Stargate power supply unreg 12 volt question

RobMcRaf

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I am in the process of going back to the orignal power supply in my Stargate. Saltbreez seems to think that the switcher is killing the eeprom. Everything checks out but I am concernd about the unreg 12vdc. it is at 13.59 with no CPU board connected. Is that OK? Thanks!
 
I am in the process of going back to the orignal power supply in my Stargate. Saltbreez seems to think that the switcher is killing the eeprom. Everything checks out but I am concernd about the unreg 12vdc. it is at 13.59 with no CPU board connected. Is that OK? Thanks!

What EEPROM?? I'm not aware of one being on Williams boards.

If you're talking about the RAM (4116)... the datasheets for it I find show specs for Vdd of +/-10%, i.e. 10.8-13.2V on the 12V line. So yes, applying 13.6VDC to those RAMs is a bit of an issue. However, if you do the 4164 RAM mod, it becomes a moot point (those RAMs don't use 12V).
 
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Hmmm, I thought the OP was saying that his switcher outputs an unregulated 12V, and that it was being used as both the unregulated AND the "regulated" 12V sources on the boards.

If that's not the case, then what I said doesn't really make sense. Perhaps the OP should clarify.
 
What EEPROM?? I'm not aware of one being on Williams boards.

If you're talking about the RAM (4116)... the datasheets for it I find show specs for Vdd of +/-10%, i.e. 10.8-13.2V on the 12V line. So yes, applying 13.6VDC to those RAMs is a bit of an issue. However, if you do the 4164 RAM mod, it becomes a moot point (those RAMs don't use 12V).

Sorry, misspoke myself. Was referring to the CMOS.

Have done th 4164 with different boards and each one has it's own set of wonderful issues.
 
Was referring to the CMOS.

If we're talking about CMOS RAM at location 1C, it isn't powered by 12V, regulated or unregulated.

It gets regular +5VDC (less the voltage drop across D9) when the power is on, and battery voltage (less the voltage drop across D10) when the power is off.
 
The unregulated voltages will be about 10% - 15% higher than the spec. This is due to the wall voltage being higher now than it was back in the 80's. Back in the 80's wall voltage was nominally 110VAC. Today's wall voltage is nominally 117-122VAC. SO that will push the unregulated voltages higher.

This is generally not an issue.

The +12V unregulated on the MPU board is only there to act as a trigger for the CMOS protection circuit. when that voltage drops below a threshold value the CMOS is put into write protect mode.

The issue with switchers is due to a hardware bug in the 6809. WHen the supply voltage drops on the CPU chip, it randomly writes to memory. If that memory is RAM, no biggy, it will be refreshed when the game is powered up next time. If that memory is ROM, again no biggie, you can;t write to ROM. If that memory is the CMOS, you are in trouble. Unless the write protect circuit has kicked in. With switchers, the voltage drops on the +5 volt as fast or faster than the +12 volt (there is more load on the +5V). In that case, the memory protect doesn't have any warning, so it can't kick in.

The Williams power supply was designed with a very large capacitor that can power the +5V for a few milliseconds while the +12 unregulated drops off. This gives the memory protect on the CMOS time to activate and protect your settings and high scores.

That is why it is recommended to rebuild the Williams power supply rather than put a switcher into classic Williams games. Moon Patrol, Motorace USA and MakeTrax use a different design and don't suffer from 6809 hosing.

ken
 
Power sequence

The unregulated voltages will be about 10% - 15% higher than the spec. This is due to the wall voltage being higher now than it was back in the 80's. Back in the 80's wall voltage was nominally 110VAC. Today's wall voltage is nominally 117-122VAC. SO that will push the unregulated voltages higher.

This is generally not an issue.

The +12V unregulated on the MPU board is only there to act as a trigger for the CMOS protection circuit. when that voltage drops below a threshold value the CMOS is put into write protect mode.

The issue with switchers is due to a hardware bug in the 6809. WHen the supply voltage drops on the CPU chip, it randomly writes to memory. If that memory is RAM, no biggy, it will be refreshed when the game is powered up next time. If that memory is ROM, again no biggie, you can;t write to ROM. If that memory is the CMOS, you are in trouble. Unless the write protect circuit has kicked in. With switchers, the voltage drops on the +5 volt as fast or faster than the +12 volt (there is more load on the +5V). In that case, the memory protect doesn't have any warning, so it can't kick in.

The Williams power supply was designed with a very large capacitor that can power the +5V for a few milliseconds while the +12 unregulated drops off. This gives the memory protect on the CMOS time to activate and protect your settings and high scores.

That is why it is recommended to rebuild the Williams power supply rather than put a switcher into classic Williams games. Moon Patrol, Motorace USA and MakeTrax use a different design and don't suffer from 6809 hosing.

ken

Great explanation. That is what Saltbreez was trying to get across to me, I think :). Most everything was patched into the harness from the switcher, and now I will undo it and get things restored to original. Thanks everyone!
 
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