(Topic ID: 233137)

williams system 4 briefly firing all controlled coils at power up


By creepykenny

5 months ago



Topic Stats

  • 19 posts
  • 6 Pinsiders participating
  • Latest reply 4 months ago by Atari_Daze
  • Topic is favorited by 2 Pinsiders

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    #1 5 months ago

    williams system 4 phoenix machine

    so, dragging this one back from the grave and now have it up and running mostly correctly but still a nagging issue, when the power switch is turned on, all of the controlled coils fire for a split second and then the MPU boots and all is normal - none of them are stuck on. i am not that familiar with the intricacies of a system 4 machine but i don't believe this is normal behavior

    i am assuming it may be a blanking issue of some sort, so monitoring the PIA at position 18 pin 4 there is pulsing activity, pin 19 on same PIA goes from nothing straight to high with no pulsing at power on

    timer 556 pins 9 & 13 are both high no pulsing

    i feel like i am missing the initial low signal that would prevent these coils from firing at power on

    or am i?

    #2 5 months ago
    Quoted from creepykenny:

    i feel like i am missing the initial low signal that would prevent these coils from firing at power on

    I'd check where the blanking comes into the driver board after the interconnect, make sure it's toggling at power up correctly. If not, trace it back

    #3 5 months ago

    thanks! i have done that, the blanking signal (high) is present on the driver board - monitoring pin 37 of the interconnect with a logic probe shows on power up signal transitions from zero/nil straight to a steady high - no low signal is present on the driver board

    the coils are firing before the high signal appears - while there is no signal being sent from the MPU, so am i missing a constant low on the blanking line that should be present when power is turned on before MPU boots?
    i feel like i am, and with out the low signal the coils are firing .. since if i understand how it works a low signal on the blanking line prevents the coils from firing?

    i could easily be wrong tho

    #4 5 months ago

    Interesting, I'll be watching this topic to see what may come of it as I had something similar caused by my own hand but is still a mystery!

    https://pinside.com/pinball/forum/topic/can-you-smell-what-atari_daze-is-cookin-or-who-let-the-smoke-out

    #5 5 months ago

    I'd probably start by just replacing IC23 if you have one handy.

    #6 5 months ago
    Quoted from creepykenny:

    thanks! i have done that, the blanking signal (high) is present on the driver board - monitoring pin 37 of the interconnect with a logic probe shows on power up signal transitions from zero/nil straight to a steady high - no low signal is present on the driver board
    the coils are firing before the high signal appears - while there is no signal being sent from the MPU, so am i missing a constant low on the blanking line that should be present when power is turned on before MPU boots?
    i feel like i am, and with out the low signal the coils are firing .. since if i understand how it works a low signal on the blanking line prevents the coils from firing?
    i could easily be wrong tho

    This could very well be a case of the indeterminate nature of inputs not turning on in a known state - (like the Gottlieb system 80 thunk on powerup, or WPC thunk on turnon)

    There's always going to be this type of state on power up until the power is stabilized, unless some kind of separate reset timing type circuit is added (as in, no power to the coils until the power is stable.... something along those lines).

    FWIW a couple of my system 4-6 games do this as well. I'm kind of used to it.

    #7 5 months ago

    i do have a spare 556 so a swap is not a problem and thats what i will probably do just to see if it is at fault, without pulling it and putting it in a tester i don't know how to verify its out puts when its used on this board so theres that.

    as for the power up state ... well this is what i am really asking, is there a (or is there supposed to be a) low signal present upon power up on the blanking line and what generates it? the 556? it would have to be instant low to effect blanking the coils before the mpu boots and changes its state to high

    maybe its the nature of the system 3-6, haven't seen other posts about this "issue" but my googlefoo kinds sucks

    #8 5 months ago
    Quoted from creepykenny:

    i do have a spare 556 so a swap is not a problem and thats what i will probably do just to see if it is at fault, without pulling it and putting it in a tester i don't know how to verify its out puts when its used on this board so theres that.
    as for the power up state ... well this is what i am really asking, is there a (or is there supposed to be a) low signal present upon power up on the blanking line and what generates it? the 556? it would have to be instant low to effect blanking the coils before the mpu boots and changes its state to high
    maybe its the nature of the system 3-6, haven't seen other posts about this "issue" but my googlefoo kinds sucks

