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Looking for help: Mars God of War

Discussion in 'Pinball Tech Support' started by Moonveil, Jun 20, 2020.

  1. Moonveil

    Moonveil New Member

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    Location:
    St Thomas, Ontario
    Hi Everyone,

    I've got an old Mars God of War that I'm trying to bring back to life but could definitely use some direction. I got it 6 or so years ago back when I lived in Edmonton and it had been hacked up to the point there wasn't even a power cord left. I got as far as putting a Pascal board in and that got the game at least to the point you could play it.

    Fast forward a move across the country and when we initially set it up in Ontario it still played (as much as it ever has at least). Didn't last long though as it is now blowing the F6 8amp slo-blo 'solenoid/24VDC' fuse. I got frustrated and have put the machine aside for some time now but if I recall, it was either when the outhole, ball release or might have been the flipper solenoids went off that it blew F6. I had replaced all those coils though. Do they ever go bad just from sitting? I have the manual for the game and it lists resistance values there. Testing in place, the ball release and outhole both seem fine as do the lower resistance values for the flippers. (Am I right in assuming there's no way to check the the higher resistance coil on a flipper coil without pulling it?)

    Some other info I can think of from my snooping around the machine tonight:
    -The sound on the machine has never worked while I have owned the machine. The sound board is on the 24VDC portion of the F6 fuse circuit
    -I also noticed the F18 "RAMP" coil (I'm guessing they're referring to the stargate coil?) fuse is blown as well. I think this might have always been the case though as this ramp never worked while I've had the machine. This coil doesn't seem burnt or anything but also doesn't look great. I think it might be the only one I accidentally missed when I first replaced all the coils.
    -There's three large 2N5875 transistors under the playfield which I don't think I replaced. They serve the ball release, ramp and right launch lane.

    At this point, I think what I could really use some help with is putting together a shopping list of parts I should pick up for the machine. I could also really use some suggestions on how to tackle trying to get it alive again. Currently it spools up and goes in attract mode and the game will start (if I had the fuses) but as soon as it starts it blows right after.

    Currently I think this is my shopping list:
    -8 amp slo-blo fuses (F6 fuse)
    -2 amp slo-blo fuses (F18 fuse)
    -3x 2N5875 transistors
    -2x KBPC25-02 bridge rectifiers (might as well do the other one too?)
    -1x KBPC35-01 bridge rectifier (12vdc "power supply sound board". Might as well do them all, yeah? I have no idea how old they are. I already replaced the large orange capacitor)
    -2 pairs of flipper rebuild kits. (They don't feel very good, I'm fairly certain they need to be rebuilt.)
    -1x A-17875 ramp coil
    -1x A-20095 super flipper coil (why does the manual label A-20095 as 'super flipper' and A-17875 as 'flippers' when the only thing the A-17875 seems to be for is the stargate ramp?)

    Also, does anyone have some pictures of the right A-15838 kicker and fulcrum inside this machine?

    https://www.marcospecialties.com/pinball-parts/A-15838-GTB

    This assembly apart from the rollover switch has been yanked from the machine for some reason before I purchased it. You need this for the multiball so definitely something that I want to replace. On that note, does anyone have one of these laying around?

    Thanks for the help!
     
    #1
  2. sylvain

    sylvain Active Member

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    Re: Pascal board, is it only the MPU, or combining MPU/Driver/power supply?
    The MPU-Driver harness is also often problematic on those games, especially if the original MPU had battery corrosion that might have impacted pins inside the harness.

    I would recommend basic troubleshooting be performed first before preparing a parts shopping list, to find out the actual reason why the F6 8amp slo-blo 'solenoid/24VDC' fuse blows, and repair this first. Typically it is not because of a coil as such, at least initially, unless one is burned now due to prior overfusing. It is usually because a drive transistor on the Driver board is shorted, leaving the coil always on instead of only being pulsed. Such shorted drive transistor can easily be tested on-board, then replaced. There are good web sites out there showing how to test transistors with a DMM. Make sure any replacement coil is the proper coil number and has its diode installed at its lugs, and that the wires to the coil are connected with the correct orientation with regards to the orientation of the diode on the coil. Otherwise a new replacement drive transistor/fuse would short and blow the fuse again if the diode is missing or backwards. Also make sure not to overheat or leave the soldering iron on any coil lug for too long, as the attached diode might internally short circuit due to the excessively high temperature at its junction. The game manual should have wire colors and diode orientation to help.

    If the flippers use the same fuse (often not the case), check the game schematics to confirm - then check the End-of-Stroke switch under the playfield, e.g. to ensure the EOS switch opens when the flipper is in the 'up' position.

    Another issue with those games is the ground between the power supply, MPU and Driver board. A bad MPU-Driver harness (with poor/corroded pins) could lead to some drive transistors being 'half-on', causing heat then shorting the drive transistor(s). There are some good Web sites out there describing the problem and addressing it (Ground Mod on a Gottlieb System 80).

    Good luck!
    -Sylvain.
     
    #2
    Last edited: Jun 20, 2020
  3. Moonveil

    Moonveil New Member

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    Location:
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    Yeah it's the all in one board, the reviews I read about it praised it for the fact that it totally bypassed the grounding issue between boards that are common on the system 80's.

    I'm pretty sure I figured out the issue. Grabbed a couple fuses from the store so I could try and find the culprit. Ran the coil test on the machine and everything on that worked. I noticed the bottom left flipper though was stuck down. Pulled it up by hand so the end of stroke switch was opened and the low voltage then held it in place. I think it's more a mechanical issue, those flippers seem to have something holding them in place up until a certain point which I'm guessing is just a trait when they're worn out. Going to get my rebuild kits and a new solenoid for that stuck flipper just in case it got a little toasted.

    I double checked the diagrams to trace back the flippers and now that I have a Williams machine too... Williams manuals of that era are soooooo much easier to follow than Gottliebs. The flippers don't explicitly show the connection back to the F6 fuse that I'm blowing but the returns for the flippers to say they connect to switching 24VDC and the only 24 volt connection on the transformer is right at F6 so I guess that's that.
     
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