Pinball Machine - Transformer

So I've finally found some time to get a chance to work on a vintage pinball machine I've had in collection for awhile since the driver board has reached my front door. Whenever the switch is flipped the main fuse is blown (the first fuse from the wall). Nothing is really connected except for the power supply board so I figure it must be a hard short somewhere.

The main transformer in the head is labelled 1-8 on the input side. The schematic shows coils between 1-2, 3-4, 5-6, 7-8. Measuring the resistance across all of these gives me an 'open circuit' reading for 1-2, 5-6, 7-8, and only ~1ohm across 3-4. Do I have a short in my transformer causing this, or is this normal in some cases? Could be a nasty fix. Thanks.

You state it's labeled 1-8 on the input side and there are separate windings! This would be unusual as the input side would only have multitaps to handle different voltages. Where does the power connect to the input side? What machine is it?

Mike.

First of all my apologies for posting in the wrong section, and thanks for the help.

Sorry for the poor pictures but hopefully you can make it out. The two wires from the wall one goes to pins 4&8 and the other to 1&5 as per the schematic. I see almost a short between pins 3&4 whereas 1&2/5&6/7&8 are almost open.

The machine is a Williams 1978 World Cup.

Cheers.

**broken link removed**

**broken link removed**

It sounds like there are problems with the transformer but it doesn't look to have suffered much. Can you disconnect the secondary to confirm it is the transformer? From the picture, **broken link removed**
it looks like you can just pull the plugs from the board above the transformer.

BTW, I have a Williams Monster Bash that I fix regularly and my friend has an older machine (Bally, Lost World) that I also get to "maintain".

Mike.

Thanks Mike, really appreciate the help. Good to hear there are other pinball fanatics around!

I guess I should disconnect everything from the secondary of the transformer? There are 2 plugs that go into the power supply board, 8 connectors that go to 2 bridge rectifiers and then another one that goes through a fuse (which can be easily removed) for the display power.

I'll do so and get back to you about the fuse.

Thanks.

Update:

I have disconnected all of the wires from the secondary of the transformer, the 2 plugs, 2 bridge recitifiers and display fuse. Again I immediately have the main supply fuse blown leading me back to the transformer.

What is my next step here? Is there a way to fix it or must I now source a replacement?

Thanks.


edit: It seems my first measurement of the transformer was off due to corroded leads. I am not measuring under 1ohm between each 1&2, 3&4, 5&6, 7&8. Is this normal or are all the windings shorted?

Also Mike, what is the black box under the playfield that the power wire goes to first, even before it reaches the fuse? When I measure across the white and black wires of the power wire I see ~1.5 ohms which also didn't seem right to me...

Dalaran said:

edit: It seems my first measurement of the transformer was off due to corroded leads. I am not (should this say now?) measuring under 1ohm between each 1&2, 3&4, 5&6, 7&8. Is this normal or are all the windings shorted?

Click to expand...

If you are now measuring less than 1Ω between windings I suspect the primary is shorted. The only way to be sure is to remove it completely and measure it.

Also Mike, what is the black box under the playfield that the power wire goes to first, even before it reaches the fuse? When I measure across the white and black wires of the power wire I see ~1.5 ohms which also didn't seem right to me...

Click to expand...

Not sure what you mean. The only thing normally before the transformer is the power switch which is normally placed near the front right corner under the cabinet. These switches can also go short circuit so would be worth checking out.

Mike.

Thanks again for your help/time.

The power cord from the wall socket comes in through the back of the machine and into this black box below:
**broken link removed**

From here the hot wire goes through a fuse and to grey box shown below, as the neutral wire goes straight to the box. This is the fuse that is constantly blowing. The switch is then after this (on the brown wire on the output of this grey box) on the way to the suspect transformer I showed earlier.
**broken link removed**

What sort of resistance should I expect to see across a winding of the transformer?

Thanks.

I have a 220-110 250VA transformer that I just checked and the secondary (110 winding) measures 2.7Ω. Your transformer looks about the same size and so the readings you are getting may be correct. Sorry if I mislead you but I am surprised the DC resistance is so low.

As for the other boxes I'm afraid I have no idea either. Maybe some kind of suppressor or lightening protection. Try unsoldering the primary of the transformer and see if the fuse still blows.

You can also ask on the **broken link removed**, there are some pretty knowledgeable people over there.

Mike.

Good idea with taking the primary off. I'll try this later this afternoon/evening.

Again Mike, your help is always appreciated.

edit: the primary wires come through a connector just before the reach the transformer. With this unplugged (primary disconnected) the fuse does not blow. *scratches head*

I guess the next step is to cut/dismantle all the wires on the secondary making sure they are not connected anywhere and then test. If it still blows then it has to be the transformer...

Thanks again.