The ASIC has a real time clock and a small amount of SRAM in it to store the time and date. The ASIC's SRAM data gets corrupted when the battery voltage drops below 2.4v. The clock also slows down when it gets close to the voltage threshold the clock time of date corrupts.

If you plug a 3-5vdc wall wart, like a phone charger, into the service outlet and then plug that into the battery connector on the MPU, the clock will continue to run when the game is turned off. If you want it to keep retaining memory for a day or two if the line cord gets disconnected, add a 1F 5.5vdc super cap.

No real harm in having the the time and date wrong unless you want the midnight madness and features like in circus voltaire where the it has the time and date high score list of people that made it to the wizard mode.

You can replace batteries with the game powered on, doing so will prevent any settings (including hi scores) from being lost.

I do this and prefer using lithium batteries, I just cant stand my RTC not working...and yes I realize its just a clock and you can make it not display...but it's still there and I will know its not working with the game turned off, even if no one else does.

This says it all:

WPC89 Clocks (resized).jpg

A wall wart seems impractical, almost comical in a way. Do you really want to be trusting cheapo eBay, etc wall warts, even if they're outputting regulated voltages.. to be on 24/7 and while you're away from your home. Just takes the thing to fail or go out of spec to kill your ASIC & cost you far more than your high scores.

Lithium batteries remotely mounted still seem the best choice if you need to maintain the RTC. I get it for TZ, but for many other games that don't really utilize the RTC in-game I'd not personally worry about it. Not gaining much upgrading to NVRAM and still keeping batteries connected, other than being able to change batteries out when the machine is off. IMO not worth the risk desoldering the low-power SRAM if you're using batteries.

Just had to chime in since this thread is still alive and kicking

ahhh... never thought of that. I always had the game off when replacing them. Which now would be the only benefit if I decided to still use batteries. I also installed the modded ram chip mainly just to do it, out of curiosity. I had one of the stupid traces lift off, really wish they had a protective coating on these boards back then. Other then that it came out really well.

Do you trust the wall wart that charges your $600 cell phone? 120/240vac to 5vdc have been made by the BILLION, i dont hear about many failing.

What does fail is batteries and they puke garbage.

My cell phone is like $50 and not really.

I'd definitely not trust a cell phone charger 24/7 connected to the ASIC with possibility of power surges, lightning strikes, etc. But do what you want. And if others think it's a great idea, awesome. Just my opinion that it seems ridiculously overkill and not without its own problems.

I have never had a wall wart fail, and use dozens of them at a time 24x7 for the last 30 years... guess I have been lucky.

Maybe this is an opportunity for a new feature on an NVRAM adapter... add a zener and a fast blow fuse as protection on a feed for the 5v standby.. add a two pin connector for people to add an optional feed that would then be protected on its way to the ASIC?

Every new problem is an opportunity for innovation!

Mac

Just as a word of caution, the $5 chargers one can buy from eBay can have radically different actual specs, outputting wrong voltage, wrong amperage. So either test the wall wart or use an official Apple one. Probably Samsung too, I just don't know enough about their QA

Yeah. I am already playing with a crowbar circuit for something like this.

The wall warts are reliable as long as you don't get crappy ones from China. Big Clive on YouTube has taken apart counterfeit China ones and they usually lack certain protection circuits or just in general cheaped on the design with less components. Everyone just leaves them plugged into the wall for years on end.

Shop for wall warts with the UL label. This normally indicates extensive lab testing and assembly with quality parts. Not necessarily so, with CE or CES.