Berzerk back-up battery ideas

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OK, so I've got the machine running, and of course the old battery has been removed, but I want to keep my "high" scores !

I've seen the solution from Tranquility Base with a loose phone battery and some rather long wires, but I'd prefer to install a lithium cell on the board instead.
The Lithiums will last at least 10 years and this mod has been done often on Williams boards.
However, Williams boards don't charge the batteries. Berzerk does.
In theory, I should be able to "block" the charging supply with a simple diode. Once the machine is off, the battery will supply it's voltage through the diode.
Not sure if that will work OK on a ZPU board.

The other alternative is using a Ni-MH battery like this:
3-V40H-2P_L.jpg


This _can_ be charged and provides the right kind of voltage. However, I was wondering if the IC to store the hi-score data on might be drowning out this one too quickly ?

I suggest these because we use them on fire alarms main PCB's. These keep the programmed data save whenever the mains AND the back-up battery pack are disconnected. So....they're well....uhm....sort of "available" for me ;)
 
You could look at the amp hour rating of that battery and compare it to what would have been original. That should tell you how long the battery will last with the game off, by comparison. I suspect finding information on the original battery would be difficult so that's basically just an informational suggestion... I guess.

Personally I would probably just try what you've got and see what happens. Alternatively you could just use a blocking diode and battery pack as you've suggested. I've done that with pinball machines many times.
 
I just picked up a 3.6v cmos battery. So far so good.

TL-2150%5EP.jpg

Note this is not the exact battery, it just looks like it.
 
You could look at the amp hour rating of that battery and compare it to what would have been original. That should tell you how long the battery will last with the game off, by comparison. I suspect finding information on the original battery would be difficult so that's basically just an informational suggestion... I guess.

Personally I would probably just try what you've got and see what happens. Alternatively you could just use a blocking diode and battery pack as you've suggested. I've done that with pinball machines many times.

In these applications the amp hour rating is not an issue, as the current draw is minimal. The problem with rechargables here is the self-discharge rate. Regardless of the battery's capacity, it will likely drain itself in a month's time if you don't turn the machine on to recharge it.
Your best bet is go with a lithium cell and a blocking diode.
 
...or you could use one of the 2114/6514 NVRAM adapter boards I made 5-6 years ago, and forget about the battery :)

OK how much are they (I need three) and are they available (I need threm now).

:D

Mark, I love your products, I love the SW/ESB kit in my cockpit, but man, you have so much virtua-ware that it's not even funny.
 
Mark, you should start a thread with what you have available and the applications each one is used for. I didn't know this existed, or I would have recommended it.
 
Same here, the past 2 years I've been finding one nice product after another just by running into it on this forum.

But Mark, it's virtua for me until I have the stuff in my hands :D
 
Back on topic.

I just installed a 3V lithium cell and a holder on the ZPU PCB.

To prevent the charge voltage from reaching the battery I added a blocking diode. I installed it by lifting up one of the legs of R29, the one near the + battery connection. Solderderd the diode to between the loose resistor lead and the original soldering island of the resistor, so that it blocks the charging voltage.

Measured everything and everything is OK. The 5.3 Voltage that is trying to charge the battery doesn't reach it, and when powered off the 3 Volts nicely reaches pin 18 (Vss) of RAM 1E.

However when I start up and play a couple of games and register the scores, then turn off the power of the machine and boot back up, my registered scores are gone.

I checked the datasheet of the 6514 RAM and is says Vcc minimum voltage is 2 Volts so the 3 V at the pin should be OK.

I also noticed (but this is on _all_ the ZPU boards I tested) that the credit number is some random hex number. I find that pretty weird, shouldn't that be cleared at start-up ?
 
Berzerk battery replacement

Assuming the RAM has no power and then the machine is started-up, with or without a battery, there could be a random number. It just depends on whether the programmers had enough programming space to add an initialization routine... or how much time they had to program... or upon how lazy they were. When we used to write programs on similar systems... back-in-the-day... we frequently didn't have enough ROM/RAM space for all the housekeeping we SHOULD have done. Sometimes we had a deadline and had to leave out "unnecessary" tasks. Sometimes we just got lazy and figured the end-user would only see it once or possibly not at all because it got tested before it shipped.

As for the battery...
If you put in a 3 Volt battery and a diode... you should not read more than 2.4-ish Volts at the IC, With a possible additional drop through R29, this may not be enough to sustain the memory. (I know it says 2.0Volts but it is probably very old too)

You say you actually measured 3.0 Volts at the IC, with power off?
As a test, you might try attaching the battery and diode directly to the chip and power cycle it. (bypassing R29)
If that still fails try adding another battery in series (3.0V + 1.5V) and the diode to see if the higher voltage gets you anywhere.

