Galaga bad isolation transformer

Arm123

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I rescued a non working Galaga cabinet out of someone's garage... paid $25 for it

Broke into it ;-p and found that it has a few bad fuses. I pulled the game board and tested it in my test rig and it runs perfectly.

Pulled the monitor chassis and it looks great...

I disconnected the main PSU board and started from the AC line filter. Got 120v from the filter but nothing out of the ISO transformers... I then saw that the fuses kept blowing after i changed them.

The only thing connected is the 2 ISO transformers (monitor and Midway psu transformer). I then saw that there is continuity between the AC outputs on both ISO transformers. Disconnected them to make sure...

That cant be right ?.. So im guessing they are bad ? Is that what happens when they (ISO transformers) go bad ?..
 
Those transformers very rarely go bad. The outputs when tested with no power and using an ohm meter will show low resistance and continuity.

What fuses are blowing? Are they the correct type/values?

I'm betting you have a shorted ballast up on the fluorescent marquee light fixture causing a fuse to blow.
 
A ISO transformer is simply 2 pieces of wire wound around an iron core. The wires will be of equal length in a 1:1 transformer. (1:1 ratio being 120v in and 120v out) Since each side is just a piece of wire you'll read low resistance between the terminals.

+1 on Ken's diagnosis of the marquee. Disconnect the hot wire to it and see if you still are blowing fuses.
 
Thanks for your help guys,

I'll take a look in another hour or so to double check which terminals im getting continuity.

Ill also have a look at the light fixture.

I hope its that simple... would be sweet ;-)
 
Checked the ISO transformer and i get continuity between the AC output terminals 0v and 115v with resistance of 2.4 ohms

I also get continuity between the AC input terminals 0v and 115v with resistance of 3.0 ohms

Normal... ?

I also checked the light fixture... Its been converted to a standard light bulb socket ;-p
 
Anyone want to give advise on weather or not this ISO is dead before i try to buy / find an new one ?
 
If there are no wires connected to the output of it, disconnect one of the inputs and see if the fuse stops blowing. If it does then you have one of the rare shorted ones. ;)
 
Checked the ISO transformer and i get continuity between the AC output terminals 0v and 115v with resistance of 2.4 ohms

I also get continuity between the AC input terminals 0v and 115v with resistance of 3.0 ohms

Normal... ?

I also checked the light fixture... Its been converted to a standard light bulb socket ;-p

what watt bulb do they have in the standard light bulb socket ?
If it's 100 watt then that might be blowing your fuse.
 
galaga

Disconnect your plugs at the light,coin door,logic board, monitor.
power up. If fuse blows then odds are your transformer is bad. First make sure your fuses are rated at 120v not 32volts like some fuses are.
Connect one at a time and narrow it down.
 
Did some work on this machine this weekend...

Disconnected all the lights etc from the ISO and tried it with direct AC to it and the ISO is good. So thats nice ;-)

I then rewired everything and replaced a couple fuses. I also found a bad wire going from the AC line filter to the F1 fuse and fixed / soldered that.

Plugged the monitor in and powered it up. Turned the screen control up and saw that i had raster... so im assuming this old G07 is good.

Disconnected the game board and monitor from the wiring harness and turned my attention to the PSU board. Checking all DC output I was able to get +5v with no issues and even got the +7v working fine.

The only problem I have is the +12v on pin 1 of J2. I can't get anything measuring with negative to ground positive to pin1. However, I decided to power the board up anyways.

The game plays fine with sound and all !.. HA !

I even checked the +12v at the 3 pin connector on the Galaga board. No +12v...

Isn't that strange that the game still works with no +12v ? Doesn't the board need this for coining up / sound or something ?
 
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