    By my understanding part of the point of the blanking is to kill the outputs until the CPU boots, but I don't have a board handy. None of the sys3-7 games I've owned ever made a thunk though

    #9 5 months ago
    Quoted from zacaj:

    By my understanding part of the point of the blanking is to kill the outputs until the CPU boots, but I don't have a board handy. None of the sys3-7 games I've owned ever made a thunk though

    this is my understanding as well, otherwise whats the blanking point? .... will pull the 556, socket its replacement and post results

    #10 5 months ago
    Quoted from creepykenny:

    otherwise whats the blanking point?

    The other point of it is that if the CPU locks up, it'll kill the solenoids and displays before they burn

    #11 5 months ago
    Quoted from creepykenny:

    i do have a spare 556 so a swap is not a problem and thats what i will probably do just to see if it is at fault, without pulling it and putting it in a tester i don't know how to verify its out puts when its used on this board so theres that.
    as for the power up state ... well this is what i am really asking, is there a (or is there supposed to be a) low signal present upon power up on the blanking line and what generates it? the 556? it would have to be instant low to effect blanking the coils before the mpu boots and changes its state to high
    maybe its the nature of the system 3-6, haven't seen other posts about this "issue" but my googlefoo kinds sucks

    Nothing generates the low signal. You can't have control over a semiconductor until the voltage is up and stable. Unless there is something in there like a reset/supervisor IC that specifically blocks the output path, the power up is going to create an unknown state until it is stable enough to exert control.

    They just didn't think it was a big enough deal way back when - it's relatively harmless because it's so short. There could probably be some kind of adapter made to go onto the solenoid grounds that has a separate power on just like was done for the AMP on the WPC era machines.

    How much of a thunk are you getting - it should be VERY short.

    The main purpose of blanking is to actually blank the displays during display refresh (that's why it's called 'blanking'.....) - as a nice side note, it's also supposed to safe the lamp and solenoid matrix in the case of interrupts being missed (Generated by 555/556 timer on system 3-7) - in practice, it does not always do this. There is not a separate watchdog circuit that would be the correct way of doing this.

    You could have an error on a machine where the software is not running in its proper state, but the interrupts will still plug away happily. For instance, good OS rom but bad game rom. Wms doesn't checksum at bootup, only when you press test button.

    #12 5 months ago
    Quoted from creepykenny:as for the power up state ... well this is what i am really asking, is there a (or is there supposed to be a) low signal present upon power up on the blanking line and what generates it? the 556? it would have to be instant low to effect blanking the coils before the mpu boots and changes its state to high

    I tested my Black Knight since I happened to have it open. Pin 37 is low for a good quarter second or more before going high.

    Quoted from slochar:

    The main purpose of blanking is to actually blank the displays during display refresh (that's why it's called 'blanking'.....) - as a nice side note, it's also supposed to safe the lamp and solenoid matrix in the case of interrupts being missed (Generated by 555/556 timer on system 3-7) - in practice, it does not always do this. There is not a separate watchdog circuit that would be the correct way of doing this.

    Blanking doesn't blank the displays during the refresh on sys3-7. It should stay high during the entirety of normal operation according to the manual.

    I put a logic probe on it, there's no pulsing.

    #13 5 months ago

    I'm thinking Bally world then - I thought the blanking worked the same way on williams. There is a blanking signal going to the display board but obviously, it's just for watchdog and not actually performing the blanking.

    For the OP, had a thought - are the board grounded with all the screws present? If your ground was floating slightly on your transistors that could certainly cause some issues.

