Gottlieb Sys3/Stargate help - coil locking on.

Frax

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Okay, I just replaced Q4, which is the driver for the right sling. It was locking on as soon as you start a game. After putting the fuse back in and starting the game, it did NOT lock on, but after a few ball strikes it DID.

What gives? I'm about to pull this coil and replace the diode and meter it out, is that the likely culprit here, a bad coil? I don't have a Stargate manual or schematics. As far as I can tell, I don't see any pre-driver transistors/MOSFETs for these coils, but I tested every other MOSFET on the board and none of them were bad prevously, so if there is one....not sure why it would be causing an issue at this point.

I'm really in the dark with this kind of repair, it's the first time I've done PCB work at all, my soldering looked excellent though. :p
 
Honestly, I didn't try. It locked up when I tried it in an active game, I turned it off and pulled the half-burned fuse. It locked on the third fire, and it wasn't really rapid repeats...it was like

Fire.....one second. Fire...second and a half. Fire, LOCK. "OH SH..." *turned off*

I haven't pulled the coil yet, won't get to it until tomorrow. Bah.
 
Here's the relevant piece of schematic:
attachment.php


"Pre-driver" "decoder" or whatever controlling Q4 is the 74HC273 at U1.

A coil doesn't 'lock on' because the coil is bad - but - a coil will burn if 'locked on' long enough.
 

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    driver3.JPG
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Thanks for that. I don't have a logic probe or scope so probably not going to bother trying to troubleshoot that part. Frankly, if it's locking on because of that U1 chip, I'm just going to sell the machine as-is and be done with it. Replacing those things is way beyond my experience and I'm not going to the hassle of learning it for a machine I'm probably not keeping anyways. :|
 
You can send the boards out to have them repaired to a number of places...

A lot of time coils appear to lock on because of stuck switches. When I bought my stargate I had like 6 stuck switches I had to adjust (rebend) to get the coils to turn off.

Put it in switch test mode and start looking.
 
Switch test not showing anything abnormal for the record. Just that the glider is in resting position and the balls in the trough. :/

Also checked the switches on the sling itself last night and they aren't stuck shut or shorted on anything.
 
It doesn't really sound like U1. If U1 was the problem then replacing Q4 probably would not have fixed it for the short time it did. Now that it locked back on again, does it lock on as soon as you start a game now? Or does shutting the game off and restarting fix it for a few cycles again. If restarting fixes it for a few cycles then it locks in mid-game, it probably is U1,

If not U1 and replacing Q4 fixes it until the solenoid gets activated a couple of times, check D4. If D4 is open, or has a connection problem causing an open, the inductive spike generated when the coil turns off may be killing/shorting the MOSFET.

Have a very close look at the wiring, if coil control circuit is shorting to coil power anywhere it will keep taking out Q4, vibrations from the coil energizing could even be causing something that is too close to touch.

It's possible that the coil has shorted turns and is causing high current flow in the circuit. That would be a very rare failure, but if all else checks out could be worth looking into.

Good luck,
D
 
I put the fuse back in to look at it. It's now back to locking on soon as a game starts. In addition, with the fuse there but NOT blown, you can't use the flippers to navigate the test menu?
 
did you replace the diode across the coil? a cracked diode will do just this!

That was the next plan of action in my list, I just haven't gotten to it. Problem is with the coil locking on again, I've gotta pull the stupid driver board, put in another MOSFET too, so it's like double the work just to check and see if it will work at all. I guess technically, I could just go clip the diode and leave it if that's not it since the fuse is ou...........

Nah...that's just asking for trouble. BAD FRAX.
 
Took it apart, and the diode is wired BACKWARDS from how the opposing coil is wired...I'm guessing that might be part of the problem. Derp. More specfically, the coil is wired backward. That's the same thing I did on Pinbot with the flipper coil. Pretty much the same effect...only it killed the fuse before it killed the driver, whereas stargate is killing the driver BEFORE the fuse!

Meanwhile, the damn bracket fell apart on me!


Untitled by Fraxcat, on Flickr

FUUUUUUUUUUUUUUU......
 
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After fighting with it all night, I have emerged..


VICTORIOUS!

In the end, it turned out that it WAS wired right (I had to learn how to read Gottlieb wiring diagram and color numbers!), that the diode that was on the coil was NOT bad (whoops!) and that it was in fact...

Broken off the lug. Dammit! Found out when I was playing with my multimeter, touched it, and it pushed right off. It was sitting on there so perfectly I couldn't have told visually without a magnifier or something that it was broken. It wasn't jiggling around at all while I was removing the coil.

But yes, the MOSFET was thoroughly fried, and I killed two more in the process of learning everything, along with 3 fuses. But a fun learning experience overall, my first PCB repair ever and I didn't completely f-up a trace or through hole! I really need a finer tip soldering appliance though. The fat poker tip that came with it is a bit hefty for board work. I learned to love my solderpult or whatever it's called. Very handy.
 
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