need help w/power supply on Stargate

toecheese

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I have a Stargate machine that has power issues. First I got intermittent errors on startup, then it went dead completely. I opened it up and when powered on, only 2 of the 3 LEDs on the PS were on. I turned it off, checked the connections, and when I turned it on again now none of the LED's come on. Additionally I don't hear the familiar hum and "thunk" of the relay. I tested the fuses (all good) and visually inspected the board, and I do see that one of the pins on the plug leading to the large black heat sink looks burned (see photo).

I gather I need a new power supply, but how do I know if it's the PS board or the big transformer that's bad? Is it normal not to hear the hum and relay "thunk" if it's just the board? I thought it was the transformer that made those sounds. Not sure which wires to test on the transformer to see if it's outputting power.

Lastly, if I have a bad PS, I'd prefer to buy a new switching model rather than rebuild this one (I care more about reliability than I do original innards). Where can I get one of these?

Any advice is appreciated.
 

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Doesn't matter where the switcher comes from, they are not a good idea in Williams games, if you care about your settings and high scores.

If you are worried about reliability, these games have lasted almost 30 years, many of them spending years running 24/7 under horrendous electrical conditions. It is unlikely that you will ever see a switcher last a significant fraction of that.

The 6809 chip that powers the Williams classic games has a flaw in it that causes the CPU to write randomly through the address space when the power dips below 3 volts or so. To work around this the Williams linear power supplies contain an oversized filter capacitor (that big cap on the power supply board - 18,000uF). This acts as a reservoir of power to continue to supply the CPU board with +5V for several milliseconds. On the CPU board is a circuit that senses when the +12V unregulated power is shut down (it drops in voltage nearly instantly after the AC power is shut down). When this circuit senses the 12V is shut down, it engages the CMOS write protect circuit, turning the CMOS into read only mode so that the CPU can't trash the high score data, bokkeeping data or settings.

Switchers do not have the extra reservoir of +5V power and both voltages go down simultaneously. This does not provide the CMOS write protect circuit enough time to react and the CMOS is vulnerable to the CPU overwriting the data on it.

Which is why you hear the whines and complaints of people who just lost their all time high score or who have to reset the game to free play all the time.

ken
 
+1 YellowDog and andykmv.

Rebuild it yourself or send it to Dokert or YellowDog for a rebuild. The only way to go.
 
It is $20 + parts + return shipping. Normally, unless the PS board is in really bad shape it runs about $12 for parts. The two big items are the big bridge rectifier (about 50% of the time), they are $4 and the big capacitor (about 50% of the time), they are $6 to replace. Most of the time it is usually the smaller capacitors, the voltage reglators and any burned headers.

Surprisingly, a great deal of the time I have to replace several fuses as the operators just tended to shove whatever they have handy into the clips with a mental note to "fix it later". The worst I have seen was a set of ceramic 100A fuses placed where the 7A slow blow fuses normally go. Needless to say the bridge rectifier, the diodes and a half dozen resistors had to be replaced as they were all burned up. :eek:

PM me for more details on shipping, address, etc.
ken
 
I have a Stargate machine that has power issues. First I got intermittent errors on startup, then it went dead completely. I opened it up and when powered on, only 2 of the 3 LEDs on the PS were on. I turned it off, checked the connections, and when I turned it on again now none of the LED's come on. Additionally I don't hear the familiar hum and "thunk" of the relay. I tested the fuses (all good) and visually inspected the board, and I do see that one of the pins on the plug leading to the large black heat sink looks burned (see photo).

I gather I need a new power supply, but how do I know if it's the PS board or the big transformer that's bad? Is it normal not to hear the hum and relay "thunk" if it's just the board? I thought it was the transformer that made those sounds. Not sure which wires to test on the transformer to see if it's outputting power.

Lastly, if I have a bad PS, I'd prefer to buy a new switching model rather than rebuild this one (I care more about reliability than I do original innards). Where can I get one of these?

Any advice is appreciated.

Get the PS rebuilt.
And while waiting - replace that burned connector. Don't go the IDC route as on the original -- IDC's were used to save $$ by cutting assembly time. Instead, go with a crimp type connector. If you're worried about it burning again, go with the high current plugs such as these:
http://www.greatplainselectronics.com/category-86.asp

Ed
 
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