System 11 Stuck Coil, Please help.

[Santoro]

The lower pop bumper on my Space Station is stuck on.  Following the guides (http://www.pinrepair.com/sys11/index2.htm) I replaced the coil, two transistors, and the two ICs behind them to no avail.  It still goes down as soon as the pin is powered on.

I am running out of ideas.  How can I troubleshoot this the next step? 

I took the offending coil out of the circuit and the other two bumpers work fine so I think I did a good job on the component replacements.  Could this be a switch problem?   Power?

The bumper first got stuck when I (very noobishly) tried to adjust the leaf switch one time while the machine was on.  I shorted something out and the rest is history.

[smartbomb2084]

So... You replaced the coil, Q79, Q78, U50, and U49? 

[Santoro]

I replaced the coil, Q78, Q79, U50 and U51.  I also replaced C74 (just in case) and R108 (it didn't test out at the right resistance.)

You thnk I should have replaced U49, and not the U51 PIO?  Maybe I replaced the wrong IC in error?  I don't think so, but you never know.

[Santoro]

reading it again and look at that:

Special Solenoid Logic Flow.
For Special Solenoids (SSa to SSf), here is the logic flow. This is useful to know if you are having a problem with a special solenoid.


SSx:    6821 PIA    7407    7402   2N4401    TIP122
---------------------------------------------------
...
....
....
....
....
SSf:  U54 (pin 39) to U49  to U50  to Q78    to Q79

Off to replace U49.  Thanks for the lead.

[lilshawn]

remember... all the solenoids have power 100% of the time...what happens when it comes time to fire them is the circuit to ground is completed...

the first thing the computer sees is the switch for the popper close... go to the switch test and see if it's stuck on and that it does indeed operate properly. if it is fine, the next thing that happens is the computer ends a signal to a chip which in turn switches on a transistor, that switches another larger transistor which completes the power loop from the solenoid to ground. since you've replaced the chip and transistors I would look for a wire thats grounded or pinched to the frame someplace.

you can check by disconnecting the offending solenoids return wire from the board. what this will do is isolate the power wire and the coil and it's return... if it is indeed shorted someplace along the return the solenoid will still come on. if it does not, perhaps you have replaced the wrong transistor... i've done it before.    

EDIT: read the new posts...  i'm too long winded

[smartbomb2084]

Had a similar problem on an EARTHSHAKER and U49 was fried alongh with U50.

I'll bet pin 12 of U49 is shorted (output F)

[Santoro]

U49 did not do the trick.  Investigating shorts now. 

I have found that BOTH sides of the pop bumper trigger leaf are grounded even when the machine is off.  None of the working bumper switches are like that.  Could this be caused by a bad diode or capaciter on the switch?

[Santoro]

you can check by disconnecting the offending solenoids return wire from the board. what this will do is isolate the power wire and the coil and it's return... if it is indeed shorted someplace along the return the solenoid will still come on.

So I did this.  The coil is not locked down when the return is diconnected from the CPU board.  If I short it to ground it fires.  This means i do not have a short the way I understand it.

if it does not, perhaps you have replaced the wrong transistor... i've done it before.

I have quadruple-checked this, it's the right one.  I am certain this is related to the switch problem I found.  Thinking back to how this happened, if I shorted the leaf switch somehow could that have fed back and caused a pernanent short somewhere unusual on the CPU board switch circuitry?  I need to pore over the schematics to see where the switch wire goes to on the CPU board and check components there.  Leave it to me to have a stuck bumper that is different from 99% of the other causes out there.   

[Santoro]

I was right, found a bad diode right where the bumper switch comes into the CPU board.  The diode is permantly closed to ground.  Off to fix that.

[Santoro]

Still no good after replacing the diode.  The only thing left to replace in this circuit is the SR20 resistor network, and I just found out that the section of that connected to this circuit is hosed too.  When I shorted this thing out last year I must have horked every component along the way. 

I need to order a resistor network, so I am done for a few days.   Thanks for all the help.

[shardian]

I've re-read all of your replies, and it appears you haven't ruled out a physically stuck switch. If your apron is worn or dirty, it can get stuck in the switch cup and cause the coil to lock on. Replacing the aprons is a good idea with special solenoid era pins. They're only a 30 cent part.

Also, make sure you have the proper rated fuse installed for the coils.

[Santoro]

I confirmed visually that the switch wasn't shorted. I googled a bit without luck, what's an 'apron' in the context of a leaf switch?

[Santoro]

The resistor network seems OK after all, I was testing it wrong.

I also removed the harness that connects the pop bumper switch to the CPU board.  The coil return is still stuck to ground, which indicates to me that it's not the switch or a short in the wiring telling the CPU to activate the coil. 

So to recap:
It's not the transistors or coil (replaced all these TWICE, and they still test out OK)
It's not the PIO
It's not the switch
It's not a shorted wire to the switch or the coil.

wtf

[Santoro]

I took this to RGP.  http://groups.google.com/group/rec.games.pinball/browse_thread/thread/ae6e3cf6e00a3493#

[shardian]

The apron is the plastic skirt thing that the ball rolls onto to activate the pop bumper. At the base it comes to a point, and that point rocks in a cup attached to the switch. Whenever it rocks it depresses the switch. If the point or the cup gets worn or dirty, it can get stuck in the rocked position and lock on your coil.

[Santoro]

Success!  I had lost the tinning through the pin 5 hole of U50. Threaded it and all is f i n a l l y well with the pop bumper.

[wxforecaster]

Congrats. Hopefully this helps me out. I've been stumped by my Whirlwind which locks on the right slingshot as soon as you power the game on. At least you've given me some ideas to check!

Evan