CMOS RAM Error ~ Robotron

MonsterBash

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Kinda of an interesting problem. I fired up my games yesterday and got a CMOS RAM Error and then a 'open door to restore defaults' or something like that. This error was follwed be the initial all system operational message

So the first thing I do is check the voltages..I have 5.05 (using a switcher) at the ICs on both the ROM board and the CPU.

No big deal...I grab the backup CPU and ROM set and install for a quick fix as I have people coming over. Surprisingly I have the exact same error and problem.

Of course I opened the door and attempted to restore the defaults.

I've read here that the coin door switch actually completes the path to allow the temporary data to write to the CMOS. I thought this HAD to be the problem. I confirmed the switch is good in the game. I tried a new one with no change and removed and tried the working switch from my Sinistar. I've confirmed the wiring for the switch is intact at both ends with a continuity test from the MM

I've done numerous unplugs..reboots...with both boardset. Some with the batteries (new and tested) removed...some with the batteries installed

Some other notes:
In the menu all the text is garbage. On one boardset it's random garbage...the other boardset has consistent characters..but still garbage. Same with the high scores. One time I fired the boardset up and went into the menu and got through the test..I was asked to enter a high score name.

After a few back and forth board swaps and obviously rebooting, now the 'CMOS RAM Error' on both boards sets (amazingly exactly the same on both sets) is garage text as well. After a few few attempts one boardset boots normally (0 on ROM board) but I get no video output.

It's obviously not an boardset issue..but an environment issue. What the hell am I missing?
 
Seems like you've ruled out all but the power supply.

Have you tried another power supply ?

Also, a lot of games with switchers I've installed a 4700uf 25v capacitor
across the 5 volt and ground terminals. I had a Roadblasters always corrupting
its NVRAM. After I installed the cap I have yet to see the problem resurface.

JD
 
No I didn't. I'll give it a shot tomorrow

Seems like you've ruled out all but the power supply.

Have you tried another power supply ?

Also, a lot of games with switchers I've installed a 4700uf 25v capacitor
across the 5 volt and ground terminals. I had a Roadblasters always corrupting
its NVRAM. After I installed the cap I have yet to see the problem resurface.

JD
 
Had a similar issue with Defender and it ended up being one of the 5V pins on the power supply connector PCB. The pin had separated from the solder and was making an intermittent connection.
 
Had a similar issue with Defender and it ended up being one of the 5V pins on the power supply connector PCB. The pin had separated from the solder and was making an intermittent connection.

I just serviced a Robotron tonight with reset and Cmos issues.

All the supply pins were cracked and had to be resoldered.

JD
 
Don't know how many times we have to cover this, but your problem is that you are using a switching power supply to begin with.
Dok
 
So a machine I've owned since 1998 with a switcher in it..almost 15 years later has a 'compatibly issue' with a switcher?

I guess it's possible

Don't know how many times we have to cover this, but your problem is that you are using a switching power supply to begin with.
Dok
 
here are yellowdog's words from a past discussion: If the bit rot caused by the CPU hosing the CMOS is not bad enough, it won't cause the reset on the next power up, but all it takes is a few altered bytes in the CMOS to cause issues with the high score table. You can get the same effect with a linear power supply if you flip the switch on then off then on real quick. In that case, the big cap didn't have a chance to charge up and so the +5V dropped as fast as the +12V unregulated. The write protect circuit won't kick in quickly enough to protect the CMOS.
 
I should probably rebuild the linear PS but it been rock solid for over a decade without it.

I'll pull the PS from my Sinistar tonight and give it a shot
 
So a machine I've owned since 1998 with a switcher in it..almost 15 years later has a 'compatibly issue' with a switcher?
I guess it's possible

Some people believe the game timing is different using a switcher
and it's not the same game play.

I've always believed that was a crock. Steve Wagner maxed out the
high score on Joust in Yestercades and that's got a switcher as well as
the Defender, Joust and incoming Sinistar. We need the games to run
reliably 14-18 hours a day and I've replaced the analog power supplies
in about 40 of the machines there and nobody's complained yet.