Kenneth
 
Assuming the RAM has no power and then the machine is started-up, with or without a battery, there could be a random number. It just depends on whether the programmers had enough programming space to add an initialization routine... or how much time they had to program... or upon how lazy they were. When we used to write programs on similar systems... back-in-the-day... we frequently didn't have enough ROM/RAM space for all the housekeeping we SHOULD have done. Sometimes we had a deadline and had to leave out "unnecessary" tasks. Sometimes we just got lazy and figured the end-user would only see it once or possibly not at all because it got tested before it shipped.

Well it could be. That would mean the hardware entirely relies on the battery to keep the correct values. I find it weird that a credit number would actually be stored at all in battery powered RAM.

As for the battery...
If you put in a 3 Volt battery and a diode... you should not read more than 2.4-ish Volts at the IC, With a possible additional drop through R29, this may not be enough to sustain the memory. (I know it says 2.0Volts but it is probably very old too)
In theory yes. However, batteries generally have a little higher voltage than specced. The "naked" battery measures 3.35V This is normal. Indeed the resistor and diode-drop lowers this voltage a bit, and the result is 3.08V at the RAM.
My first thought was about bypassing/removing the resistor too. Not sure if it's needed at all in this set-up (guess it's there for the charging, but I'm not sure).

You say you actually measured 3.0 Volts at the IC, with power off?
Yup, checked it again now (after 14 hrs.).It really should be enough. I think this is not the original 6514, it looks like it's been replaced on this board.

Gonna try bypassing R29 and also another type of battery that is rated at 3.6V (Like the original battery). Will also try a another 6514.

Thanks for thinking with me Kenneth !
 
Well it could be. That would mean the hardware entirely relies on the battery to keep the correct values. I find it weird that a credit number would actually be stored at all in battery powered RAM.

I don't know about the game in question, but I know that some games do indeed save credits in battery-backed RAM.
 
Back on topic.

I just installed a 3V lithium cell and a holder on the ZPU PCB.

To prevent the charge voltage from reaching the battery I added a blocking diode.

Hope you used a schottky to get a lower voltage drop.

I also noticed (but this is on _all_ the ZPU boards I tested) that the credit number is some random hex number. I find that pretty weird, shouldn't that be cleared at start-up ?

Nope... that's stored in the BRAM... what's even dumber is that only one nybble is battery backed, so the backed-up section of the RAM is all stored nybble-wise (like on williams games)
 
Hope you used a schottky to get a lower voltage drop.
No I didn't but the remaining voltage would be still enough right ?

Nope... that's stored in the BRAM... what's even dumber is that only one nybble is battery backed, so the backed-up section of the RAM is all stored nybble-wise (like on williams games)
Now there's a 80's word: nybble :D

Turned out I did the mod on one of the flaky boards I got, it's now giving 2 beeps and did so before but I forgot and it did run one or two times yesterday...weirdo, but could be a problem.
Will try it on a 100% running board.

So Mark, in theory this should work right ? I also think I can remove R29 right, this looks like it's a current limiter for the charginf voltage ?

O and I sent you a PM about the NVRAM boards...

Thanks
 
Was thinking: Since Berzerk shows only the top 5 scores after boot up (with random data in my case, being a fffffff score which is probably impossible to beat for even the world champion) does this mean it only saves the top 5 (Like Atari games that store the top 3 only) ?

And even more important, how do I clear those top-scores AND credits/ BRAM and what chip is exactly the BRAM ?
 
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Aaahhhh, the sweet taste of success after some struggle !

First I have to kick myself in the but (pretty hard to do). I found how to clear the memory in the service manual, page 14. I should have known ! RTFM ! :D

So cleared it, played a game, saved the score, power-cycle and YES the score is saved !!!

I decided instead of hooking up the diode to resistor R29 I would simply _replace_ R29 with the diode. Using a schottky as Mark suggest may actually be a good idea, I do get about of a half volt of power drop and measure 2.8V at the RAM now, but that should still be enough.

Anyway, this set-up works. I much prefered to go with the lithium solution because replacing it again with a chargeable battery would give worries about charging current, number of cycles it can go through (the battery I wanted to use can only do 1000 cycles as per Varta's spec. It's simply meant as a "stand-by" battery (like in fire alarms that are normally powered up 100% of the time).

Also, the lithium will stay good for years and is very easy to replace without soldering.

I will make some pics of the next board I mod to show how I did it.
 
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