Troubleshooting a Star Wars power supply

mgmchenry

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Hello, all. This is my first post.


I think I have a bad transformer, but I'm not sure.


I'm new to this, so I was hoping this was a good place to find some help. I haven't done much with electronics since high school, so I'm not too sure of myself.


I lucked into getting a non-working stand-up Atari Star Wars cabinet a few years ago and am just getting around to trying to repair it.


When I plug it in and turn it on, I get working marquis light, coin slot lights, and a spinning fan, and the noise of the high-voltage powering up on the display.

However, I don't see or hear anything.


The power cable had it's ground plug cut off, so I put a new end on it first. No change.


I unplugged everything from the power supply except the incoming AC and the power switch to check the voltages. The AC voltages coming out of the power supply are correct, according to the schematic I downloaded from the incredibly useful gamearchive.com.

There is supposed to be a 10V DC output, but I'm reading about 6V.

If I disconnect the rectifier and check the AC output from the transformer, I get 10V AC. If I check the power coming out of the rectifier, it's more like 9V DC. I would swear that the first time I measured the voltage coming out of the rectifier, it was 10V, but every time I've measured it since, it's 9V. Maybe this is from the transformer heating up, or maybe it's from me making bad observations.

I don't have an oscilloscope to get any better information on the wave form.

When the capacitor is added to the circuit, it takes a *long* time to charge up. Voltage drops down to 3V and slowly climbs up to about 6.

I replaced the rectifier and got the same results. The "Big Blue" capacitor is something like 27,000 microfarads if I'm not mistaken. With essentially no load on the circuit, I figured I could try to substitute another one I had on hand - a 4,600 microfarad cap and see what happens. Exact same behavior - slow charge up to 6V.


So working on the theory that the transformer isn't able to deliver the amount of current needed, I hooked up an LED from a PC hard drive indicator as a load. With either capacitor in place, the LED ligts up for about a second and dims out. Without the capacitor, no light.

I would figure I could power the little LED from the 10V AC coming off the transformer, but again no.


Sorry for the long post. It looks to me like the rectifier, the fuses, and the capicitor are working and I'm not getting what I expect from the transformer. It's not supplying enough current.

Can a transformer fail in this way? Am I on the right track?

If I am, I haven't figured out where to get a replacement transformer. I'm thinking I might have to build a custom power supply with parts that I can get a hold of.

Thanks for any ideas.
 
Last edited:
Oops

Correction. Farad. Spelled with an "F", not a Ph. After Michael Faraday. I really knew that.
 
No, wait

It's not the transformer.

I posted that after a day of very frustrating troubleshooting. The fuse coming out of the transformer on the DC circuit had a bad connection.

Now I just have to figure out what 16 beeps means.
 
This explains the beep test and the results.

RAMROMBeepTestInstructions.jpg


RAMROMBeepTestTable.jpg
 
Have you tried removing, cleaning the legs, and reseating each ROM?
 
The ROMS actually seem to be OK. The interconnect between the main PCB and the AVG seems to be temperamental. If I get the ROM/RAM errors, I re-seat it and it goes away.

I have a machine that gives 16 good beeps for all the ROMS but other than that does nothing. I started working my way through the troubleshooting guide today but after 30 minutes of trying to figure out how to find the reset line at location 2C, I had to move on to something else.

I was about to complain about the chips not being labeled when, just now, it became obvious to me how they are labeled on the silver trace rows running across the board. Duh!

Reset line found and checked. If the obvious stuff takes me this long... wish me luck.
 
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