Re: TZ Ground Short Issue

in article
f6ab79ac-1524-49ca-80d7-63c927832e07@xxxxxxxxxxxxxxxxxxxxxxxxxxxx, Metahugh
at metahugh@xxxxxxxxx wrote on 3/9/09 7:42 PM:

What was your "original problem"?  :-)  Was it?

My main issue is something is shorting voltage to my switch matrix
chips on my CPU.  U20 keeps getting blown.

Please don't put another U20 in there again.  Poor things.

LOL.

Did you check the voltage on J206/207 pin 3 (the plug with the wires coming
from the playfield) with your driver board connected?  If it is that stray
70 VDC, you will fry another U20.  Compare it to the other wires on that
plug.  Also check out pin 3 of J212.  If they are all the same, then go
ahead and try another U20.

If it is hot, then back to tracing down that stray voltage again.  Please
see my earlier posts for a systematic way to narrow down where it is coming
from.

Here is what I have found. I have only the coin door switches
connected (J205). J212. J206 and J208 are disconnected. I did the
diode test. I put one end of test wire on pin 3 on J206 for column
3. I connect the other end which is attached to a diode to each pin
on J208. Pins 1-5 are all coil switches and when each pin is touch
the associated coil for each fires. Is that normal?

Yes.
Just to check, you did this in the switch diagnostic test mode?
The banded end of the diode is towards J206?
You must have replaced U20?
Then yes, it should do this.


As a test I tested switch 28 on column 2 to see if the rocket kicker
would fire when I registered the switch and it doesn't.

J206-2 to J208-9? No the solenoid does not fire, but you should hear a beep
from the pin audio indicating that the switch has closed.


As far as voltage goes pin 3 of J212 is is 11.6volts. I am seeing the
same voltage on every pin of J206 and J208 as well. This is all with
the driver board connected.

With your DVM set to 30 or so VDC and using the ground braid, this is good.
All are normal.


I am no longer seeing 70volts on the ramp. That was all because I
didn't have the driver board completely secured... at least that
problem was solved when I completely screwed down the driver board.

I don't see how, but I will go with that.


Here is a stupid question. With J208 and J208 disconnected should I be
reading voltage on the connectors coming from the playfield? Where
does the voltage come from? I'm seeing about 4.3 volts but not on
every single pin.

Hugh


I am not clear from your question, if you are reading these voltages on the
pins of the CPU board, or the female connector plugs with the wires going to
them?

Just FYI, I tested connector J207/206 (the plug, with the wires coming to
them - not the circuit board) and I read:

pins 9 & 7 =12.9 VDC
Pins 2 & 1 =11.5 VDC
All others ~ 0 VDC

All voltages were taken with the J206 plug disconnected from the CPU board.
Columns are high because they have normally closed switches on those columns
(with pinball's loaded). The other columns do not have normally closed
switches so their voltage is low. This is with J208 connected. With J208
disconnected, the voltages on J206 plug read:

Pins 9 & 7 =12.9 VDC
All others ~ 0 VDC

In your next note, you say:

J206 pins 7 and 9 are reading 4.2 volts. This is on the connector
itself not on the header on the CPU board. Every pin on the CPU board
is reading 11.6 volts

J208 shows no voltage on the connector itself. Again not measuring at
the header on the CPU board.

Hugh

I don't like that J206 is reading 4.2 V DC on the plug itself pins 9 & 7,
when mine is reading 12.9 VDC.

Just to check, this is taken with plugs J206 and J208 disconnected from the
CPU board? And this is the voltage on the plug itself with ground connected
to the pin braid?

If so, I am not certain what this means. Please try checking all those pins
on J206 again for AC. This is important.

Wires 9 & 7 are columns 8 & 7. They are connected to the clock. Hours to
column 7. Minutes to column 9.

Do you have the original Williams clock boards, or a retrofit? If they are
aftermarket, I am not familiar with their voltages.

If you do not measure any AC on any of the wires in plug J206, then I see
nothing from the playfield that is causing your U20 to fry.



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