Re: TZ Ground Short Issue

On Mar 5, 9:34 pm, martin <martin.reyno...@xxxxxxxxx> wrote:
On Mar 5, 6:17 pm, The Hammer <LHNewsgr...@xxxxxxxxxxx> wrote:



in article
c59aae94-fca7-406b-85b0-5c2cd84f8...@xxxxxxxxxxxxxxxxxxxxxxxxxxxx, martin at
martin.reyno...@xxxxxxxxx wrote on 3/5/09 3:35 PM:

Minute amounts of voltage don't necessarily mean a whole lot.  You
could be getting that from any number of places and unless you
completely unplug the entire playfield from everything in the backbox,
I wouldn't worry about that so much as the 70V that's obviously going
somewhere it shouldn't.

Tonywww.greatlakesmodular.com-Re-EngineeredPinballParts!- Hide quoted text
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- Show quoted text -

Also a high impedance meter, which is what basically all meters are,
may measure "ghost voltage". What this is that you measure voltage
that really isn't there due to no load. Some new meters have a low Z
setting for measuring presence of anwanted volts. The new Fluke 289
meter has a 3K ohm low impedance setting for checking power. You could
basically duplicate this feature by running a 3k ohm resistor from
ground to your ramp that has the volts you are measuring. Hook up all
your plugs and recheck volts from ground to the ramp. If volts are now
zero, you've been fooled by the ghosts. If volts are still 74 you've
got a major short to the ramp. It's not on the power board, or AC
power supply, lack of third prong, or anything else. It's a short
right on the ramp.- Hide quoted text -

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You have a coil lug shorted to the ramp, or a trapped wire. That is
the only reasonably explanation. The only question, is it high side or
low side?

For a crude test, ground the ramp. If a solenoid fires, you have your
culprit. If a fuse blows, then it is a power lug short and will be
tougher to find.

in article
72e1329d-279a-41bf-8a4f-450023e23...@xxxxxxxxxxxxxxxxxxxxxxxxxxxx, Metahugh
at metah...@xxxxxxxxx wrote on 3/4/09 8:14 PM:

I turned the game off immediately and started
looking for a short somewhere around that ramp.  I put the playfield
down and touched it again, and it is still electrified!

I too thought that it was the solenoid voltage that was shorted.  But Hugh
says that he turned off the game and it was still electrified.

removed the driver board completely.  It still shows some voltage.  My
meter was set to 200mv and I was seeing 24.5 with the driver board
removed.  There is something shorting voltage and I am guess once I

I blew it.  I saw 24.5 and thought volts.  If his meter is set to 200mv,
then he is reading 24.5 mv which is nothing and it is a ghost.

Back to the driver board.  He could go hunting for what is shorting.  I like
the fuse short idea.  Or he could start by doing what I had in the original
post:

Power off. Plug in J102 and unplug the three plugs - J109, J107 and J104.
Plug in those three one at a time (turn off power between each one) until
you have the problem again.

This is quick and will tell him what color to look for as a short.  If it is
J107, he could then remove F104 and 105 one at a time (with power off) and
that would tell him if it from pin 2 (Violet-Yellow) or pin 3
(violet-orange).  Once he knows, look for that wire. [J107 pin 1 F103 is not
used in TZ.]

Unfortunately, it could be one of the return lines from a solenoid.  That
would give the same measured voltage, but the current would be through the
coil.  If he knows if it is from pin 2 or pin 3, that would narrow it down
to 8 solenoids.  

He could short that ramp.  The solenoid should fire and he has it.

If it is J109, that narrows it down to the magnets, miniplayfield magnets,
gumball motor, or left ramp diverter.  J104 is fliptronics.

Or as suggested, he could hunt and maybe find it pretty quickly.

_______________________________________________________________
VisitOregonSouthCoast.com

http://www.visitoregonsouthcoast.com/-Hide quoted text -

- Show quoted text -

DMMs can always be a bit fussy, especially around pinball grounds. For
me, the giveaway is that 70VDC.

It may well turn out to be a wire strand, or a solenoid wire caught by
a screw.

SO....

Lift the playfield.
At the very bottom, in the middle, is the coil mentioned above. Make
sure that its lugs and wires are clear of everything.

You can see it in this pic, it has the blue wrapper.

http://www.iobium.com/Twilight%20Zone/DSCN1526.JPG

Alrighty guys. Definitely learned some stuff in this process.

First off, the reason I think I was getting 70v was because the driver
board wasn't completely screwed down. I notice there are mounts on
the board with exposed metal (in the top left and top right corners).
I assume that these points ground the driver board to the game. After
reinstalling my driver board there is no longer any voltage when I
measure at the ramp after securing the board properly. I have a
crappy DMM that I use for basic work and I have a nicer Craftsman DMM
that I use when I need more accuracy. The super low voltage is
definitely a ghost because my Craftsman shows tiny voltage when set at
200mv and my crappy DMM shows absolutely nothing. So for anyone that
may read this in the future, make sure every screw, especially the two
top screws at each corner and the one at the bottom left of the driver
board, are screwed down tightly.

Second my issue with voltage being shorted to the switch matrix.

All I can say is experience counts in pinball. I am fairly certain
that this issue is with the diverter coil. After solving the voltage
issue I grounded the metal ramp to the siderail with a cable with
alligator clips. Nothing happened. Next I tried with my arm. (yeah I
know stupid but I figured since two DMMs are showing zero voltage
nothing would happen). Guess what, the diverter coil slowly fired and
I mean slowly. I tried replicating this by grounding the right ramp
to the siderail again, nothing. It won't fire that way though only
with my arm. So I am going to mount the diverter properly and pull it
apart to see if I have a bad coil or sleeve. So for those of you
that said it was the diverter give yourself a pat on the back.

I will make sure to chime back in and let you guys know if that solves
all of my problems.

Thanks!!

Hugh
.

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