Hi all, I was asked by a fellow collector to look into the idea of replacing the battery backed RAM on a Gottlieb Q*Bert board with some Dallas battery backed SRAM. It also led to finding another problem with affected at least 3 Q*Bert boards. The high-scores would become corrupted or just reset everytime the machine powered on, this was regardless of whether the original battery backed ram was used or not. More on that at the end.. ------------------------------------------------------------------ I've put a couple of pictures up: Picture 1 http://www.jrok.com/sohs/qb1.jpg Picture 2 http://www.jrok.com/sohs/qb2.jpg Changing the RAM ================= To accomplish this you need to make only two board modifications, and add some RAM. 1. Remove the battery ! 2. 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. See picture 1. Note: Diode d2 is right next to the battery just above the socket for ROM4. Note: In picture 1 the jumper wire is soldered to a different starting point but it achieves the same goal. 3. Replace RAM0 and RAM1 with Dallas DS1225 battery backed SRAM, now... depending on what your powersupply is like you may need to use the DS1225AD ( 4.5 write protect voltage ) or DS1225AD ( 4.75 write protect ). See picture 2. 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 DS1225AD part. Now that should be it, your Q*Bert will be using battery backed RAM with at least a ten year lifespan, in a package that, unlike the original battery, won't leak acid all over your board. 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 goofey state and corrupting everything. Simple 20 second fix. 1. 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 doesnt hurt ). This would appear to have fixed the problem in all three boards. ------------------------------------------------------------------ Thanks go to Steve Zuener for testing my fixes :-) Cheers James ----------------------------------- email replies change nowhere to com JrokLand http://www.jrok.com ----------------------------------- >3. Replace RAM0 and RAM1 with Dallas DS1225 battery backed SRAM, > now... depending on what your powersupply is like you may > need to use the DS1225AD ( 4.5 write protect voltage ) > or DS1225AD ( 4.75 write protect ). See picture 2. Dooohhh... I specified completely the wrong part number there, It should be the Dallas DS1220AD, that's the 2k x 8 RAM. The DS1225 is an 8k x 8 device. OoOpps.. The picture of the board with the RAM plugged in is correct. Cheers James I tried this mod and it works great. I used the Dallas DS1220AD RAM. Although the 1200AB may work for some boards, it's power on voltage is a tad higher than the AD and as a result shut down frequently on my board. power on voltage: DS1220AB is 4.5VDC, DS1220AD is 4.25VDC Thanks for sharing this mod! No leaking worrys now ;) James Hagen