What is eating the battery

[therockinelvis]

I gave a machine to my cousin and it gets a code 12 every 2 months. He lives an hour and a half away and it's getting old going to change the battery. I've got machines that the battery lasts more than a year. What gives? I thought it only held credits in memory.

[shortrackskater]

Did you buy the batteries on Ebay? I bought some from one vendor (for fixing watches) and they all died within a few months! Now I make sure the listing shows the "good until" date on the battery.

[CommTech]

Did you buy the batteries on Ebay? I bought some from one vendor (for fixing watches) and they all died within a few months! Now I make sure the listing shows the "good until" date on the battery.

There are really no good suspects in the battery circuit that would cause the battery to drain prematurely.   Be sure to measure the battery voltage before you install it;  Should be at least 3.6 volts or higher.  Then check it again in circuit...  Again the voltage across the Battery should maintain the 3.6 volts if it is good. 

[therockinelvis]

Pretty sure I bought them from MCM. 6 machines all have same batteries, just this one eats them. And he plays the machine several times a week.

[cowboygames]

I was thinking there's a circuit that opens and closes depending on whether the machine is on or off. If that circuit was bad your battery would go bad pretty fast. I could be wrong, it's happened before

[knagl]

While not a perfect solution, you could consider installing a battery holder on the board so then replacing the battery in the future would just be as simple as popping in a new battery into the holder, rather than having to solder it each time.

[CVslots]

Or Jim, maybe consider switching boards with him? That way, you could narrow it down and pinpoint what the problem may be?

[CommTech]

I was thinking there's a circuit that opens and closes depending on whether the machine is on or off. If that circuit was bad your battery would go bad pretty fast. I could be wrong, it's happened before

There are diode junctions that prevent the power supply from feeding back to the battery and also to prevent the battery from back-feeding into the power supply. But even if one of those were shorted, I don't see a path to discharge the battery. 

There is a yellow 10 uFD / 35 Volt Tantalum capacitor, located directly in front of the CMOS chip, that if it were leaky, may slowly drain the battery.  I have seen very low value Tantalum capacitors short due to poor circuit design by having the capacitor rating too close to that of the supply voltage.  In this case, that does not apply.     

CVslots has a good idea, if you can swap boards ...

Try removing one side of the battery, then momentairaly short that 10 uFD capacitor to discharge any residual charge, then take an ohmmeter and measure across it ... The resistance should quickly rise to a very high resistance if it is good.  If the resistance remains low, then first pull the CMOS chip to be sure that is not causing the problem, then if the resistance stays low remove the capacitor and check again. 

[Jon b]

If those diodes start to leak reverse voltage or short, the power supply could be charging battery. that would cook it. Or the battery could discharge through other components. 

[therockinelvis]

After getting this board back home. I found it to be -.2vdc. The battery is in right but it has reversed. If I switch my leads to red to - and black to + it reads on the plus side. Very strange. This board had a Piggyback??? cmos chip meaning it chip was mounted on another mount then inserted in board. Don't know if it had anything to do with it. I have changed it and will put in a game to see what happens.

[Badbaud]

If it is a S+ there is a Tantlum capacitor just above the RAM chip that goes bad and sucks life out of the battery

I have encountered at least 5 boards with this same bad capacitor, replace the cap and the battery remains stable for months if not years.

You can't just cut the cap out of the circuit due to a little known engineering principal called "Rate of Rise" which basically states that semiconductors (your RAM chip in this case) don't like being banged with DC voltage immediately, it causes them to blow their inards. That is why capacitors are put across 5V and ground in electronics.

Also found a couple of Bally 5500 boards where the bypass cap for the RAM chips was causing the same problem and it was only a .1 uF.