Q*BERT Battery Backed RAM upgrade 
All great fans of Q*Bert know the game saves it's high
score table, this is performed by two low power Static RAMs and a DataSentry battery
backup. Owners of game will also know all about the nasty habit, seeing as they're now
about 16 years old, of the aged battery either dying and/or LEAKING acid over the board !
So.. in an attempted to remedy this from ever happening, I
removed the battery and simply modified a board to work with the Dallas SRAM I'm so fond
of.
Overall very little needs to be done the battery must be removed, a jumper wire
installed and two Dallas SRAM plugged into the board. This will give you 10 years of saved
high-scores... should be enough to keep most folks happy. If anyone's really interested I
could look at doing the modification using a Xicor X20C17: high speed
AUTOSTORE™ NOVRAM, this unit allows 1,000,000 back up writes when the power is
turned off, so if you turned the machine on and off every hour... it's still work for 114
years... .
As part of this project I also discovered another problem
which was occurring to three other Q*Bert boards. Even though the high-scores were being
saved, they would get reset or corrupted without warning ! This turned out to be a reset
error, the capacitor which gives a delay on the CPU reset was failing, causing the CPU
reset to be too short a time period. This was fixed by replacement of capacitor C25 with a
470uF electrolytic.
Game Enhancements
1. Battery backed RAM enhancement
2. Reset fix
Known issues
1. None
Upgrading
Changing the RAM
To accomplish this you need to make only two board
modifications, and to add some RAM.
Remove the battery !
Remove diode D2 and replace it with a wire, or just solder
a wire over D2. This takes the power line for the two battery backed RAMs to directly 5v.
Note: Diode d2 is right next to the battery just above the socket for
ROM4.
Note: In the picture on my site the jumper wire is soldered to a
different point but it achieves the same goal.
Replace RAM0 and RAM1 with Dallas DS1220 battery backed
SRAM, now... depending on what your power supply is like you may need to use the DS1220AD
( 4.5 write protect voltage ) or DS1220AB ( 4.75 write protect ). See picture 2.
Note:At least one Q*Bert I've come across has a really nasty PSU that
just about gives out nearly 5.0v, so the voltage at the RAM comes in at UNDER 4.75, thus
putting the AB part into it's write protect state.
To be on the safe side I'd opt for the DS1220AD part.
That should be it, your Q*Bert will be using battery
backed RAM with at least a ten year lifespan, in a package which, unlike the original
battery, won't leak acid all over your board.
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Battery Removed and Jumper wire soldered in place
Picture 1
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Larger View of board with RAM in place and 470uF
replacement capacitor
Picture 2
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Corrupted Scores Fix
This was a condition that effected at least 3 boards
and was driving at least one person mad.
What would happen is that everytime the game was powered down, the scores would become
corrupted or lost. Now, I was sure there was nothing wrong with the battery back up ( in
fact it would do this on an original Q*Bert board WITHOUT the dallas hack ) so it had to
be processor related.
Turned out to be the reset line ! The reset line on the 8088 was not being held active for
long enough, so the CPU was starting in some kind of goofy state and corrupting
everything.
Simple 20 second fix.
Replace capacitor c25 ! originally c25 was a 100uF,
but I changed it for a 470uF cap ( mostly because that was what I had to hand at the time
and a longer reset pulse doesn't hurt ).
Restart the machine
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