My Gottlieb Close Encounters is playing perfectly, but makes a heck of a racket at power up. If the power has been off for more than about 3 minutes, then when I turn the power on SLAM BANG all the solenoids fire at once, the game goes into tilt, and the credit button doesn't do anything. If I turn the power off and back on it boots normally (and quietly), and everything is fine. If I turn the power off for less than 2 minutes, then when I power it back on everything is normal. It only does this crazy thing if the power has been off for more than about 3 minutes.

This game already had the battery removed from the Control Board when I bought it. I wanted to install the RAM backup battery for high score memory, etc., so I added a remote 3-AAA battery pack (with blocking diode). This SLAM BANG issue didn't start until I hooked up the batteries. I did some experimenting...

If I only install 2 batteries (approx. 3V) the same thing happens.
If I only install 1 battery (approx. 1.5V) everything seems to work fine. What's going on? Is this the solution to the problem? The literature shows the battery is supposed to be 3.6V.

The slam switches are closed as required.
The power supply has all new caps and voltages are correct.
All grounding mods have been done.
Diodes (7) have been added in harness between Control Board and Driver Board.

Yes, when I used 2 or 3 batteries they were in series. Picture shows where I hooked up the batteries. Schematic shows what I tried. You say if I use one or two batteries that will not work. I am here to tell you that when I used 2 or 3 batteries it did not work. It only works with I use one battery. I can live with this as a permanent solution because it is working, but I don't understand why?

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Look at my pictorial schematic. Not sure how to show how I wired up the batteries any simpler than that.

That's worth a try. I'll change the caps.

I haven't changed any caps on the control board (yet). I have one battery w/ blocking diode (1N4004) hooked up to the board and EVERYTHING works fine. RAM is saving high scores and audits, and at power on everything is quiet....just like it's supposed to be. I measured the voltage drop as follows:
Power off, voltage at battery (before diode) 1.6V
Power off, voltage at control board, 1.36V
Power on, voltage at battery, 1.6V (the diode is working).
Power on, voltage at control board, 4.36V
So there is 0.240V drop across the diode, and the 4.36V with power on looks right (I'm assuming).

Again, if I hook up 2 or 3 batteries, the power on event is scary.

I don't know, I'm inclined to just leave all alone and use one battery rather than chase an unknown. I guess I'm looking for some definitive answer to what is going on.

Quench, that's all very interesting. So what would be your repair recommendation? Thanks for your input.

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Across CR37, 0.6V
Across CR38, 3.45V
Q5, E=4.3, C=4.25, B=3.49
Z2 pin 4 and 11 both 4.25V

I do have a logic probe. The solenoids do not lock on. It is momentary.

I just finished changing out C31 and C32. No change.

I don't think my probe has a memory function. Before I touch the probe to the pin 6 the green and amber LEDs are on. When I touch pin 6 the green LED on the probe goes out, the pulse amber stays on steady. When I power on the game nothing on the probe changes.

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Results: I checked the Z2 output pins when the game starts up with the bang. And I checked them before my 2 minute wait, so I would have a normal boot up. Checked with latch on and with latch off. Pin 6 does not flicker or show pulse at power up/down under any circumstance. Same with pins 7 or 9. No change of state upon power up/down. Pin 10 flicker pulse at power on, sometimes. These results are the same with or without a normal boot.

There is no corrosion around Z2.

I looked at the reset circuit mods provided by Tuukka. It appears I have the newer board, however I checked the resistors (did not remove from the board) and one of them (R159) isn't according to the mod literature. In the circuit I have 2.7M which is what I measured. The mod calls for 3.9M.
I measured as follows:
R159 = 2.7M
R160 is missing
R161 = 43k
R162 = 2.0k
R163 = 6.7k

I'm going to guess the recommendation is replace Z2 because there appears to be no activity at the outputs as expected, right? If this is the case, I have a question. Why does there also appear no activity when I get a normal boot? Should I replace R159 with 3.9M?

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I appreciate all the help and comments. I hope I'm answering/doing the logic probe correctly.

The 5V trimpot on the power supply was causing a problems early on. I cleaned it, as well as replaced all the electrolytic caps early on. Also replaced a few other parts on the power supply. I have all correct voltages to and from the power supply. That was last week. After all that, I was able to boot up the game for the first time. When I connected the 3 batteries for the board memory functions, that's when I first noticed this BANG on power up. Without the batteries, everything is normal, except I don't have my high score, audits, etc. If I only use one battery, everything is normal too (have all memory functions)...except that it's only one battery!

Probe to pin 8, both amber (pulse) and green (level) LED's go out.
Probe to pin 16, the green is on, and the amber is off.

Probing with power turned off:
Pin 6 green LED off
Pin 7 green LED on
Pin 9 green LED on
pin 10 green LED off.

When the game is powered on, all the outputs are the same except pin 9. It has changed to off.

Just to confirm I rechecked and MY MISTAKE. Pin 9 is logic high (LED on) both with the game is off and when powered on.

OK...I will be ordering some parts. Guess this thread will be on hold for a while. Thanks again.

I found a Z2 locally and replaced my bad one. I have 3 batteries in the battery holder. Yippee there is no more loud bang on power up, but OMG now I have another problem that I didn't have before. When I power up now (if the game has been off for a while), the displays, including the 4 digit status display, all show zeros. I can start a game but the scores show zeros. If I power off and back on, then everything is normal. Does this sound like a bad connection somewhere, or something on the board?

Not sure how to describe this....in test mode, the zeros kinda fade like I can almost see the digits change, but can't really. They look like zeros, but I can see a change each time I press the white toggle button in the coin door. Just not enough of a change to make out anything but zeros.

I can even start a game, just the digits are zeros.

I am not losing data. If I power off and back on, everything is normal and my data is still in memory. This only happens if the game has been powered off for a few minutes.

I don't believe it is slam tilt. Slam tilt is all zeros immediately at power on. But in my case, there is no display for about 5 seconds, like a normal boot. Then the zeros appear. And as I stated earlier, I can even play a game, just can't see the correct digits or status. It's a normal boot except for the display. Yes I have a ball in the game.

The weird thing about this is that it is similar to before I replaced Z2, in that if I power off then back on within a minute or so, everything is normal. This phenomena doesn't happen on the second boot....only on the first boot after the game has sat a few minutes or longer. Before changing Z2 it was the slam/bang. Now its the display zeros thing.

I have rechecked the side connectors at the MPU that go to the displays. They are all ok.

I replaced all the power supply electrolytics, including C1, a week ago. I suppose I could have a bad new cap....would seem unlikely, but possible. I don't have any way to check the cap. I guess I'll just go buy another one.

Meanwhile, I removed the new C1 and installed the old one. The slam/bang is back. Oh boy.

So plan now is to order a new C1. Waiting for parts.