Williams Transformer Question

Burt6666

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I have a question.The 3 wires from the transformer on my "Phoenix" system 4 game that provide power to the sound board are supposed to have 18.7 VAC on them.I'm measuring 8.8 VAC using the machine ground as a reference and wires unplugged from sound board on all 3.Could the transformer be the issue?
 
I have a question.The 3 wires from the transformer on my "Phoenix" system 4 game that provide power to the sound board are supposed to have 18.7 VAC on them.I'm measuring 8.8 VAC using the machine ground as a reference and wires unplugged from sound board on all 3.Could the transformer be the issue?

This has me wondering... how many times people have thought they had a transformer problem but were measuring their AC wrong. At least 10 :p

When measuring AC you don't use ground as a reference. You put the meter leads across the transformer winding (in this case).

Remember... the transformer is (almost) never the problem. Never (almost).

There are 2 sets of connectors that are the same in that game. One of them happens to let you apply way too much voltage to the sound board and it is definitely possible to mix them up. I did this once on a Disco Fever and fried the rectifier on the sound board.

EDIT: I think I might have a working sound board. I'll have to check. I know I bought one for that Disco Fever and ended up fixing what I had. I sold the Disco Fever a long time ago.
 
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Are these connectors in the backbox?The power ones here are the 2 gray and one gray/white.

I remember that the colors of the housings were different but the connectors were the same. This was near the back box. That's about all I remember. It was like 2+ years ago.

In any case... I would check the voltages on the board. The sound board has it's own power supply. Check for AC into the bridge rectifier, DC out of it, check DC at the ICs on the board, etc...

Once you have known good power you can go from there. Like I said... my machine had a fried rectifier on the sound board. I would start with that.
 
Ok,tested across the wires...hehe.Now have 18.2 volts AC.Must be sound board issue....

This is my shocked face ;)

EDIT: All of the emoticons indicate that I'm kidding around. You're making good progress with that thing. Keep it up.
 
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I had to refresh my memory on that board... fortunately I still have the box of MPUs sitting out from when you were here on the weekend and there's a bunch of sound boards in there.

That sound board is a lot more complicated than what I remember. I didn't look at the schematic but I assume that it generates +12 and +5 from the 18VAC. It's possible that you could have good +12 which would power the sound amp and cause the noise when you adjust the pot (which indicates a dirty pot) and not have the +5VDC present. That could cause the symptoms you have. What I'm saying is I would be sure to verify the voltages before going any further... and pray it's a power problem because that's an easy fix. It should be simple enough to check the +5 at an IC on the board.

But... that's basically a guess.

Once the voltages are verified I would probably check continuity through the connections from the MPU to the sound board. After that you've got a computing system on your hands similar to an MPU. There is a 6802 CPU, 6821 PIA and 2716 EPROM. Lots of stuff could go wrong. I would check the most obvious (easiest) stuff first.
 
That sound board is a lot more complicated than what I remember. I didn't look at the schematic but I assume that it generates +12 and +5 from the 18VAC. It's possible that you could have good +12 which would power the sound amp and cause the noise when you adjust the pot (which indicates a dirty pot) and not have the +5VDC present. That could cause the symptoms you have. What I'm saying is I would be sure to verify the voltages before going any further... and pray it's a power problem because that's an easy fix. It should be simple enough to check the +5 at an IC on the board.


I'd have to pull schematics.....but I believe it also generates a negative voltage....for some reason I'm thinking -12VDC.

The most common problem I find with that era of sound board (if all voltages are good) is leaky caps, bad ROMs, and bad PIA's....but, at this point...anything could be bad :)

Edward
 
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