Hi all, you might have seen my post in the other forum, I am having some issues toasting the main fuse on my Williams World Cup 78' System3 pin whenever the switch is turned on. I am pretty convinced that it is a short on the transformer in the head of the machine. I am getting resistances of approximately 1ohm between pins 1&2, 3&4, 5&6, 7&8, which are each windings. It seems kind of strange however that all the windings would be shorted.

I was hoping someone with an old Williams system 3 could measure the resistance of the windings in theirs? I've attached the pic of the schematic (poor) and transformer.

Thanks for the help.

This is normal, e.g. the DC resistance of a winding is dependant on the wire gauge and the length.
For AC transformers and AC motors, it is the inductance that limits the AC current flow
(incl core & number of turns).

Did you disconnect ALL secondaries of your transformer incl all bridges and GI ?

What fuse type and value are you using for the main fuses which keeps blowing?

Is the AC line filter ahead of the main fuse, or after?
(I have seen a few cases of short surge protector across the line filter, in Bally/Stern,
causing to blow the main fuse).

Make sure there are no short under the transformer lugs, to the ground plane.

Cheers,
- Sylvain.

If you disconnect everything from the power supply except for J1 and J2, do you still blow the fuse? Disconnecting everything but J1 and J2 isolates the power supply from the rest of the game. If you're still blowing the fuse with nothing else connected, the problem is likely on the power supply. If the fuse doesn't blow, the problem is elsewhere in the game and you can take the opportunity to check for proper voltages at the test points on the power supply.

It's highly unlikely that your transformer is the problem.

Thank you for your replies.

I have neither J1 nor J2 hooked up to the power supply board. I disconnected both bridges (lamps/solenoids) and removed the fuse on the fuse card (GI I believe you are talking about). As per the schematic these are the connections on the secondary of the transformer, also I have disconnected basically every other plug. I even un-soldered the other wire on the fuse card just to make sure it wasn't shorting out against anything further down the line.

On the secondary is it normal to have extremely low resistances as well? I am getting in some cases much less that 1ohm. My next move will be to pull the transformer out and take a look at the secondary/underneath to determine if I have any shorting.

I am using a 7A fast blow, with nothing connected I really didn't expect to see much current draw at all. I'm not sure if its the fuses themselves but they aren't just breaking, there is always a dark burnt portion and the wire is in a number of pieces, not usually what I see on dead fuses.

The line filter is after the main fuse. The power comes in through this black box mounted on the rear under the playfield (not sure exactly what it is?), then through the main fuse and next to the AC line filter. See attached pics. I have removed one leg of the varistor as well which was suggested by another mate as a possible failure, and no luck.

In addition, with the plug from the output of the line filter (input to the primary of the transformer) unconnected, there is no blowing of the fuse. It is only once the transformer is connected the fuse blows. Lets hope for something shorting to the ground plane underneath...

Thanks again.

That big transformer in the back of the machine is junk and can be toss in the river.

Is it doing anything? I measure just over 120V at the wall and I measure just over 120VAC at the fuse/line filter...

Quoted from Buchy

Is it doing anything? I measure just over 120V at the wall and I measure just over 120VAC at the fuse/line filter...

It's an isolation transformer installed by the op. In the '80's, the Ontario Government legislated the installation of those transformers into coin-op amusement devices to isolate the machines from one another. This prevents shocks if the ground prong of the original power cord is missing and you're standing barefoot in water while playing the machine and simultaneously touching metal on the machine beside it.

They're usually installed before the power switch and draw current from your power outlet constantly. They're useless (IMHO), a power drain and serve to make the machine weigh about 20 pounds more than it needs to. They make great medieval combat devices, but they're pretty much junk beyond that.

Unplug the original power cord from the isolation transformer and check the 3-prong plug and replace if necessary with a new one. Remove that isolation transformer and see if you can come up with new ways to break things with it.

Of course, this has little to do with your fuse problem...

By the way, if you haven't already, you'll probably want to read up here. It's the bible and will answer 90% of your questions: http://www.pinrepair.com

Hmm interesting little pinball history there thanks! Something to take care of after... but like you said... little to do with the fuse. I noticed it would hum as soon as I plugged in the power cord, even with the switch off. And yes, I've read through the Williams Sys3-Sys7 repair from front to back a couple times.

I'll pop off the transformer when I get home tonight and give an update.

Again thanks all for the help.

Ok I have taken off the transformer to check its belly and backside, nothing out of the ordinary. It's interesting that the transformer installed by the previous op (big black one) has ~1.5 ohms resistance on the primary and secondary.

As I mentioned, with the transformer in the head, the primary windings all seem to have a resistance of 1ohms, however on the secondary I am seeing some with resistances far less than this <0.5ohm. Is this normal?

To me, with everything disconnected, line filter & varistor checked, I will bypass the black transformer, if I still have a blowing fuse all I can point the finger at is the transformer... I know it's "highly unlikely" but it seems like the only likely solution for me.

Thoughts? Thanks.

edit: Not sure if it is because I powered it a couple more times or because I wiped down the contacts well, but I can see, in some cases, less than a half ohm on the primary windings. Across the two windings 1&4 I don't even get an ohm resistance. Must be a toasted transformer... tough luck I guess. Anyone know where I can source one?! heh