capacitor connected from switch 2 to switch 3:

Right side I get continuity from the leg on the capacitor on switch 1 to every leg of each capacitor through to switch 3.
Left side I get continuity from leg of capacitor on switch 1 to leg of capacitor on switch 3 (but guessing this could be via wiring). I get continuity of capacitor leg on switch 2 and 3 (same capacitor). I DO NOT get continuity form leg of capacitor on switch 1 to leg connected to switch 2 (same capacitor).

I am guessing that this is an unreliable way of testing and I need to take each one out but I would have thought that as both flipper buttons do the same thing then continuity results should be the same or am I oversimplifying it?


I noticed that whenever I got the resets there seemed to be something going on with the displays (garbled rather than not working) too.

I know they are on different circuits on power supply board but wondering if this hack on back of display board could be causing resets issue? Couple of resistors soldered on with some kind of leg extensions soldered on the resistors so they bridge the gap between the solder points on the board.

I’m thinking if these resistors are out of spec maybe this is putting strain on the feed to the power supply generally and so diminishing/robbing the feed to the +5v as too much being fed to displays? Aren’t the 5v on some boards fed from voltages elsewhere?

Apologies for the non-tech terms!


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Update - 28th September 2023

Well, I don't like to do this and I've never done it before but I am admitting defeat with this one.

I bought a new RD Power Supply Board for it. Same issues with random lock ups (I'm describing them as lock ups rather than resets now as everything freezes, displays go off, lamps lock on, solenoids stop working, sound dies and only way to free it is to switch off and on again - it doesn't start a new game like a reset would do).

I disconnected displays. Same issue with random lock ups.

I disconnected sound board. Same issue with random lock ups.

I disconnected Aux Power Board. Same issue with random lock ups.

One of the times it locked up the knocker fired so I disconnected that (getting desperate or what!). Same issue with random lock ups.

I replaced power connector on MPU coming from power supply board to MPU board. Same issue with random lock ups.

These lock ups will occur during attract mode as well as during play and at random times though more often than not after the machine has been switched on for say half an hour.

Switching the machine off and switching it back on clears the lock up.

You can get a half hour or more of multiple player games, play, all guns blazing (excuse the pun) with flashers, solenoids, flippers, all working, multi-ball - everything with no issues - and then it will just freeze for no apparent reason. You can play it, go away, leave it in attract mode, go back to it multiple times and it will be fine and then it just locks up in attract mode. You can switch it on, not play a game, just leave it in attract mode and it can lock up after 10 mins, half an hour but eventually it always locks up.

A few times it has locked up, when I have switched it back on it has come up with a "Factory Setting" message and I have to set to free play again - it has a new RD MPU board in it so doesn't require batteries so totally stumped as to why it would forget settings after locking up.

Anyways unless anyone's got any lightbulb moment suggestions for what I might try next I'll be listing for sale later tonight.

Gutted since as my objective with this one was just to bring it back from the dead, get it working again and sell it on for what I paid for it or maybe take a little hit, just for the challenge and so someone could have a playable machine for reasonable money which they could do up cosmetically. Now it looks like I'll be taking a big hit on it but needs must, money has to be put back in bank account missus says :-(
One last thing. When I disconnected sound board last night I was able to play it for ages before it eventually locked up when I left it in attract mode.

When it first switches on it makes a loud screeching sound (best I can describe it).

Turned volume up on it this afternoon (trying anything now) and the sound “undulates” in time to the lights flashing. You can hear this at relatively low volumes also.

I don’t think it’s a sound issue that could be causing the lock ups (I believe sound board shares 5volts with MPU board via looped grey wire) since as I disconnected power from sound board and it still locked up last night but it doesn’t sound right at higher volumes so wondering if there could be any kind of connection.

Video uploaded so you can see (and more importantly hear) what I mean.


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what happens if unplug sound board completely so it’s not connected to anything at all
That’s what I did last night.

Removed all connections from soundboard.

But I did not remove soundboard connections from MPU rather removed at the soundboard end if that makes sense.
One more go before I PM Phil and tell him to have it off me 😊

Under playfield back of cab. Board - which I suspect to be interconnect board mentioned in repair guide - see photo. This board is not mentioned in manual and I cannot see it in wiring diagrams.

It looks scabby - as I said machine has been stored in damp environment so there’s rust etc down there.

2 connectors down left side hooked up. 3 down right side. Resistors spanning the gaps. Would have thought there would be 3 down one side 3 down t’other? Anyways I have no spare connectors hanging loose!

Some of those ceramic resistors look a bit suspect but none of them have any values on them and like I say, I don’t see the board in the schematics and repair guide says different value resistors are used depending on how many flasher are wired in a circuit. Flasher bulbs are 12v right (thinking about Alan’s comment above)? But repair guide says 12v for flashers comes from 28v coil voltage limited by those resistors so that wouldn’t disrupt the 12v supply would it?


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I looked at a schematic, and actually not much on the 12V - so probably a red herring as you have replaced the PSU, so the 12v should be solid.
I looked at a schematic, and actually not much on the 12V - so probably a red herring as you have replaced the PSU, so the 12v should be solid.
Cheers Alan - been chasing a lot of red herrings on this one 😊

I bet it’s something stupid like a dodgey connector or something.

Playing it last night and a bunch of flashers were not working. Reseated connector a few times and hey presto all working fine again!
I once had a load of fun with a Rottendog MPU4 in a Sega Maverick pinball, rare random resets and no memory saving at all. The board had an STK12C68 nvRam installed but seemed to be an early revision PCB and not wired correctly for that particular chip, it seemed like it was wired for the 62256. Can't remember exactly what the modifications were but I cut a couple of traces, added a capacitor and jumpered some wires to fix the issue.

Found there were others posting about issues with Rottendog boards and the memory backup system on Pinside, so there's a bit of strangeness going on out there!
mpu resets if the +12v unreg drops below 10.5v according to sys11 manual

I noticed that the 2 x 3 bank drop targets at the top of the playfield seemed to randomly fire occasionally.

I was thinking maybe switches falsely registering as shut or not registering when in down position. Probably unconnected to reset issue I thought but looked in to it none the less.

Didn’t realize the switches for those were optos (thought this game was pre-optos).

Checked power wiring diagram and it looks like power to those two opto boards is +12V unregulated.

So I have disconnected all connections to the pcb boards for the 2 x 3 bank drop targets and left it in attract mode and it's been absolutely fine for 3 hours now.

Haven't played a game yet - too scared - you know how disappointing it is when you think it's all sorted and the issue comes back - but am gonna leave it a few more hours in attract mode and give it a pop later.

Maybe another red herring but who knows.
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