JD
 
I can't perceive how the power source could alter the processor timing in anyway (what will affect the gameplay speed is failing ram chips/faulty rom ribbon cable/and anything that affects the "special chips" on the rom board. I suppose in theory you could alter the oscillator circuit on the mpu but that would be really trying hard.

LON rolled Joust on my mame cab last summer with no sweat which is running an old brutally hard emulation of Joust/Robotron so even at the far end of the spectrum Joust is managable to a trained player. :)
 
I've gotten that CMOS error and I am pretty sure it was caused by connector issues in my case. This was in a machine with a rebuilt power supply and no other known issues. Once the connection was fixed (ribbon cable), the error went away and did not come back. Coincidence? Probably not.

I have Williams games with switchers and some without. Some work fine, some work better with the original PS. My Robotron seems to be happier with the original one.
 
With switchers, you have to check ALL of the voltages at the RAM chips. I have seen switchers drift horribly from the specs over time. I just threw one out that had been working fine, then one day +5V = +5V, +12V = +9.75V, -5V = -11.23V. Fortunately, the boards were fine.

Always test the voltages at the RAM chips on Williams classic games. And do it monthly if you are using a switcher.

ken
 
all i know is cmos chips are notoriously sensitive to voltage changes...including static....i had one pop with .3v increase above 5...check the 5v
 
With switchers, you have to check ALL of the voltages at the RAM chips. I have seen switchers drift horribly from the specs over time. I just threw one out that had been working fine, then one day +5V = +5V, +12V = +9.75V, -5V = -11.23V. Fortunately, the boards were fine.

Always test the voltages at the RAM chips on Williams classic games. And do it monthly if you are using a switcher.

ken

just some follow-up to the recommendation for using a rebuilt linear supply.
I had an arcadeshop switcher that drifted with the temp of the garage every few days. I tried everything else including a new rom ribbon cable before figuring out the switcher was drifting.

put in a rebuilt supply then the machine went off to an arcade. it has been on 6 days a week since last summer, played hours a day. they haven't had to adjust the voltage pot once. and it only had one reset in all these months! unfriggin believable.
--the reset happened on a wave 39 style grunt wave on difficulty 10 around 6 million points. I attribute that to just a plain old glitch. has patched blue roms so it wasn't the shot in corner
 
Some people believe the game timing is different using a switcher
and it's not the same game play.

I've always believed that was a crock. Steve Wagner maxed out the
high score on Joust in Yestercades and that's got a switcher as well as
the Defender, Joust and incoming Sinistar. We need the games to run
reliably 14-18 hours a day and I've replaced the analog power supplies
in about 40 of the machines there and nobody's complained yet.

JD

Game timing doesn't have jack shit to do with the problem at hand. A switching power supply has absolutely nothing to do with game timing.

The switching power supply will not allow the game to store your settings before powering off. The big ass 18K cap on the linear power supply, hold power for 30-45 seconds to allow the CMOS to be written to and saved.
 
Game timing doesn't have jack shit to do with the problem at hand. A switching power supply has absolutely nothing to do with game timing.

The switching power supply will not allow the game to store your settings before powering off. The big ass 18K cap on the linear power supply, hold power for 30-45 seconds to allow the CMOS to be written to and saved.

Where did you come up with that theory ? That big ass 18K cap is a ripple
filter and nothing more.

JD
 
So I installed the linear PS from my Sinistar last night and I have the same problem. Both boardsets pop the CMOS RAM error on boot.

I repinned every connector at the PCB and ROM board and still nothing

I'm going to rebuild the linear PS and check all the voltages at the RAM chips...it's something I've been wanting to do anyway

I'd guess if the switcher drifted high and did take out the CMOS stuff...the second boardset might have been damaged also

On a side note when I tested the voltages initially...the 5V was at 4.89.

On more thing..when I'm running through the tests from the menu..when I get to the CMOS test the screen goes blank. I get a 3 1...then another 3 1 from the ROM board. The CMOS error is back on the screen then the ROM board flips to 0. Note sure if this in normal or not as I never noticed it before
 
On a side note when I tested the voltages initially...the 5V was at 4.89.

Measured at the pins of the RAM chips themselves? I recall there can be up to .5v drop between the power source and those pins. Which is why yellowdog pointed out the importance of testing voltages directly at the chip pins themselves
 
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