    #14 5 months ago

    OK, originally every controlled coil (8 total i think) briefly fired at power up every time i turned the machine on, initial plan was to pull the 556 -test and replace if bad, thought it over alot & honestly not convinced thats the actual fault but it could well be, in lieu of pulling the timer i/c i spent yesterday going thru all of the drop target assemblies cleaning those little pcbs & applying some nice new decals provided by the owner to the targets, once done i turned the machine on same as always and now none of the controlled coils fired like before - totally silent

    grab logic probe and apply it to pin 37 on the driver interconnect, power machine on and all coils fire same as before (signal transitions from nothing to high same as before) , power on with out the logic probe on pin 37 and coils are silent again

    all grounding screws are present on both mpu & driver boards

    need to probe the 7408 inputs but starting to think broken solder, damaged trace, bad connection or a flaky i/c somewheres although everything works correctly once we get past the mpu boot blanking going high

    #15 5 months ago

    I'd replace C31, Q5, and IC23 and *hopefully* be done with it. Any/all of those 3 can cause the coils to fire upon boot-up. I had a very similar problem with my Black Knight a while back, but it was activating all the coils *and* blowing the 2.5A slo-blo coil fuse upon boot-up...but it was only doing it intermittently...and if it managed to boot without blowing the fuse, it would work perfectly fine for hours on end. Drove me nuts. Still can't remember how i came across the suggestion to replace those components for the blanking circuit, but that fixed it and has worked fine ever since. They're easy enough parts to replace, and if they don't fix it at least you know you have a good blanking circuit for the foreseeable future.

    Here's the relevant portion of Clay's guide that i got the info from:

    Likely Blanking Signal Problem Parts.
    Remember the likely cause for a low blanking signal (other than the things mentioned above) is a timer chip failure (556 for s36, 555 for s7) at IC23, a bad C31 (1mfd 25v polarized) capacitor, or a bad Q5 transistor (2N4403). The Q5 transistor tests easily with a DMM, and replace cap C31. The timer chip is small and cheap to replace. So start with those thing. In system3 and system4, the 556 timer is also used to generate the IRQ signal, so suspect a bad C31 or Q5 first. On System 6/7, the timer chip (556 for sys6 or 555 for sys7) is only used for blanking. Also on sys6-7 look at the outputs of IC25 (4020 1ms timer) with a scope or logic probe. If the interrupt signal is not being generated at the correct speed, then 555/556 timer IC23 will not generate the required "pulse".

    #16 5 months ago

    OK, sounds like good advice, i have everything on hand except the capacitor and i may have one of them and just not know it yet will have to dig around and see

    thanks!

    #17 5 months ago
    Quoted from zacaj:

    I tested my Black Knight since I happened to have it open. Pin 37 is low for a good quarter second or more before going high.

    Blanking doesn't blank the displays during the refresh on sys3-7. It should stay high during the entirety of normal operation according to the manual.
    I put a logic probe on it, there's no pulsing.

    Correct. The Blanking circuit watches for regular pulses from PA2 on PIA1 (Displays). If the displays aren't being updated the blanking circuit assumes that the CPU has crashed and therefore drops the blanking signal to LOW.

    Code is not executed on the CPU until after the reset cycle, and once running it will take a few more cycles to fully initialize the PIA chips. It's possible the PIA's may be putting out the wrong signals during this time.

    You could pull the GAME2 ROM to prevent the CPU from doing anything at all after the RESET. Power up and keep your finger on the power switch and see if the coils fire longer, or indefinately, or even at all. Of course, if they do stay on, kill the power to prevent overheating and/or possible damage etc.

    EDIT: The above is what I learned from System 6 boards. I am assuming this particular aspect of Williams boards also holds true for Systems 3-7 since they are in the same family.

    2 weeks later
    #18 4 months ago

    i finally replaced the dual timer 556 & the 4403, did not have 1uf tant on hand so i did not replace C-31 just yet, but so far so good - none of the controlled coils are firing during initial power on and this is after many, many tries

    prolly pick up some of those tants on my next digikey order and replace it some times later

    so i'd say i am almost done or mostly done with it

    #19 4 months ago
    Quoted from creepykenny:

    i finally replaced the dual timer 556 & the 4403, did not have 1uf tant on hand so i did not replace C-31 just yet, but so far so good - none of the controlled coils are firing during initial power on

    Hmm, I've got some of these, may try it on my OE board for Laser Ball while my potential buyer and I await a shipping quote from Fastenal. It's been a week!

    Thanks for the update Kenny.

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